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Network Working Group                                      B. FraserRequest for Comments: 2196                                    EditorFYI: 8                                                       SEI/CMUObsoletes:1244                                       September 1997Category: InformationalSite Security HandbookStatus of this Memo   This memo provides information for the Internet community.  It does   not specify an Internet standard of any kind.  Distribution of this   memo is unlimited.Abstract   This handbook is a guide to developing computer security policies and   procedures for sites that have systems on the Internet.  The purpose   of this handbook is to provide practical guidance to administrators   trying to secure their information and services.  The subjects   covered include policy content and formation, a broad range of   technical system and network security topics, and security incident   response.Table of Contents1.   Introduction....................................................21.1  Purpose of this Work............................................31.2  Audience........................................................31.3  Definitions.....................................................31.4  Related Work....................................................41.5  Basic Approach..................................................41.6  Risk Assessment.................................................52.   Security Policies...............................................62.1  What is a Security Policy and Why Have One?.....................62.2  What Makes a Good Security Policy?..............................92.3  Keeping the Policy Flexible.....................................113.   Architecture....................................................113.1  Objectives......................................................113.2  Network and Service Configuration...............................143.3  Firewalls.......................................................204.   Security Services and Procedures................................244.1  Authentication..................................................244.2  Confidentiality.................................................284.3  Integrity.......................................................28Fraser, Ed.                Informational                        [Page 1]

RFC 2196              Site Security Handbook              September 19974.4  Authorization...................................................294.5  Access..........................................................304.6  Auditing........................................................344.7  Securing Backups................................................375.   Security Incident Handling......................................375.1  Preparing and Planning for Incident Handling....................395.2  Notification and Points of Contact..............................425.3  Identifying an Incident.........................................505.4  Handling an Incident............................................525.5  Aftermath of an Incident........................................585.6  Responsibilities................................................596.   Ongoing Activities..............................................607.   Tools and Locations.............................................608.   Mailing Lists and Other Resources...............................629.   References......................................................641.  Introduction   This document provides guidance to system and network administrators   on how to address security issues within the Internet community.  It   builds on the foundation provided inRFC 1244 and is the collective   work of a number of contributing authors. Those authors include:   Jules P. Aronson (aronson@nlm.nih.gov), Nevil Brownlee   (n.brownlee@auckland.ac.nz), Frank Byrum (byrum@norfolk.infi.net),   Joao Nuno Ferreira (ferreira@rccn.net), Barbara Fraser   (byf@cert.org), Steve Glass (glass@ftp.com), Erik Guttman   (erik.guttman@eng.sun.com), Tom Killalea (tomk@nwnet.net), Klaus-   Peter Kossakowski (kossakowski@cert.dfn.de), Lorna Leone   (lorna@staff.singnet.com.sg), Edward.P.Lewis   (Edward.P.Lewis.1@gsfc.nasa.gov), Gary Malkin (gmalkin@xylogics.com),   Russ Mundy (mundy@tis.com), Philip J. Nesser   (pjnesser@martigny.ai.mit.edu), and Michael S. Ramsey   (msr@interpath.net).   In addition to the principle writers, a number of reviewers provided   valuable comments. Those reviewers include: Eric Luiijf   (luiijf@fel.tno.nl), Marijke Kaat (marijke.kaat@sec.nl), Ray Plzak   (plzak@nic.mil) and Han Pronk (h.m.pronk@vka.nl).   A special thank you goes to Joyce Reynolds, ISI, and Paul Holbrook,   CICnet, for their vision, leadership, and effort in the creation of   the first version of this handbook. It is the working group's sincere   hope that this version will be as helpful to the community as the   earlier one was.Fraser, Ed.                Informational                        [Page 2]

RFC 2196              Site Security Handbook              September 19971.1  Purpose of This Work   This handbook is a guide to setting computer security policies and   procedures for sites that have systems on the Internet (however, the   information provided should also be useful to sites not yet connected   to the Internet).  This guide lists issues and factors that a site   must consider when setting their own policies.  It makes a number of   recommendations and provides discussions of relevant areas.   This guide is only a framework for setting security policies and   procedures.  In order to have an effective set of policies and   procedures, a site will have to make many decisions, gain agreement,   and then communicate and implement these policies.1.2  Audience   The audience for this document are system and network administrators,   and decision makers (typically "middle management") at sites.  For   brevity, we will use the term "administrator" throughout this   document to refer to system and network administrators.   This document is not directed at programmers or those trying to   create secure programs or systems.  The focus of this document is on   the policies and procedures that need to be in place to support the   technical security features that a site may be implementing.   The primary audience for this work are sites that are members of the   Internet community.  However, this document should be useful to any   site that allows communication with other sites.  As a general guide   to security policies, this document may also be useful to sites with   isolated systems.1.3  Definitions   For the purposes of this guide, a "site" is any organization that   owns computers or network-related resources. These resources may   include host computers that users use, routers, terminal servers, PCs   or other devices that have access to the Internet.  A site may be an   end user of Internet services or a service provider such as a mid-   level network.  However, most of the focus of this guide is on those   end users of Internet services.  We assume that the site has the   ability to set policies and procedures for itself with the   concurrence and support from those who actually own the resources. It   will be assumed that sites that are parts of larger organizations   will know when they need to consult, collaborate, or take   recommendations from, the larger entity.Fraser, Ed.                Informational                        [Page 3]

RFC 2196              Site Security Handbook              September 1997   The "Internet" is a collection of thousands of networks linked by a   common set of technical protocols which make it possible for users of   any one of the networks to communicate with, or use the services   located on, any of the other networks (FYI4,RFC 1594).   The term "administrator" is used to cover all those people who are   responsible for the day-to-day operation of system and network   resources.  This may be a number of individuals or an organization.   The term "security administrator" is used to cover all those people   who are responsible for the security of information and information   technology.  At some sites this function may be combined with   administrator (above); at others, this will be a separate position.   The term "decision maker" refers to those people at a site who set or   approve policy.  These are often (but not always) the people who own   the resources.1.4  Related Work   The Site Security Handbook Working Group is working on a User's Guide   to Internet Security. It will provide practical guidance to end users   to help them protect their information and the resources they use.1.5  Basic Approach   This guide is written to provide basic guidance in developing a   security plan for your site.  One generally accepted approach to   follow is suggested by Fites, et. al. [Fites 1989] and includes the   following steps:   (1)  Identify what you are trying to protect.   (2)  Determine what you are trying to protect it from.   (3)  Determine how likely the threats are.   (4)  Implement measures which will protect your assets in a cost-        effective manner.   (5)  Review the process continuously and make improvements each time        a weakness is found.   Most of this document is focused on item 4 above, but the other steps   cannot be avoided if an effective plan is to be established at your   site.  One old truism in security is that the cost of protecting   yourself against a threat should be less than the cost of recovering   if the threat were to strike you.  Cost in this context should be   remembered to include losses expressed in real currency, reputation,   trustworthiness, and other less obvious measures.  Without reasonable   knowledge of what you are protecting and what the likely threats are,   following this rule could be difficult.Fraser, Ed.                Informational                        [Page 4]

RFC 2196              Site Security Handbook              September 19971.6  Risk Assessment1.6.1  General Discussion   One of the most important reasons for creating a computer security   policy is to ensure that efforts spent on security yield cost   effective benefits.  Although this may seem obvious, it is possible   to be mislead about where the effort is needed.  As an example, there   is a great deal of publicity about intruders on computers systems;   yet most surveys of computer security show that, for most   organizations, the actual loss from "insiders" is much greater.   Risk analysis involves determining what you need to protect, what you   need to protect it from, and how to protect it.  It is the process of   examining all of your risks, then ranking those risks by level of   severity.  This process involves making cost-effective decisions on   what you want to protect.  As mentioned above, you should probably   not spend more to protect something than it is actually worth.   A full treatment of risk analysis is outside the scope of this   document.  [Fites 1989] and [Pfleeger 1989] provide introductions to   this topic.  However, there are two elements of a risk analysis that   will be briefly covered in the next two sections:   (1) Identifying the assets   (2) Identifying the threats   For each asset, the basic goals of security are availability,   confidentiality, and integrity.  Each threat should be examined with   an eye to how the threat could affect these areas.1.6.2  Identifying the Assets   One step in a risk analysis is to identify all the things that need   to be protected.  Some things are obvious, like valuable proprietary   information, intellectual property, and all the various pieces of   hardware; but, some are overlooked, such as the people who actually   use the systems. The essential point is to list all things that could   be affected by a security problem.   One list of categories is suggested by Pfleeger [Pfleeger 1989]; this   list is adapted from that source:   (1)  Hardware: CPUs, boards, keyboards, terminals,        workstations, personal computers, printers, disk        drives, communication lines, terminal servers, routers.Fraser, Ed.                Informational                        [Page 5]

RFC 2196              Site Security Handbook              September 1997   (2)  Software: source programs, object programs,        utilities, diagnostic programs, operating systems,        communication programs.   (3)  Data: during execution, stored on-line, archived off-line,        backups, audit logs, databases, in transit over        communication media.   (4)  People: users, administrators, hardware maintainers.   (5)  Documentation: on programs, hardware, systems, local        administrative procedures.   (6)  Supplies: paper, forms, ribbons, magnetic media.1.6.3  Identifying the Threats   Once the assets requiring protection are identified, it is necessary   to identify threats to those assets.  The threats can then be   examined to determine what potential for loss exists.  It helps to   consider from what threats you are trying to protect your assets.   The following are classic threats that should be considered.   Depending on your site, there will be more specific threats that   should be identified and addressed.   (1)  Unauthorized access to resources and/or information   (2)  Unintented and/or unauthorized Disclosure of information   (3)  Denial of service2.  Security Policies   Throughout this document there will be many references to policies.   Often these references will include recommendations for specific   policies. Rather than repeat guidance in how to create and   communicate such a policy, the reader should apply the advice   presented in this chapter when developing any policy recommended   later in this book.2.1  What is a Security Policy and Why Have One?   The security-related decisions you make, or fail to make, as   administrator largely determines how secure or insecure your network   is, how much functionality your network offers, and how easy your   network is to use.  However, you cannot make good decisions about   security without first determining what your security goals are.   Until you determine what your security goals are, you cannot make   effective use of any collection of security tools because you simply   will not know what to check for and what restrictions to impose.Fraser, Ed.                Informational                        [Page 6]

RFC 2196              Site Security Handbook              September 1997   For example, your goals will probably be very different from the   goals of a product vendor.  Vendors are trying to make configuration   and operation of their products as simple as possible, which implies   that the default configurations will often be as open (i.e.,   insecure) as possible.  While this does make it easier to install new   products, it also leaves access to those systems, and other systems   through them, open to any user who wanders by.   Your goals will be largely determined by the following key tradeoffs:   (1)  services offered versus security provided -        Each service offered to users carries its own security risks.        For some services the risk outweighs the benefit of the service        and the administrator may choose to eliminate the service rather        than try to secure it.   (2)  ease of use versus security -        The easiest system to use would allow access to any user and        require no passwords; that is, there would be no security.        Requiring passwords makes the system a little less convenient,        but more secure.  Requiring device-generated one-time passwords        makes the system even more difficult to use, but much more        secure.   (3)  cost of security versus risk of loss -        There are many different costs to security: monetary (i.e., the        cost of purchasing security hardware and software like firewalls        and one-time password generators), performance (i.e., encryption        and decryption take time), and ease of use (as mentioned above).        There are also many levels of risk: loss of privacy (i.e., the        reading of information by unauthorized individuals), loss of        data (i.e., the corruption or erasure of information), and the        loss of service (e.g., the filling of data storage space, usage        of computational resources, and denial of network access).  Each        type of cost must be weighed against each type of loss.   Your goals should be communicated to all users, operations staff, and   managers through a set of security rules, called a "security policy."   We are using this term, rather than the narrower "computer security   policy" since the scope includes all types of information technology   and the information stored and manipulated by the technology.2.1.1  Definition of a Security Policy   A security policy is a formal statement of the rules by which people   who are given access to an organization's technology and information   assets must abide.Fraser, Ed.                Informational                        [Page 7]

RFC 2196              Site Security Handbook              September 19972.1.2  Purposes of a Security Policy   The main purpose of a security policy is to inform users, staff and   managers of their obligatory requirements for protecting technology   and information assets.  The policy should specify the mechanisms   through which these requirements can be met.  Another purpose is to   provide a baseline from which to acquire, configure and audit   computer systems and networks for compliance with the policy.   Therefore an attempt to use a set of security tools in the absence of   at least an implied security policy is meaningless.   An Appropriate Use Policy (AUP) may also be part of a security   policy.  It should spell out what users shall and shall not do on the   various components of the system, including the type of traffic   allowed on the networks.  The AUP should be as explicit as possible   to avoid ambiguity or misunderstanding.  For example, an AUP might   list any prohibited USENET newsgroups. (Note: Appropriate Use Policy   is referred to as Acceptable Use Policy by some sites.)2.1.3  Who Should be Involved When Forming Policy?   In order for a security policy to be appropriate and effective, it   needs to have the acceptance and support of all levels of employees   within the organization.  It is especially important that corporate   management fully support the security policy process otherwise there   is little chance that they will have the intended impact.  The   following is a list of individuals who should be involved in the   creation and review of security policy documents:   (1)  site security administrator   (2)  information technology technical staff (e.g., staff from        computing center)   (3)  administrators of large user groups within the organization        (e.g., business divisions, computer science department within a        university, etc.)   (4)  security incident response team   (5)  representatives of the user groups affected by the security        policy   (6)  responsible management   (7)  legal counsel (if appropriate)   The list above is representative of many organizations, but is not   necessarily comprehensive.  The idea is to bring in representation   from key stakeholders, management who have budget and policy   authority, technical staff who know what can and cannot be supported,   and legal counsel who know the legal ramifications of various policyFraser, Ed.                Informational                        [Page 8]

RFC 2196              Site Security Handbook              September 1997   choices.  In some organizations, it may be appropriate to include EDP   audit personnel.  Involving this group is important if resulting   policy statements are to reach the broadest possible acceptance.  It   is also relevant to mention that the role of legal counsel will also   vary from country to country.2.2  What Makes a Good Security Policy?   The characteristics of a good security policy are:   (1)  It must be implementable through system administration        procedures, publishing of acceptable use guidelines, or other        appropriate methods.   (2)  It must be enforcible with security tools, where appropriate,        and with sanctions, where actual prevention is not technically        feasible.   (3)  It must clearly define the areas of responsibility for the        users, administrators, and management.   The components of a good security policy include:   (1)  Computer Technology Purchasing Guidelines which specify        required, or preferred, security features.  These should        supplement existing purchasing policies and guidelines.   (2)  A Privacy Policy which defines reasonable expectations of        privacy regarding such issues as monitoring of electronic mail,        logging of keystrokes, and access to users' files.   (3)  An Access Policy which defines access rights and privileges to        protect assets from loss or disclosure by specifying acceptable        use guidelines for users, operations staff, and management.  It        should provide guidelines for external connections, data        communications, connecting devices to a network, and adding new        software to systems.  It should also specify any required        notification messages (e.g., connect messages should provide        warnings about authorized usage and line monitoring, and not        simply say "Welcome").   (4)  An Accountability Policy which defines the responsibilities of        users, operations staff, and management.  It should specify an        audit capability, and provide incident handling guidelines        (i.e., what to do and who to contact if a possible intrusion is        detected).Fraser, Ed.                Informational                        [Page 9]

RFC 2196              Site Security Handbook              September 1997   (5)  An Authentication Policy which establishes trust through an        effective password policy, and by setting guidelines for remote        location authentication and the use of authentication devices        (e.g., one-time passwords and the devices that generate them).   (6)  An Availability statement which sets users' expectations for the        availability of resources.  It should address redundancy and        recovery issues, as well as specify operating hours and        maintenance down-time periods.  It should also include contact        information for reporting system and network failures.   (7)  An Information Technology System & Network Maintenance Policy        which describes how both internal and external maintenance        people are allowed to handle and access technology. One        important topic to be addressed here is whether remote        maintenance is allowed and how such access is controlled.        Another area for consideration here is outsourcing and how it is        managed.   (8)  A Violations Reporting Policy that indicates which types of        violations (e.g., privacy and security, internal and external)        must be reported and to whom the reports are made.  A non-        threatening atmosphere and the possibility of anonymous        reporting will result in a greater probability that a violation        will be reported if it is detected.   (9)  Supporting Information which provides users, staff, and        management with contact information for each type of policy        violation; guidelines on how to handle outside queries about a        security incident, or information which may be considered        confidential or proprietary; and cross-references to security        procedures and related information, such as company policies and        governmental laws and regulations.   There may be regulatory requirements that affect some aspects of your   security policy (e.g., line monitoring).  The creators of the   security policy should consider seeking legal assistance in the   creation of the policy.  At a minimum, the policy should be reviewed   by legal counsel.   Once your security policy has been established it should be clearly   communicated to users, staff, and management.  Having all personnel   sign a statement indicating that they have read, understood, and   agreed to abide by the policy is an important part of the process.   Finally, your policy should be reviewed on a regular basis to see if   it is successfully supporting your security needs.Fraser, Ed.                Informational                       [Page 10]

RFC 2196              Site Security Handbook              September 19972.3  Keeping the Policy Flexible   In order for a security policy to be viable for the long term, it   requires a lot of flexibility based upon an architectural security   concept. A security policy should be (largely) independent from   specific hardware and software situations (as specific systems tend   to be replaced or moved overnight).  The mechanisms for updating the   policy should be clearly spelled out.  This includes the process, the   people involved, and the people who must sign-off on the changes.   It is also important to recognize that there are exceptions to every   rule.  Whenever possible, the policy should spell out what exceptions   to the general policy exist.  For example, under what conditions is a   system administrator allowed to go through a user's files.  Also,   there may be some cases when multiple users will have access to the   same userid.  For example, on systems with a "root" user, multiple   system administrators may know the password and use the root account.   Another consideration is called the "Garbage Truck Syndrome."  This   refers to what would happen to a site if a key person was suddenly   unavailable for his/her job function (e.g., was suddenly ill or left   the company unexpectedly).  While the greatest security resides in   the minimum dissemination of information, the risk of losing critical   information increases when that information is not shared.  It is   important to determine what the proper balance is for your site.3.  Architecture3.1  Objectives3.1.1  Completely Defined Security Plans   All sites should define a comprehensive security plan.  This plan   should be at a higher level than the specific policies discussed in   chapter 2, and it should be crafted as a framework of broad   guidelines into which specific policies will fit.   It is important to have this framework in place so that individual   policies can be consistent with the overall site security   architecture.  For example, having a strong policy with regard to   Internet access and having weak restrictions on modem usage is   inconsistent with an overall philosophy of strong security   restrictions on external access.   A security plan should define: the list of network services that will   be provided; which areas of the organization will provide the   services; who will have access to those services; how access will be   provided; who will administer those services; etc.Fraser, Ed.                Informational                       [Page 11]

RFC 2196              Site Security Handbook              September 1997   The plan should also address how incident will be handled.  Chapter 5   provides an in-depth discussion of this topic, but it is important   for each site to define classes of incidents and corresponding   responses.  For example, sites with firewalls should set a threshold   on the number of attempts made to foil the firewall before triggering   a response?  Escallation levels should be defined for both attacks   and responses.  Sites without firewalls will have to determine if a   single attempt to connect to a host constitutes an incident? What   about a systematic scan of systems?   For sites connected to the Internet, the rampant media magnification   of Internet related security incidents can overshadow a (potentially)   more serious internal security problem.  Likewise, companies who have   never been connected to the Internet may have strong, well defined,   internal policies but fail to adequately address an external   connection policy.3.1.2  Separation of Services   There are many services which a site may wish to provide for its   users, some of which may be external.  There are a variety of   security reasons to attempt to isolate services onto dedicated host   computers.  There are also performance reasons in most cases, but a   detailed discussion is beyond to scope of this document.   The services which a site may provide will, in most cases, have   different levels of access needs and models of trust.  Services which   are essential to the security or smooth operation of a site would be   better off being placed on a dedicated machine with very limited   access (seeSection 3.1.3 "deny all" model), rather than on a machine   that provides a service (or services) which has traditionally been   less secure, or requires greater accessability by users who may   accidentally suborn security.   It is also important to distinguish between hosts which operate   within different models of trust (e.g., all the hosts inside of a   firewall and any host on an exposed network).   Some of the services which should be examined for potential   separation are outlined insection 3.2.3. It is important to remember   that security is only as strong as the weakest link in the chain.   Several of the most publicized penetrations in recent years have been   through the exploitation of vulnerabilities in electronic mail   systems.  The intruders were not trying to steal electronic mail, but   they used the vulnerability in that service to gain access to other   systems.Fraser, Ed.                Informational                       [Page 12]

RFC 2196              Site Security Handbook              September 1997   If possible, each service should be running on a different machine   whose only duty is to provide a specific service.  This helps to   isolate intruders and limit potential harm.3.1.3  Deny all/ Allow all   There are two diametrically opposed underlying philosophies which can   be adopted when defining a security plan.  Both alternatives are   legitimate models to adopt, and the choice between them will depend   on the site and its needs for security.   The first option is to turn off all services and then selectively   enable services on a case by case basis as they are needed. This can   be done at the host or network level as appropriate.  This model,   which will here after be referred to as the "deny all" model, is   generally more secure than the other model described in the next   paragraph.  More work is required to successfully implement a "deny   all" configuration as well as a better understanding of services.   Allowing only known services provides for a better analysis of a   particular service/protocol and the design of a security mechanism   suited to the security level of the site.   The other model, which will here after be referred to as the "allow   all" model, is much easier to implement, but is generally less secure   than the "deny all" model.  Simply turn on all services, usually the   default at the host level, and allow all protocols to travel across   network boundaries, usually the default at the router level.  As   security holes become apparent, they are restricted or patched at   either the host or network level.   Each of these models can be applied to different portions of the   site, depending on functionality requirements, administrative   control, site policy, etc.  For example, the policy may be to use the   "allow all" model when setting up workstations for general use, but   adopt a "deny all" model when setting up information servers, like an   email hub.  Likewise, an "allow all" policy may be adopted for   traffic between LAN's internal to the site, but a "deny all" policy   can be adopted between the site and the Internet.   Be careful when mixing philosophies as in the examples above.  Many   sites adopt the theory of a hard "crunchy" shell and a soft "squishy"   middle.  They are willing to pay the cost of security for their   external traffic and require strong security measures, but are   unwilling or unable to provide similar protections internally.  This   works fine as long as the outer defenses are never breached and the   internal users can be trusted.  Once the outer shell (firewall) is   breached, subverting the internal network is trivial.Fraser, Ed.                Informational                       [Page 13]

RFC 2196              Site Security Handbook              September 19973.1.4  Identify Real Needs for Services   There is a large variety of services which may be provided, both   internally and on the Internet at large.  Managing security is, in   many ways, managing access to services internal to the site and   managing how internal users access information at remote sites.   Services tend to rush like waves over the Internet.  Over the years   many sites have established anonymous FTP servers, gopher servers,   wais servers, WWW servers, etc. as they became popular, but not   particularly needed, at all sites.  Evaluate all new services that   are established with a skeptical attitude to determine if they are   actually needed or just the current fad sweeping the Internet.   Bear in mind that security complexity can grow exponentially with the   number of services provided.  Filtering routers need to be modified   to support the new protocols.  Some protocols are inherently   difficult to filter safely (e.g., RPC and UDP services), thus   providing more openings to the internal network.  Services provided   on the same machine can interact in catastrophic ways.  For example,   allowing anonymous FTP on the same machine as the WWW server may   allow an intruder to place a file in the anonymous FTP area and cause   the HTTP server to execute it.3.2  Network and Service Configuration3.2.1  Protecting the Infrastructure   Many network administrators go to great lengths to protect the hosts   on their networks.  Few administrators make any effort to protect the   networks themselves.  There is some rationale to this.  For example,   it is far easier to protect a host than a network.  Also, intruders   are likely to be after data on the hosts; damaging the network would   not serve their purposes.  That said, there are still reasons to   protect the networks.  For example, an intruder might divert network   traffic through an outside host in order to examine the data (i.e.,   to search for passwords).  Also, infrastructure includes more than   the networks and the routers which interconnect them.  Infrastructure   also includes network management (e.g., SNMP), services (e.g., DNS,   NFS, NTP, WWW), and security (i.e., user authentication and access   restrictions).   The infrastructure also needs protection against human error.  When   an administrator misconfigures a host, that host may offer degraded   service.  This only affects users who require that host and, unlessFraser, Ed.                Informational                       [Page 14]

RFC 2196              Site Security Handbook              September 1997   that host is a primary server, the number of affected users will   therefore be limited.  However, if a router is misconfigured, all   users who require the network will be affected.  Obviously, this is a   far larger number of users than those depending on any one host.3.2.2  Protecting the Network   There are several problems to which networks are vulnerable.  The   classic problem is a "denial of service" attack.  In this case, the   network is brought to a state in which it can no longer carry   legitimate users' data.  There are two common ways this can be done:   by attacking the routers and by flooding the network with extraneous   traffic.  Please note that the term "router" in this section is used   as an example of a larger class of active network interconnection   components that also includes components like firewalls, proxy-   servers, etc.   An attack on the router is designed to cause it to stop forwarding   packets, or to forward them improperly.  The former case may be due   to a misconfiguration, the injection of a spurious routing update, or   a "flood attack" (i.e., the router is bombarded with unroutable   packets, causing its performance to degrade).  A flood attack on a   network is similar to a flood attack on a router, except that the   flood packets are usually broadcast.  An ideal flood attack would be   the injection of a single packet which exploits some known flaw in   the network nodes and causes them to retransmit the packet, or   generate error packets, each of which is picked up and repeated by   another host.  A well chosen attack packet can even generate an   exponential explosion of transmissions.   Another classic problem is "spoofing."  In this case, spurious   routing updates are sent to one or more routers causing them to   misroute packets.  This differs from a denial of service attack only   in the purpose behind the spurious route.  In denial of service, the   object is to make the router unusable; a state which will be quickly   detected by network users.  In spoofing, the spurious route will   cause packets to be routed to a host from which an intruder may   monitor the data in the packets.  These packets are then re-routed to   their correct destinations.  However, the intruder may or may not   have altered the contents of the packets.   The solution to most of these problems is to protect the routing   update packets sent by the routing protocols in use (e.g., RIP-2,   OSPF).  There are three levels of protection: clear-text password,   cryptographic checksum, and encryption.  Passwords offer only minimal   protection against intruders who do not have direct access to the   physical networks.  Passwords also offer some protection against   misconfigured routers (i.e, routers which, out of the box, attempt toFraser, Ed.                Informational                       [Page 15]

RFC 2196              Site Security Handbook              September 1997   route packets).  The advantage of passwords is that they have a very   low overhead, in both bandwidth and CPU consumption.  Checksums   protect against the injection of spurious packets, even if the   intruder has direct access to the physical network.  Combined with a   sequence number, or other unique identifier, a checksum can also   protect again "replay" attacks, wherein an old (but valid at the   time) routing update is retransmitted by either an intruder or a   misbehaving router.  The most security is provided by complete   encryption of sequenced, or uniquely identified, routing updates.   This prevents an intruder from determining the topology of the   network.  The disadvantage to encryption is the overhead involved in   processing the updates.   RIP-2 (RFC 1723) and OSPF (RFC 1583) both support clear-text   passwords in their base design specifications.  In addition, there   are extensions to each base protocol to support MD5 encryption.   Unfortunately, there is no adequate protection against a flooding   attack, or a misbehaving host or router which is flooding the   network.  Fortunately, this type of attack is obvious when it occurs   and can usually be terminated relatively simply.3.2.3  Protecting the Services   There are many types of services and each has its own security   requirements.  These requirements will vary based on the intended use   of the service.  For example, a service which should only be usable   within a site (e.g., NFS) may require different protection mechanisms   than a service provided for external use. It may be sufficient to   protect the internal server from external access.  However, a WWW   server, which provides a home page intended for viewing by users   anywhere on the Internet, requires built-in protection.  That is, the   service/protocol/server must provide whatever security may be   required to prevent unauthorized access and modification of the Web   database.   Internal services (i.e., services meant to be used only by users   within a site) and external services (i.e., services deliberately   made available to users outside a site) will, in general, have   protection requirements which differ as previously described.  It is   therefore wise to isolate the internal services to one set of server   host computers and the external services to another set of server   host computers.  That is, internal and external servers should not be   co-located on the same host computer.  In fact, many sites go so farFraser, Ed.                Informational                       [Page 16]

RFC 2196              Site Security Handbook              September 1997   as to have one set of subnets (or even different networks) which are   accessible from the outside and another set which may be accessed   only within the site.  Of course, there is usually a firewall which   connects these partitions.  Great care must be taken to ensure that   such a firewall is operating properly.   There is increasing interest in using intranets to connect different   parts of a organization (e.g., divisions of a company). While this   document generally differentiates between external and internal   (public and private), sites using intranets should be aware that they   will need to consider three separations and take appropriate actions   when designing and offering services. A service offered to an   intranet would be neither public, nor as completely private as a   service to a single organizational subunit. Therefore, the service   would need its own supporting system, separated from both external   and internal services and networks.   One form of external service deserves some special consideration, and   that is anonymous, or guest, access.  This may be either anonymous   FTP or guest (unauthenticated) login.  It is extremely important to   ensure that anonymous FTP servers and guest login userids are   carefully isolated from any hosts and file systems from which outside   users should be kept.  Another area to which special attention must   be paid concerns anonymous, writable access.  A site may be legally   responsible for the content of publicly available information, so   careful monitoring of the information deposited by anonymous users is   advised.   Now we shall consider some of the most popular services: name   service, password/key service, authentication/proxy service,   electronic mail, WWW, file transfer, and NFS.  Since these are the   most frequently used services, they are the most obvious points of   attack.  Also, a successful attack on one of these services can   produce disaster all out of proportion to the innocence of the basic   service.3.2.3.1  Name Servers (DNS and NIS(+))   The Internet uses the Domain Name System (DNS) to perform address   resolution for host and network names.  The Network Information   Service (NIS) and NIS+ are not used on the global Internet, but are   subject to the same risks as a DNS server.  Name-to-address   resolution is critical to the secure operation of any network.  An   attacker who can successfully control or impersonate a DNS server can   re-route traffic to subvert security protections.  For example,   routine traffic can be diverted to a compromised system to be   monitored; or, users can be tricked into providing authentication   secrets.  An organization should create well known, protected sitesFraser, Ed.                Informational                       [Page 17]

RFC 2196              Site Security Handbook              September 1997   to act as secondary name servers and protect their DNS masters from   denial of service attacks using filtering routers.   Traditionally, DNS has had no security capabilities. In particular,   the information returned from a query could not be checked for   modification or verified that it had come from the name server in   question.  Work has been done to incorporate digital signatures into   the protocol which, when deployed, will allow the integrity of the   information to be cryptographically verified (seeRFC 2065).3.2.3.2  Password/Key Servers (NIS(+) and KDC)   Password and key servers generally protect their vital information   (i.e., the passwords and keys) with encryption algorithms.  However,   even a one-way encrypted password can be determined by a dictionary   attack (wherein common words are encrypted to see if they match the   stored encryption).  It is therefore necessary to ensure that these   servers are not accessable by hosts which do not plan to use them for   the service, and even those hosts should only be able to access the   service (i.e., general services, such as Telnet and FTP, should not   be allowed by anyone other than administrators).3.2.3.3  Authentication/Proxy Servers (SOCKS, FWTK)   A proxy server provides a number of security enhancements.  It allows   sites to concentrate services through a specific host to allow   monitoring, hiding of internal structure, etc.  This funnelling of   services creates an attractive target for a potential intruder.  The   type of protection required for a proxy server depends greatly on the   proxy protocol in use and the services being proxied.  The general   rule of limiting access only to those hosts which need the services,   and limiting access by those hosts to only those services, is a good   starting point.3.2.3.4  Electronic Mail   Electronic mail (email) systems have long been a source for intruder   break-ins because email protocols are among the oldest and most   widely deployed services.  Also, by it's very nature, an email server   requires access to the outside world; most email servers accept input   from any source.  An email server generally consists of two parts: a   receiving/sending agent and a processing agent.  Since email is   delivered to all users, and is usually private, the processing agent   typically requires system (root) privileges to deliver the mail.   Most email implementations perform both portions of the service,   which means the receiving agent also has system privileges.  This   opens several security holes which this document will not describe.   There are some implementations available which allow a separation ofFraser, Ed.                Informational                       [Page 18]

RFC 2196              Site Security Handbook              September 1997   the two agents.  Such implementations are generally considered more   secure, but still require careful installation to avoid creating a   security problem.3.2.3.5  World Wide Web (WWW)   The Web is growing in popularity exponentially because of its ease of   use and the powerful ability to concentrate information services.   Most WWW servers accept some type of direction and action from the   persons accessing their services.  The most common example is taking   a request from a remote user and passing the provided information to   a program running on the server to process the request.  Some of   these programs are not written with security in mind and can create   security holes.  If a Web server is available to the Internet   community, it is especially important that confidential information   not be co-located on the same host as that server.  In fact, it is   recommended that the server have a dedicated host which is not   "trusted" by other internal hosts.   Many sites may want to co-locate FTP service with their WWW service.   But this should only occur for anon-ftp servers that only provide   information (ftp-get). Anon-ftp puts, in combination with WWW, might   be dangerous (e.g., they could result in modifications to the   information your site is publishing to the web) and in themselves   make the security considerations for each service different.3.2.3.6  File Transfer (FTP, TFTP)   FTP and TFTP both allow users to receive and send electronic files in   a point-to-point manner.  However, FTP requires authentication while   TFTP requires none. For this reason, TFTP should be avoided as much   as possible.   Improperly configured FTP servers can allow intruders to copy,   replace and delete files at will, anywhere on a host, so it is very   important to configure this service correctly.   Access to encrypted   passwords and proprietary data, and the introduction of Trojan horses   are just a few of the potential security holes that can occur when   the service is configured incorrectly. FTP servers should reside on   their own host.  Some sites choose to co-locate FTP with a Web   server, since the two protocols share common security considerations   However, the the practice isn't recommended, especially when the FTP   service allows the deposit of files (see section on WWW above). As   mentioned in the opening paragraphs ofsection 3.2.3, services   offered internally to your site should not be co-located with   services offered externally.  Each should have its own host.Fraser, Ed.                Informational                       [Page 19]

RFC 2196              Site Security Handbook              September 1997   TFTP does not support the same range of functions as FTP, and has no   security whatsoever.  This service should only be considered for   internal use, and then it should be configured in a restricted way so   that the server only has access to a set of predetermined files   (instead of every world-readable file on the system).  Probably the   most common usage of TFTP is for downloading router configuration   files to a router.  TFTP should reside on its own host, and should   not be installed on hosts supporting external FTP or Web access.3.2.3.7  NFS   The Network File Service allows hosts to share common disks.  NFS is   frequently used by diskless hosts who depend on a disk server for all   of their storage needs.  Unfortunately, NFS has no built-in security.   It is therefore necessary that the NFS server be accessable only by   those hosts which are using it for service.  This is achieved by   specifying which hosts the file system is being exported to and in   what manner (e.g., read-only, read-write, etc.). Filesystems should   not be exported to any hosts outside the local network since this   will require that the NFS service be accessible externally. Ideally,   external access to NFS service should be stopped by a firewall.3.2.4  Protecting the Protection   It is amazing how often a site will overlook the most obvious   weakness in its security by leaving the security server itself open   to attack.  Based on considerations previously discussed, it should   be clear that: the security server should not be accessible from   off-site; should offer minimum access, except for the authentication   function, to users on-site; and should not be co-located with any   other servers.  Further, all access to the node, including access to   the service itself, should be logged to provide a "paper trail" in   the event of a security breach.3.3  Firewalls   One of the most widely deployed and publicized security measures in   use on the Internet is a "firewall."  Firewalls have been given the   reputation of a general panacea for many, if not all, of the Internet   security issues.  They are not.  Firewalls are just another tool in   the quest for system security.  They provide a certain level of   protection and are, in general, a way of implementing security policy   at the network level.  The level of security that a firewall provides   can vary as much as the level of security on a particular machine.   There are the traditional trade-offs between security, ease of use,   cost, complexity, etc.Fraser, Ed.                Informational                       [Page 20]

RFC 2196              Site Security Handbook              September 1997   A firewall is any one of several mechanisms used to control and watch   access to and from a network for the purpose of protecting it.  A   firewall acts as a gateway through which all traffic to and from the   protected network and/or systems passes.  Firewalls help to place   limitations on the amount and type of communication that takes place   between the protected network and the another network (e.g., the   Internet, or another piece of the site's network).   A firewall is generally a way to build a wall between one part of a   network, a company's internal network, for example, and another part,   the global Internet, for example.  The unique feature about this wall   is that there needs to be ways for some traffic with particular   characteristics to pass through carefully monitored doors   ("gateways").  The difficult part is establishing the criteria by   which the packets are allowed or denied access through the doors.   Books written on firewalls use different terminology to describe the   various forms of firewalls. This can be confusing to system   administrators who are not familiar with firewalls. The thing to note   here is that there is no fixed terminology for the description of   firewalls.   Firewalls are not always, or even typically, a single machine.   Rather, firewalls are often a combination of routers, network   segments, and host computers.  Therefore, for the purposes of this   discussion, the term "firewall" can consist of more than one physical   device.  Firewalls are typically built using two different   components, filtering routers and proxy servers.   Filtering routers are the easiest component to conceptualize in a   firewall.  A router moves data back and forth between two (or more)   different networks.  A "normal" router takes a packet from network A   and "routes" it to its destination on network B.  A filtering router   does the same thing but decides not only how to route the packet, but   whether it should route the packet.  This is done by installing a   series of filters by which the router decides what to do with any   given packet of data.   A discussion concerning capabilities of a particular brand of router,   running a particular software version is outside the scope of this   document.  However, when evaluating a router to be used for filtering   packets, the following criteria can be important when implementing a   filtering policy:  source and destination IP address, source and   destination TCP port numbers, state of the TCP "ack" bit, UDP source   and destination port numbers, and direction of packet flow (i.e.. A-   >B or B->A).  Other information necessary to construct a secure   filtering scheme are whether the router reorders filter instructions   (designed to optimize filters, this can sometimes change the meaning   and cause unintended access), and whether it is possible to applyFraser, Ed.                Informational                       [Page 21]

RFC 2196              Site Security Handbook              September 1997   filters for inbound and outbound packets on each interface (if the   router filters only outbound packets then the router is "outside" of   its filters and may be more vulnerable to attack).  In addition to   the router being vulnerable, this distinction between applying   filters on inbound or outbound packets is especially relevant for   routers with more than 2 interfaces.  Other important issues are the   ability to create filters based on IP header options and the fragment   state of a packet.  Building a good filter can be very difficult and   requires a good understanding of the type of services (protocols)   that will be filtered.   For better security, the filters usually restrict access between the   two connected nets to just one host, the bastion host.  It is only   possible to access the other network via this bastion host.  As only   this host, rather than a few hundred hosts, can get attacked, it is   easier to maintain a certain level of security because only this host   has to be protected very carefully.  To make resources available to   legitimate users across this firewall, services have to be forwarded   by the bastion host.  Some servers have forwarding built in (like   DNS-servers or SMTP-servers), for other services (e.g., Telnet, FTP,   etc.), proxy servers can be used to allow access to the resources   across the firewall in a secure way.   A proxy server is way to concentrate application services through a   single machine.  There is typically a single machine (the bastion   host) that acts as a proxy server for a variety of protocols (Telnet,   SMTP, FTP, HTTP, etc.) but there can be individual host computers for   each service.  Instead of connecting directly to an external server,   the client connects to the proxy server which in turn initiates a   connection to the requested external server.  Depending on the type   of proxy server used, it is possible to configure internal clients to   perform this redirection automatically, without knowledge to the   user, others might require that the user connect directly to the   proxy server and then initiate the connection through a specified   format.   There are significant security benefits which can be derived from   using proxy servers.  It is possible to add access control lists to   protocols, requiring users or systems to provide some level of   authentication before access is granted.  Smarter proxy servers,   sometimes called Application Layer Gateways (ALGs), can be written   which understand specific protocols and can be configured to block   only subsections of the protocol.  For example, an ALG for FTP can   tell the difference between the "put" command and the "get" command;   an organization may wish to allow users to "get" files from the   Internet, but not be able to "put" internal files on a remote server.   By contrast, a filtering router could either block all FTP access, or   none, but not a subset.Fraser, Ed.                Informational                       [Page 22]

RFC 2196              Site Security Handbook              September 1997   Proxy servers can also be configured to encrypt data streams based on   a variety of parameters.  An organization might use this feature to   allow encrypted connections between two locations whose sole access   points are on the Internet.   Firewalls are typically thought of as a way to keep intruders out,   but they are also often used as a way to let legitimate users into a   site.  There are many examples where a valid user might need to   regularly access the "home" site while on travel to trade shows and   conferences, etc.  Access to the Internet is often available but may   be through an untrusted machine or network.  A correctly configured   proxy server can allow the correct users into the site while still   denying access to other users.   The current best effort in firewall techniques is found using a   combination of a pair of screening routers with one or more proxy   servers on a network between the two routers.  This setup allows the   external router to block off any attempts to use the underlying IP   layer to break security (IP spoofing, source routing, packet   fragments), while allowing the proxy server to handle potential   security holes in the higher layer protocols.  The internal router's   purpose is to block all traffic except to the proxy server.  If this   setup is rigidly implemented, a high level of security can be   achieved.   Most firewalls provide logging which can be tuned to make security   administration of the network more convenient.  Logging may be   centralized and the system may be configured to send out alerts for   abnormal conditions.  It is important to regularly monitor these logs   for any signs of intrusions or break-in attempts.  Since some   intruders will attempt to cover their tracks by editing logs, it is   desirable to protect these logs.  A variety of methods is available,   including: write once, read many (WORM) drives; papers logs; and   centralized logging via the "syslog" utility.  Another technique is   to use a "fake" serial printer, but have the serial port connected to   an isolated machine or PC which keeps the logs.   Firewalls are available in a wide range of quality and strengths.   Commercial packages start at approximately $10,000US and go up to   over $250,000US.  "Home grown" firewalls can be built for smaller   amounts of capital.  It should be remembered that the correct setup   of a firewall (commercial or homegrown) requires a significant amount   of skill and knowledge of TCP/IP.  Both types require regular   maintenance, installation of software patches and updates, and   regular monitoring.  When budgeting for a firewall, these additional   costs should be considered in addition to the cost of the physical   elements of the firewall.Fraser, Ed.                Informational                       [Page 23]

RFC 2196              Site Security Handbook              September 1997   As an aside, building a "home grown" firewall requires a significant   amount of skill and knowledge of TCP/IP.  It should not be trivially   attempted because a perceived sense of security is worse in the long   run than knowing that there is no security.  As with all security   measures, it is important to decide on the threat, the value of the   assets to be protected, and the costs to implement security.   A final note about firewalls.  They can be a great aid when   implementing security for a site and they protect against a large   variety of attacks.  But it is important to keep in mind that they   are only one part of the solution.  They cannot protect your site   against all types of attack.4.  Security Services and Procedures   This chapter guides the reader through a number of topics that should   be addressed when securing a site.  Each section touches on a   security service or capability that may be required to protect the   information and systems at a site.  The topics are presented at a   fairly high-level to introduce the reader to the concepts.   Throughout the chapter, you will find significant mention of   cryptography.  It is outside the scope of this document to delve into   details concerning cryptography, but the interested reader can obtain   more information from books and articles listed in the reference   section of this document.4.1  Authentication   For many years, the prescribed method for authenticating users has   been through the use of standard, reusable passwords.  Originally,   these passwords were used by users at terminals to authenticate   themselves to a central computer.  At the time, there were no   networks (internally or externally), so the risk of disclosure of the   clear text password was minimal.  Today, systems are connected   together through local networks, and these local networks are further   connected together and to the Internet.  Users are logging in from   all over the globe; their reusable passwords are often transmitted   across those same networks in clear text, ripe for anyone in-between   to capture.  And indeed, the CERT* Coordination Center and other   response teams are seeing a tremendous number of incidents involving   packet sniffers which are capturing the clear text passwords.   With the advent of newer technologies like one-time passwords (e.g.,   S/Key), PGP, and token-based authentication devices, people are using   password-like strings as secret tokens and pins.  If these secret   tokens and pins are not properly selected and protected, the   authentication will be easily subverted.Fraser, Ed.                Informational                       [Page 24]

RFC 2196              Site Security Handbook              September 19974.1.1  One-Time passwords   As mentioned above, given today's networked environments, it is   recommended that sites concerned about the security and integrity of   their systems and networks consider moving away from standard,   reusable passwords.  There have been many incidents involving Trojan   network programs (e.g., telnet and rlogin) and network packet   sniffing programs.  These programs capture clear text   hostname/account name/password triplets.  Intruders can use the   captured information for subsequent access to those hosts and   accounts.  This is possible because 1) the password is used over and   over (hence the term "reusable"), and 2) the password passes across   the network in clear text.   Several authentication techniques have been developed that address   this problem.  Among these techniques are challenge-response   technologies that provide passwords that are only used once (commonly   called one-time passwords). There are a number of products available   that sites should consider using. The decision to use a product is   the responsibility of each organization, and each organization should   perform its own evaluation and selection.4.1.2  Kerberos   Kerberos is a distributed network security system which provides for   authentication across unsecured networks.  If requested by the   application, integrity and encryption can also be provided.  Kerberos   was originally developed at the Massachusetts Institute of Technology   (MIT) in the mid 1980s.  There are two major releases of Kerberos,   version 4 and 5, which are for practical purposes, incompatible.   Kerberos relies on a symmetric key database using a key distribution   center (KDC) which is known as the Kerberos server.  A user or   service (known as "principals") are granted electronic "tickets"   after properly communicating with the KDC.  These tickets are used   for authentication between principals.  All tickets include a time   stamp which limits the time period for which the ticket is valid.   Therefore, Kerberos clients and server must have a secure time   source, and be able to keep time accurately.   The practical side of Kerberos is its integration with the   application level.  Typical applications like FTP, telnet, POP, and   NFS have been integrated with the Kerberos system.  There are a   variety of implementations which have varying levels of integration.   Please see the Kerberos FAQ available athttp://www.ov.com/misc/krb-faq.html for the latest information.Fraser, Ed.                Informational                       [Page 25]

RFC 2196              Site Security Handbook              September 19974.1.3  Choosing and Protecting Secret Tokens and PINs   When selecting secret tokens, take care to choose them carefully.   Like the selection of passwords, they should be robust against brute   force efforts to guess them.  That is, they should not be single   words in any language, any common, industry, or cultural acronyms,   etc.  Ideally, they will be longer rather than shorter and consist of   pass phrases that combine upper and lower case character, digits, and   other characters.   Once chosen, the protection of these secret tokens is very important.   Some are used as pins to hardware devices (like token cards) and   these should not be written down or placed in the same location as   the device with which they are associated.  Others, such as a secret   Pretty Good Privacy (PGP) key, should be protected from unauthorized   access.   One final word on this subject.  When using cryptography products,   like PGP, take care to determine the proper key length and ensure   that your users are trained to do likewise.  As technology advances,   the minimum safe key length continues to grow.  Make sure your site   keeps up with the latest knowledge on the technology so that you can   ensure that any cryptography in use is providing the protection you   believe it is.4.1.4  Password Assurance   While the need to eliminate the use of standard, reusable passwords   cannot be overstated, it is  recognized that some organizations may   still be using them.  While it's recommended that these organizations   transition to the use of better technology, in the mean time, we have   the following advice to help with the selection and maintenance of   traditional passwords. But remember, none of these measures provides   protection against disclosure due to sniffer programs.   (1)  The importance of robust passwords - In many (if not most) cases        of system penetration, the intruder needs to gain access to an        account on the system. One way that goal is typically        accomplished is through guessing the password of a legitimate        user.  This is often accomplished by running an automated        password cracking program, which utilizes a very large        dictionary, against the system's password file.  The only way to        guard against passwords being disclosed in this manner is        through the careful selection of passwords which cannot be        easily guessed (i.e., combinations of numbers, letters, and        punctuation characters).  Passwords should also be as long as        the system supports and users can tolerate.Fraser, Ed.                Informational                       [Page 26]

RFC 2196              Site Security Handbook              September 1997   (2)  Changing default passwords - Many operating systems and        application programs are installed with default accounts and        passwords.  These must be changed immediately to something that        cannot be guessed or cracked.   (3)  Restricting access to the password file - In particular, a site        wants to protect the encrypted password portion of the file so        that would-be intruders don't have them available for cracking.        One effective technique is to use shadow passwords where the        password field of the standard file contains a dummy or false        password.  The file containing the legitimate passwords are        protected elsewhere on the system.   (4)  Password aging - When and how to expire passwords is still a        subject of controversy among the security community.  It is        generally accepted that a password should not be maintained once        an account is no longer in use, but it is hotly debated whether        a user should be forced to change a good password that's in        active use.  The arguments for changing passwords relate to the        prevention of the continued use of penetrated accounts.        However, the opposition claims that frequent password changes        lead to users writing down their passwords in visible areas        (such as pasting them to a terminal), or to users selecting very        simple passwords that are easy to guess.  It should also be        stated that an intruder will probably use a captured or guessed        password sooner rather than later, in which case password aging        provides little if any protection.        While there is no definitive answer to this dilemma, a password        policy should directly address the issue and provide guidelines        for how often a user should change the password.  Certainly, an        annual change in their password is usually not difficult for        most users, and you should consider requiring it.  It is        recommended that passwords be changed at least whenever a        privileged account is compromised, there is a critical change in        personnel (especially if it is an administrator!), or when an        account has been compromised.  In addition, if a privileged        account password is compromised, all passwords on the system        should be changed.   (5)  Password/account blocking - Some sites find it useful to disable        accounts after a predefined number of failed attempts to        authenticate.  If your site decides to employ this mechanism, it        is recommended that the mechanism not "advertise" itself. AfterFraser, Ed.                Informational                       [Page 27]

RFC 2196              Site Security Handbook              September 1997        disabling, even if the correct password is presented, the        message displayed should remain that of a failed login attempt.        Implementing this mechanism will require that legitimate users        contact their system administrator to request that their account        be reactivated.   (6)  A word about the finger daemon - By default, the finger daemon        displays considerable system and user information. For example,        it can display a list of all users currently using a system, or        all the contents of a specific user's .plan file.  This        information can be used by would-be intruders to identify        usernames and guess their passwords. It is recommended that        sites consider modifying finger to restrict the information        displayed.4.2  Confidentiality   There will be information assets that your site will want to protect   from disclosure to unauthorized entities.  Operating systems often   have built-in file protection mechanisms that allow an administrator   to control who on the system can access, or "see," the contents of a   given file.  A stronger way to provide confidentiality is through   encryption.  Encryption is accomplished by scrambling data so that it   is very difficult and time consuming for anyone other than the   authorized recipients or owners to obtain the plain text.  Authorized   recipients and the owner of the information will possess the   corresponding decryption keys that allow them to easily unscramble   the text to a readable (clear text) form.  We recommend that sites   use encryption to provide confidentiality and protect valuable   information.   The use of encryption is sometimes controlled by governmental and   site regulations, so we encourage administrators to become informed   of laws or policies that regulate its use before employing it.  It is   outside the scope of this document to discuss the various algorithms   and programs available for this purpose, but we do caution against   the casual use of the UNIX crypt program as it has been found to be   easily broken.  We also encourage everyone to take time to understand   the strength of the encryption in any given algorithm/product before   using it.  Most well-known products are well-documented in the   literature, so this should be a fairly easy task.4.3  Integrity   As an administrator, you will want to make sure that information   (e.g., operating system files, company data, etc.) has not been   altered in an unauthorized fashion.  This means you will want to   provide some assurance as to the integrity of the information on yourFraser, Ed.                Informational                       [Page 28]

RFC 2196              Site Security Handbook              September 1997   systems.  One way to provide this is to produce a checksum of the   unaltered file, store that checksum offline, and periodically (or   when desired) check to make sure the checksum of the online file   hasn't changed (which would indicate the data has been modified).   Some operating systems come with checksumming programs, such as the   UNIX sum program.  However, these may not provide the protection you   actually need.  Files can be modified in such a way as to preserve   the result of the UNIX sum program!  Therefore, we suggest that you   use a cryptographically strong program, such as the message digesting   program MD5 [ref], to produce the checksums you will be using to   assure integrity.   There are other applications where integrity will need to be assured,   such as when transmitting an email message between two parties. There   are products available that can provide this capability.  Once you   identify that this is a capability you need, you can go about   identifying technologies that will provide it.4.4  Authorization   Authorization refers to the process of granting privileges to   processes and, ultimately, users.  This differs from authentication   in that authentication is the process used to identify a user.  Once   identified (reliably), the privileges, rights, property, and   permissible actions of the user are determined by authorization.   Explicitly listing the authorized activities of each user (and user   process) with respect to all resources (objects) is impossible in a   reasonable system.  In a real system certain techniques are used to   simplify the process of granting and checking authorization(s).   One approach, popularized in UNIX systems, is to assign to each   object three classes of user: owner, group and world.  The owner is   either the creator of the object or the user assigned as owner by the   super-user.  The owner permissions (read, write and execute) apply   only to the owner.  A group is a collection of users which share   access rights to an object.  The group permissions (read, write and   execute) apply to all users in the group (except the owner).  The   world refers to everybody else with access to the system.  The world   permissions (read, write and execute) apply to all users (except the   owner and members of the group).   Another approach is to attach to an object a list which explicitly   contains the identity of all permitted users (or groups).  This is an   Access Control List (ACL).  The advantage of ACLs are that they areFraser, Ed.                Informational                       [Page 29]

RFC 2196              Site Security Handbook              September 1997   easily maintained (one central list per object) and it's very easy to   visually check who has access to what. The disadvantages are the   extra resources required to store such lists, as well as the vast   number of such lists required for large systems.4.5  Access4.5.1  Physical Access   Restrict physical access to hosts, allowing access only to those   people who are supposed to use the hosts.  Hosts include "trusted"   terminals (i.e., terminals which allow unauthenticated use such as   system consoles, operator terminals and terminals dedicated to   special tasks), and individual microcomputers and workstations,   especially those connected to your network.  Make sure people's work   areas mesh well with access restrictions; otherwise they will find   ways to circumvent your physical security (e.g., jamming doors open).   Keep original and backup copies of data and programs safe.  Apart   from keeping them in good condition for backup purposes, they must be   protected from theft.  It is important to keep backups in a separate   location from the originals, not only for damage considerations, but   also to guard against thefts.   Portable hosts are a particular risk.  Make sure it won't cause   problems if one of your staff's portable computer is stolen.   Consider developing guidelines for the kinds of data that should be   allowed to reside on the disks of portable computers as well as how   the data should be protected (e.g., encryption) when it is on a   portable computer.   Other areas where physical access should be restricted is the wiring   closets and important network elements like file servers, name server   hosts, and routers.4.5.2  Walk-up Network Connections   By "walk-up" connections, we mean network connection points located   to provide a convenient way for users to connect a portable host to   your network.   Consider whether you need to provide this service, bearing in mind   that it allows any user to attach an unauthorized host to your   network.  This increases the risk of attacks via techniques such asFraser, Ed.                Informational                       [Page 30]

RFC 2196              Site Security Handbook              September 1997   IP address spoofing, packet sniffing, etc.  Users and site management   must appreciate the risks involved.  If you decide to provide walk-up   connections, plan the service carefully and define precisely where   you will provide it so that you can ensure the necessary physical   access security.   A walk-up host should be authenticated before its user is permitted   to access resources on your network.  As an alternative, it may be   possible to control physical access. For example, if the service is   to be used by students, you might only provide walk-up connection   sockets in student laboratories.   If you are providing walk-up access for visitors to connect back to   their home networks (e.g., to read e-mail, etc.) in your facility,   consider using a separate subnet that has no connectivity to the   internal network.   Keep an eye on any area that contains unmonitored access to the   network, such as vacant offices.  It may be sensible to disconnect   such areas at the wiring closet, and consider using secure hubs and   monitoring attempts to connect unauthorized hosts.4.5.3  Other Network Technologies   Technologies considered here include X.25, ISDN, SMDS, DDS and Frame   Relay.  All are provided via physical links which go through   telephone exchanges, providing the potential for them to be diverted.   Crackers are certainly interested in telephone switches as well as in   data networks!   With switched technologies, use Permanent Virtual Circuits or Closed   User Groups whenever this is possible.  Technologies which provide   authentication and/or encryption (such as IPv6) are evolving rapidly;   consider using them on links where security is important.4.5.4  Modems4.5.4.1  Modem Lines Must Be Managed   Although they provide convenient access to a site for its users, they   can also provide an effective detour around the site's firewalls.   For this reason it is essential to maintain proper control of modems.   Don't allow users to install a modem line without proper   authorization.  This includes temporary installations (e.g., plugging   a modem into a facsimile or telephone line overnight).Fraser, Ed.                Informational                       [Page 31]

RFC 2196              Site Security Handbook              September 1997   Maintain a register of all your modem lines and keep your register up   to date.  Conduct regular (ideally automated) site checks for   unauthorized modems.4.5.4.2  Dial-in Users Must Be Authenticated   A username and password check should be completed before a user can   access anything on your network.  Normal password security   considerations are particularly important (seesection 4.1.1).   Remember that telephone lines can be tapped, and that it is quite   easy to intercept messages to cellular phones.  Modern high-speed   modems use more sophisticated modulation techniques, which makes them   somewhat more difficult to monitor, but it is prudent to assume that   hackers know how to eavesdrop on your lines.  For this reason, you   should use one-time passwords if at all possible.   It is helpful to have a single dial-in point (e.g., a single large   modem pool) so that all users are authenticated in the same way.   Users will occasionally mis-type a password.  Set a short delay - say   two seconds - after the first and second failed logins, and force a   disconnect after the third.  This will slow down automated password   attacks.  Don't tell the user whether the username, the password, or   both, were incorrect.4.5.4.3  Call-back Capability   Some dial-in servers offer call-back facilities (i.e., the user dials   in and is authenticated, then the system disconnects the call and   calls back on a specified number).  Call-back is useful since if   someone were to guess a username and password, they are disconnected,   and the system then calls back the actual user whose password was   cracked; random calls from a server are suspicious, at best.  This   does mean users may only log in from one location (where the server   is configured to dial them back), and of course there may be phone   charges associated with there call-back location.   This feature should be used with caution; it can easily be bypassed.   At a minimum, make sure that the return call is never made from the   same modem as the incoming one.  Overall, although call-back can   improve modem security, you should not depend on it alone.4.5.4.4  All Logins Should Be Logged   All logins, whether successful or unsuccessful should be logged.   However, do not keep correct passwords in the log. Rather, log them   simply as a successful login attempt.  Since most bad passwords areFraser, Ed.                Informational                       [Page 32]

RFC 2196              Site Security Handbook              September 1997   mistyped by authorized users, they only vary by a single character   from the actual password.  Therefore if you can't keep such a log   secure, don't log it at all.   If Calling Line Identification is available, take advantage of it by   recording the calling number for each login attempt.  Be sensitive to   the privacy issues raised by Calling Line Identification.  Also be   aware that Calling Line Identification is not to be trusted (since   intruders have been known to break into phone switches and forward   phone numbers or make other changes); use the data for informational   purposes only, not for authentication.4.5.4.5  Choose Your Opening Banner Carefully   Many sites use a system default contained in a message of the day   file for their opening banner. Unfortunately, this often includes the   type of host hardware or operating system present on the host.  This   can provide valuable information to a would-be intruder. Instead,   each site should create its own specific login banner, taking care to   only include necessary information.   Display a short banner, but don't offer an "inviting" name (e.g.,   University of XYZ, Student Records System).  Instead, give your site   name, a short warning that sessions may be monitored, and a   username/password prompt.  Verify possible legal issues related to   the text you put into the banner.   For high-security applications, consider using a "blind" password   (i.e., give no response to an incoming call until the user has typed   in a password).  This effectively simulates a dead modem.4.5.4.6  Dial-out Authentication   Dial-out users should also be authenticated, particularly since your   site will have to pay their telephone charges.   Never allow dial-out from an unauthenticated dial-in call, and   consider whether you will allow it from an authenticated one.  The   goal here is to prevent callers using your modem pool as part of a   chain of logins.  This can be hard to detect, particularly if a   hacker sets up a path through several hosts on your site.   At a minimum, don't allow the same modems and phone lines to be used   for both dial-in and dial-out.  This can be implemented easily if you   run separate dial-in and dial-out modem pools.Fraser, Ed.                Informational                       [Page 33]

RFC 2196              Site Security Handbook              September 19974.5.4.7  Make Your Modem Programming as "Bullet-proof" as Possible   Be sure modems can't be reprogrammed while they're in service.  At a   minimum, make sure that three plus signs won't put your dial-in   modems into command mode!   Program your modems to reset to your standard configuration at the   start of each new call.  Failing this, make them reset at the end of   each call.  This precaution will protect you against accidental   reprogramming of your modems. Resetting at both the end and the   beginning of each call will assure an even higher level of confidence   that a new caller will not inherit a previous caller's session.   Check that your modems terminate calls cleanly.  When a user logs out   from an access server, verify that the server hangs up the phone line   properly.  It is equally important that the server forces logouts   from whatever sessions were active if the user hangs up unexpectedly.4.6  Auditing   This section covers the procedures for collecting data generated by   network activity, which may be useful in analyzing the security of a   network and responding to security incidents.4.6.1  What to Collect   Audit data should include any attempt to achieve a different security   level by any person, process, or other entity in the network.  This   includes login and logout, super user access (or the non-UNIX   equivalent), ticket generation (for Kerberos, for example), and any   other change of access or status.  It is especially important to note   "anonymous" or "guest" access to public servers.   The actual data to collect will differ for different sites and for   different types of access changes within a site.  In general, the   information you want to collect includes: username and hostname, for   login and logout; previous and new access rights, for a change of   access rights; and a timestamp.  Of course, there is much more   information which might be gathered, depending on what the system   makes available and how much space is available to store that   information.   One very important note: do not gather passwords.  This creates an   enormous potential security breach if the audit records should be   improperly accessed.  Do not gather incorrect passwords either, as   they often differ from valid passwords by only a single character or   transposition.Fraser, Ed.                Informational                       [Page 34]

RFC 2196              Site Security Handbook              September 19974.6.2  Collection Process   The collection process should be enacted by the host or resource   being accessed.  Depending on the importance of the data and the need   to have it local in instances in which services are being denied,   data could be kept local to the resource until needed or be   transmitted to storage after each event.   There are basically three ways to store audit records: in a   read/write file on a host, on a write-once/read-many device (e.g., a   CD-ROM or a specially configured tape drive), or on a write-only   device (e.g., a line printer).  Each method has advantages and   disadvantages.   File system logging is the least resource intensive of the three   methods and the easiest to configure.  It allows instant access to   the records for analysis, which may be important if an attack is in   progress.  File system logging is also the least reliable method.  If   the logging host has been compromised, the file system is usually the   first thing to go; an intruder could easily cover up traces of the   intrusion.   Collecting audit data on a write-once device is slightly more effort   to configure than a simple file, but it has the significant advantage   of greatly increased security because an intruder could not alter the   data showing that an intrusion has occurred.  The disadvantage of   this method is the need to maintain a supply of storage media and the   cost of that media.  Also, the data may not be instantly available.   Line printer logging is useful in system where permanent and   immediate logs are required.  A real time system is an example of   this, where the exact point of a failure or attack must be recorded.   A laser printer, or other device which buffers data (e.g., a print   server), may suffer from lost data if buffers contain the needed data   at a critical instant.  The disadvantage of, literally, "paper   trails" is the need to keep the printer fed and the need to scan   records by hand.  There is also the issue of where to store the,   potentially, enormous volume of paper which may be generated.   For each of the logging methods described, there is also the issue of   securing the path between the device generating the log and actual   logging device (i.e., the file server, tape/CD-ROM drive, printer).   If that path is compromised, logging can be stopped or spoofed or   both.  In an ideal world, the logging device would be directlyFraser, Ed.                Informational                       [Page 35]

RFC 2196              Site Security Handbook              September 1997   attached by a single, simple, point-to-point cable.  Since that is   usually impractical, the path should pass through the minimum number   of networks and routers.  Even if logs can be blocked, spoofing can   be prevented with cryptographic checksums (it probably isn't   necessary to encrypt the logs because they should not contain   sensitive information in the first place).4.6.3  Collection Load   Collecting audit data may result in a rapid accumulation of bytes so   storage availability for this information must be considered in   advance.  There are a few ways to reduce the required storage space.   First, data can be compressed, using one of many methods. Or, the   required space can be minimized by keeping data for a shorter period   of time with only summaries of that data kept in long-term archives.   One major drawback to the latter method involves incident response.   Often, an incident has been ongoing for some period of time when a   site notices it and begins to investigate. At that point in time,   it's very helpful to have detailed audit logs available. If these are   just summaries, there may not be sufficient detail to fully handle   the incident.4.6.4  Handling and Preserving Audit Data   Audit data should be some of the most carefully secured data at the   site and in the backups.  If an intruder were to gain access to audit   logs, the systems themselves, in addition to the data, would be at   risk.   Audit data may also become key to the investigation, apprehension,   and prosecution of the perpetrator of an incident.  For this reason,   it is advisable to seek the advice of legal council when deciding how   audit data should be treated.  This should happen before an incident   occurs.   If a data handling plan is not adequately defined prior to an   incident, it may mean that there is no recourse in the aftermath of   an event, and it may create liability resulting from improper   treatment of the data.4.6.5  Legal Considerations   Due to the content of audit data, there are a number of legal   questions that arise which might need to be addressed by your legal   counsel. If you collect and save audit data, you need to be prepared   for consequences resulting both from its existence and its content.Fraser, Ed.                Informational                       [Page 36]

RFC 2196              Site Security Handbook              September 1997   One area concerns the privacy of individuals.  In certain instances,   audit data may contain personal information.  Searching through the   data, even for a routine check of the system's security, could   represent an invasion of privacy.   A second area of concern involves knowledge of intrusive behavior   originating from your site.  If an organization keeps audit data, is   it responsible for examining it to search for incidents?  If a host   in one organization is used as a launching point for an attack   against another organization, can the second organization use the   audit data of the first organization to prove negligence on the part   of that organization?   The above examples are meant to be comprehensive, but should motivate   your organization to consider the legal issues involved with audit   data.4.7  Securing Backups   The procedure of creating backups is a classic part of operating a   computer system.  Within the context of this document, backups are   addressed as part of the overall security plan of a site.  There are   several aspects to backups that are important within this context:   (1)  Make sure your site is creating backups   (2)  Make sure your site is using offsite storage for backups. The        storage site should be carefully selected for both its security        and its availability.   (3)  Consider encrypting your backups to provide additional protection        of the information once it is off-site.  However, be aware that        you will need a good key management scheme so that you'll be        able to recover data at any point in the future.  Also, make        sure you will have access to the necessary decryption programs        at such time in the future as you need to perform the        decryption.   (4)  Don't always assume that your backups are good.  There have been        many instances of computer security incidents that have gone on        for long periods of time before a site has noticed the incident.        In such cases, backups of the affected systems are also tainted.   (5)  Periodically verify the correctness and completeness of your        backups.5.  Security Incident Handling   This chapter of the document will supply guidance to be used before,   during, and after a computer security incident occurs on a host,   network, site, or multi-site environment.  The operative philosophy   in the event of a breach of computer security is to react accordingFraser, Ed.                Informational                       [Page 37]

RFC 2196              Site Security Handbook              September 1997   to a plan.  This is true whether the breach is the result of an   external intruder attack, unintentional damage, a student testing   some new program to exploit a software vulnerability, or a   disgruntled employee.  Each of the possible types of events, such as   those just listed, should be addressed in advance by adequate   contingency plans.   Traditional computer security, while quite important in the overall   site security plan, usually pays little attention to how to actually   handle an attack once one occurs.  The result is that when an attack   is in progress, many decisions are made in haste and can be damaging   to tracking down the source of the incident, collecting evidence to   be used in prosecution efforts, preparing for the recovery of the   system, and protecting the valuable data contained on the system.   One of the most important, but often overlooked, benefits for   efficient incident handling is an economic one.  Having both   technical and managerial personnel respond to an incident requires   considerable resources.  If trained to handle incidents efficiently,   less staff time is required when one occurs.   Due to the world-wide network most incidents are not restricted to a   single site.  Operating systems vulnerabilities apply (in some cases)   to several millions of systems, and many vulnerabilities are   exploited within the network itself.  Therefore, it is vital that all   sites with involved parties be informed as soon as possible.   Another benefit is related to public relations.  News about computer   security incidents tends to be damaging to an organization's stature   among current or potential clients.  Efficient incident handling   minimizes the potential for negative exposure.   A final benefit of efficient incident handling is related to legal   issues.  It is possible that in the near future organizations may be   held responsible because one of their nodes was used to launch a   network attack.   In a similar vein, people who develop patches or   workarounds may be sued if the patches or workarounds are   ineffective, resulting in compromise of the systems, or, if the   patches or workarounds themselves damage systems.  Knowing about   operating system vulnerabilities and patterns of attacks, and then   taking appropriate measures to counter these potential threats, is   critical to circumventing possible legal problems.Fraser, Ed.                Informational                       [Page 38]

RFC 2196              Site Security Handbook              September 1997   The sections in this chapter provide an outline and starting point   for creating your site's policy for handling security incidents.  The   sections are:   (1)  Preparing and planning (what are the goals and objectives in        handling an incident).   (2)  Notification (who should be contacted in the case of an        incident).          - Local managers and personnel          - Law enforcement and investigative agencies          - Computer security incidents handling teams          - Affected and involved sites          - Internal communications          - Public relations and press releases   (3)  Identifying an incident (is it an incident and how serious is        it).   (4)  Handling (what should be done when an incident occurs).          - Notification (who should be notified about the incident)          - Protecting evidence and activity logs (what records should be            kept from before, during, and after the incident)          - Containment (how can the damage be limited)          - Eradication (how to eliminate the reasons for the incident)          - Recovery (how to reestablish service and systems)          - Follow Up (what actions should be taken after the incident)   (5)  Aftermath (what are the implications of past incidents).   (6)  Administrative response to incidents.   The remainder of this chapter will detail the issues involved in each   of the important topics listed above, and provide some guidance as to   what should be included in a site policy for handling incidents.5.1  Preparing and Planning for Incident Handling   Part of handling an incident is being prepared to respond to an   incident before the incident occurs in the first place.  This   includes establishing a suitable level of protections as explained in   the preceding chapters.  Doing this should help your site prevent   incidents as well as limit potential damage resulting from them when   they do occur.  Protection also includes preparing incident handling   guidelines as part of a contingency plan for your organization or   site.  Having written plans eliminates much of the ambiguity which   occurs during an incident, and will lead to a more appropriate and   thorough set of responses.  It is vitally important to test the   proposed plan before an incident occurs through "dry runs".  A team   might even consider hiring a tiger team to act in parallel with the   dry run.  (Note: a tiger team is a team of specialists that try to   penetrate the security of a system.)Fraser, Ed.                Informational                       [Page 39]

RFC 2196              Site Security Handbook              September 1997   Learning to respond efficiently to an incident is important for a   number of reasons:   (1)  Protecting the assets which could be compromised   (2)  Protecting resources which could be utilized more        profitably if an incident did not require their services   (3)  Complying with (government or other) regulations   (4)  Preventing the use of your systems in attacks against other        systems (which could cause you to incur legal liability)   (5)  Minimizing the potential for negative exposure   As in any set of pre-planned procedures, attention must be paid to a   set of goals for handling an incident.  These goals will be   prioritized differently depending on the site.  A specific set of   objectives can be identified for dealing with incidents:   (1)  Figure out how it happened.   (2)  Find out how to avoid further exploitation of the same          vulnerability.   (3)  Avoid escalation and further incidents.   (4)  Assess the impact and damage of the incident.   (5)  Recover from the incident.   (6)  Update policies and procedures as needed.   (7)  Find out who did it (if appropriate and possible).   Due to the nature of the incident, there might be a conflict between   analyzing the original source of a problem and restoring systems and   services.  Overall goals (like assuring the integrity of critical   systems) might be the reason for not analyzing an incident.  Of   course, this is an important management decision; but all involved   parties must be aware that without analysis the same incident may   happen again.   It is also important to prioritize the actions to be taken during an   incident well in advance of the time an incident occurs.  Sometimes   an incident may be so complex that it is impossible to do everything   at once to respond to it; priorities are essential.  Although   priorities will vary from institution to institution, the following   suggested priorities may serve as a starting point for defining your   organization's response:   (1)  Priority one -- protect human life and people's        safety; human life always has precedence over all        other considerations.   (2)  Priority two -- protect classified and/or sensitive        data.  Prevent exploitation of classified and/or        sensitive systems, networks or sites.  Inform affectedFraser, Ed.                Informational                       [Page 40]

RFC 2196              Site Security Handbook              September 1997        classified and/or sensitive systems, networks or sites        about already occurred penetrations.        (Be aware of regulations by your site or by government)   (3)  Priority three -- protect other data, including        proprietary, scientific, managerial and other data,        because loss of data is costly in terms of resources.        Prevent exploitations of other systems, networks or        sites and inform already affected systems, networks or        sites about successful penetrations.   (4)  Priority four -- prevent damage to systems (e.g., loss        or alteration of system files, damage to disk drives,        etc.).  Damage to systems can result in costly down        time and recovery.   (5)  Priority five -- minimize disruption of computing        resources (including processes).  It is better in many        cases to shut a system down or disconnect from a network        than to risk damage to data or systems. Sites will have        to evaluate the trade-offs between shutting down and        disconnecting, and staying up. There may be service        agreements in place that may require keeping systems        up even in light of further damage occurring. However,        the damage and scope of an incident may be so extensive        that service agreements may have to be over-ridden.   An important implication for defining priorities is that once human   life and national security considerations have been addressed, it is   generally more important to save data than system software and   hardware.  Although it is undesirable to have any damage or loss   during an incident, systems can be replaced. However, the loss or   compromise of data (especially classified or proprietary data) is   usually not an acceptable outcome under any circumstances.   Another important concern is the effect on others, beyond the systems   and networks where the incident occurs.  Within the limits imposed by   government regulations it is always important to inform affected   parties as soon as possible.  Due to the legal implications of this   topic, it should be included in the planned procedures to avoid   further delays and uncertainties for the administrators.   Any plan for responding to security incidents should be guided by   local policies and regulations.  Government and private sites that   deal with classified material have specific rules that they must   follow.Fraser, Ed.                Informational                       [Page 41]

RFC 2196              Site Security Handbook              September 1997   The policies chosen by your site on how it reacts to incidents will   shape your response.  For example, it may make little sense to create   mechanisms to monitor and trace intruders if your site does not plan   to take action against the intruders if they are caught.  Other   organizations may have policies that affect your plans.  Telephone   companies often release information about telephone traces only to   law enforcement agencies.   Handling incidents can be tedious and require any number of routine   tasks that could be handled by support personnel. To free the   technical staff it may be helpful to identify support staff who will   help with tasks like: photocopying, fax'ing, etc.5.2  Notification and Points of Contact   It is important to establish contacts with various personnel before a   real incident occurs.  Many times, incidents are not real   emergencies. Indeed, often you will be able to handle the activities   internally. However, there will also be many times when others   outside your immediate department will need to be included in the   incident handling.  These additional contacts include local managers   and system administrators, administrative contacts for other sites on   the Internet, and various investigative organizations.  Getting to   know these contacts before incidents occurs will help to make your   incident handling process more efficient.   For each type of communication contact, specific "Points of Contact"   (POC) should be defined.  These may be technical or administrative in   nature and may include legal or investigative agencies as well as   service providers and vendors.  When establishing these contact, it   is important to decide how much information will be shared with each   class of contact. It is especially important to define, ahead of   time, what information will be shared with the users at a site, with   the public (including the press), and with other sites.   Settling these issues are especially important for the local person   responsible for handling the incident, since that is the person   responsible for the actual notification of others.  A list of   contacts in each of these categories is an important time saver for   this person during an incident.  It can be quite difficult to find an   appropriate person during an incident when many urgent events are   ongoing.  It is strongly recommended that all relevant telephone   numbers (also electronic mail addresses and fax numbers) be included   in the site security policy.  The names and contact information of   all individuals who will be directly involved in the handling of an   incident should be placed at the top of this list.Fraser, Ed.                Informational                       [Page 42]

RFC 2196              Site Security Handbook              September 19975.2.1  Local Managers and Personnel   When an incident is under way, a major issue is deciding who is in   charge of coordinating the activity of the multitude of players.  A   major mistake that can be made is to have a number of people who are   each working independently, but are not working together.  This will   only add to the confusion of the event and will probably lead to   wasted or ineffective effort.   The single POC may or may not be the person responsible for handling   the incident.  There are two distinct roles to fill when deciding who   shall be the POC and who will be the person in charge of the   incident.  The person in charge of the incident will make decisions   as to the interpretation of policy applied to the event.  In   contrast, the POC must coordinate the effort of all the parties   involved with handling the event.   The POC must be a person with the technical expertise to successfully   coordinate the efforts of the system managers and users involved in   monitoring and reacting to the attack. Care should be taken when   identifying who this person will be.  It should not necessarily be   the same person who has administrative responsibility for the   compromised systems since often such administrators have knowledge   only sufficient for the day to day use of the computers, and lack in   depth technical expertise.   Another important function of the POC is to maintain contact with law   enforcement and other external agencies to assure that multi-agency   involvement occurs.  The level of involvement will be determined by   management decisions as well as legal constraints.   A single POC should also be the single person in charge of collecting   evidence, since as a rule of thumb, the more people that touch a   potential piece of evidence, the greater the possibility that it will   be inadmissible in court. To ensure that evidence will be acceptable   to the legal community, collecting evidence should be done following   predefined procedures in accordance with local laws and legal   regulations.   One of the most critical tasks for the POC is the coordination of all   relevant processes.  Responsibilities may be distributed over the   whole site, involving multiple independent departments or groups.   This will require a  well coordinated effort in order to achieve   overall success.  The situation becomes even more complex if multiple   sites are involved.  When this happens, rarely will a single POC at   one site be able to adequately coordinate the handling of the entire   incident.  Instead, appropriate incident response teams should be   involved.Fraser, Ed.                Informational                       [Page 43]

RFC 2196              Site Security Handbook              September 1997   The incident handling process should provide some escalation   mechanisms.  In order to define such a mechanism, sites will need to   create an internal classification scheme for incidents. Associated   with each level of incident will be the appropriate POC and   procedures.  As an incident is escalated, there may be a change in   the POC which will need to be communicated to all others involved in   handling the incident. When a change in the POC occurs, old POC   should brief the new POC in all background information.   Lastly, users must know how to report suspected incidents. Sites   should establish reporting procedures that will work both during and   outside normal working hours. Help desks are often used to receive   these reports during normal working hours, while beepers and   telephones can be used for out of hours reporting.5.2.2  Law Enforcement and Investigative Agencies   In the event of an incident that has legal consequences, it is   important to establish contact with investigative agencies (e.g, the   FBI and Secret Service in the U.S.) as soon as possible.  Local law   enforcement, local security offices, and campus police departments   should also be informed as appropriate.   This section describes many   of the issues that will be confronted, but it is acknowledged that   each organization will have its own local and governmental laws and   regulations that will impact how they interact with law enforcement   and investigative agencies. The most important point to make is that   each site needs to work through these issues.   A primary reason for determining these point of contact well in   advance of an incident is that once a major attack is in progress,   there is little time to call these agencies to determine exactly who   the correct point of contact is.  Another reason is that it is   important to cooperate with these agencies in a manner that will   foster a good working relationship, and that will be in accordance   with the working procedures of these agencies.  Knowing the working   procedures in advance, and the expectations of your point of contact   is a big step in this direction.  For example, it is important to   gather evidence that will be admissible in any subsequent legal   proceedings, and this will require prior knowledge of how to gather   such evidence.  A final reason for establishing contacts as soon as   possible is that it is impossible to know the particular agency that   will assume jurisdiction in any given incident.  Making contacts and   finding the proper channels early on will make responding to an   incident go considerably more smoothly.Fraser, Ed.                Informational                       [Page 44]

RFC 2196              Site Security Handbook              September 1997   If your organization or site has a legal counsel, you need to notify   this office soon after you learn that an incident is in progress.  At   a minimum, your legal counsel needs to be involved to protect the   legal and financial interests of your site or organization.  There   are many legal and practical issues, a few of which are:   (1)  Whether your site or organization is willing to risk negative        publicity or exposure to cooperate with legal prosecution        efforts.   (2)  Downstream liability--if you leave a compromised system as is so        it can be monitored and another computer is damaged because the        attack originated from your system, your site or organization        may be liable for damages incurred.   (3)  Distribution of information--if your site or organization        distributes information about an attack in which another site or        organization may be involved or the vulnerability in a product        that may affect ability to market that product, your site or        organization may again be liable for any damages (including        damage of reputation).   (4)  Liabilities due to monitoring--your site or organization may be        sued if users at your site or elsewhere discover that your site        is monitoring account activity without informing users.   Unfortunately, there are no clear precedents yet on the liabilities   or responsibilities of organizations involved in a security incident   or who might be involved in supporting an investigative effort.   Investigators will often encourage organizations to help trace and   monitor intruders.  Indeed, most investigators cannot pursue computer   intrusions without extensive support from the organizations involved.   However, investigators cannot provide protection from liability   claims, and these kinds of efforts may drag out for months and may   take a lot of effort.   On the other hand, an organization's legal council may advise extreme   caution and suggest that tracing activities be halted and an intruder   shut out of the system.  This, in itself, may not provide protection   from liability, and may prevent investigators from identifying the   perpetrator.   The balance between supporting investigative activity and limiting   liability is tricky. You'll need to consider the advice of your legal   counsel and the damage the intruder is causing (if any) when making   your decision about what to do during any particular incident.Fraser, Ed.                Informational                       [Page 45]

RFC 2196              Site Security Handbook              September 1997   Your legal counsel should also be involved in any decision to contact   investigative agencies when an incident occurs at your site.  The   decision to coordinate efforts with investigative agencies is most   properly that of your site or organization.  Involving your legal   counsel will also foster the multi-level coordination between your   site and the particular investigative agency involved, which in turn   results in an efficient division of labor.  Another result is that   you are likely to obtain guidance that will help you avoid future   legal mistakes.   Finally, your legal counsel should evaluate your site's written   procedures for responding to incidents.  It is essential to obtain a   "clean bill of health" from a legal perspective before you actually   carry out these procedures.   It is vital, when dealing with investigative agencies, to verify that   the person who calls asking for information is a legitimate   representative from the agency in question.  Unfortunately, many well   intentioned people have unknowingly leaked sensitive details about   incidents, allowed unauthorized people into their systems, etc.,   because a caller has masqueraded as a representative of a government   agency. (Note: this word of caution actually applies to all external   contacts.)   A similar consideration is using a secure means of communication.   Because many network attackers can easily re-route electronic mail,   avoid using electronic mail to communicate with other agencies (as   well as others dealing with the incident at hand). Non-secured phone   lines (the phones normally used in the business world) are also   frequent targets for tapping by network intruders, so be careful!   There is no one established set of rules for responding to an   incident when the local government becomes involved.  Normally (in   the U.S.), except by legal order, no agency can force you to monitor,   to disconnect from the network, to avoid telephone contact with the   suspected attackers, etc. Each organization will have a set of local   and national laws and regulations that must be adhered to when   handling incidents. It is recommended that each site be familiar with   those laws and regulations, and identify and get know the contacts   for agencies with jurisdiction well in advance of handling an   incident.5.2.3  Computer Security Incident Handling Teams   There are currently a number of of Computer Security Incident   Response teams (CSIRTs) such as the CERT Coordination Center, the   German DFN-CERT, and other teams around the globe.  Teams exist for   many major government agencies and large corporations.  If such aFraser, Ed.                Informational                       [Page 46]

RFC 2196              Site Security Handbook              September 1997   team is available, notifying it should be of primary consideration   during the early stages of an incident.  These teams are responsible   for coordinating computer security incidents over a range of sites   and larger entities.  Even if the incident is believed to be   contained within a single site, it is possible that the information   available through a response team could help in fully resolving the   incident.   If it is determined that the breach occurred due to a flaw in the   system's hardware or software, the vendor (or supplier) and a   Computer Security Incident Handling team should be notified as soon   as possible.  This is especially important because many other systems   are vulnerable, and these vendor and response team organizations can   help disseminate help to other affected sites.   In setting up a site policy for incident handling, it may be   desirable to create a subgroup, much like those teams that already   exist, that will be responsible for handling computer security   incidents for the site (or organization).  If such a team is created,   it is essential that communication lines be opened between this team   and other teams.  Once an incident is under way, it is difficult to   open a trusted dialogue between other teams if none has existed   before.5.2.4  Affected and Involved Sites   If an incident has an impact on other sites, it is good practice to   inform them.  It may be obvious from the beginning that the incident   is not limited to the local site, or it may emerge only after further   analysis.   Each site may choose to contact other sites directly or they can pass   the information to an appropriate incident response team. It is often   very difficult to find the responsible POC at remote sites and the   incident response team will be able to  facilitate contact by making   use of already established channels.   The legal and liability issues arising from a security incident will   differ from site to site.  It is important to define a policy for the   sharing and logging of information about other sites before an   incident occurs.   Information about specific people is especially sensitive, and may be   subject to privacy laws.  To avoid problems in this area, irrelevant   information should be deleted and a statement of how to handle the   remaining information should be included.  A clear statement of how   this information is to be used is essential.  No one who informs a   site of a security incident wants to read about it in the publicFraser, Ed.                Informational                       [Page 47]

RFC 2196              Site Security Handbook              September 1997   press.  Incident response teams are valuable in this respect.  When   they pass information to responsible POCs, they are able to protect   the anonymity of the original source. But, be aware that, in many   cases, the analysis of logs and information at other sites will   reveal addresses of your site.   All the problems discussed above should be not taken as reasons not   to involve other sites.  In fact, the experiences of existing teams   reveal that most sites informed about security problems are not even   aware that their site had been compromised.  Without timely   information, other sites are often unable to take action against   intruders.5.2.5  Internal Communications   It is crucial during a major incident to communicate why certain   actions are being taken, and how the users (or departments) are   expected to behave. In particular, it should be made very clear to   users what they are allowed to say (and not say) to the outside world   (including other departments). For example, it wouldn't be good for   an organization if users replied to customers with something like,   "I'm sorry the systems are down, we've had an intruder and we are   trying to clean things up." It would be much better if they were   instructed to respond with a prepared statement like, "I'm sorry our   systems are unavailable, they are being maintained for better service   in the future."   Communications with customers and contract partners should be handled   in a sensible, but sensitive way. One can prepare for the main issues   by preparing a checklist. When an incident occurs, the checklist can   be used with the addition of a sentence or two for the specific   circumstances of the incident.   Public relations departments can be very helpful during incidents.   They should be involved in all planning and can provide well   constructed responses for use when contact with outside departments   and organizations is necessary.5.2.6  Public Relations - Press Releases   There has been a tremendous growth in the amount of media coverage   dedicated to computer security incidents in the United States. Such   press coverage is bound to extend to other countries as the Internet   continues to grow and expand internationally.  Readers from countries   where such media attention has not yet occurred, can learn from the   experiences in the U.S. and should be forwarned and prepared.Fraser, Ed.                Informational                       [Page 48]

RFC 2196              Site Security Handbook              September 1997   One of the most important issues to consider is when, who, and how   much to release to the general public through the press.  There are   many issues to consider when deciding this particular issue.  First   and foremost, if a public relations office exists for the site, it is   important to use this office as liaison to the press.  The public   relations office is trained in the type and wording of information   released, and will help to assure that the image of the site is   protected during and after the incident (if possible).  A public   relations office has the advantage that you can communicate candidly   with them, and provide a buffer between the constant press attention   and the need of the POC to maintain control over the incident.   If a public relations office is not available, the information   released to the press must be carefully considered.  If the   information is sensitive, it may be advantageous to provide only   minimal or overview information to the press.  It is quite possible   that any information provided to the press will be quickly reviewed   by the perpetrator of the incident.  Also note that misleading the   press can often backfire and cause more damage than releasing   sensitive information.   While it is difficult to determine in advance what level of detail to   provide to the press, some guidelines to keep in mind are:   (1)  Keep the technical level of detail low.  Detailed        information about the incident may provide enough        information for others to launch similar attacks on        other sites, or even damage the site's ability to        prosecute the guilty party once the event is over.   (2)  Keep the speculation out of press statements.        Speculation of who is causing the incident or the        motives are very likely to be in error and may cause        an inflamed view of the incident.   (3)  Work with law enforcement professionals to assure that        evidence is protected.  If prosecution is involved,        assure that the evidence collected is not divulged to        the press.   (4)  Try not to be forced into a press interview before you are        prepared.  The popular press is famous for the "2 am"        interview, where the hope is to catch the interviewee off        guard and obtain information otherwise not available.   (5)  Do not allow the press attention to detract from the        handling of the event.  Always remember that the successful        closure of an incident is of primary importance.Fraser, Ed.                Informational                       [Page 49]

RFC 2196              Site Security Handbook              September 19975.3  Identifying an Incident5.3.1  Is It Real?   This stage involves determining if a problem really exists.  Of   course many if not most signs often associated with virus infection,   system intrusions, malicious users, etc., are simply anomalies such   as hardware failures or suspicious system/user behavior.  To assist   in identifying whether there really is an incident, it is usually   helpful to obtain and use any detection software which may be   available.  Audit information is also extremely useful, especially in   determining whether there is a network attack.  It is extremely   important to obtain a system snapshot as soon as one suspects that   something is wrong.  Many incidents cause a dynamic chain of events   to occur, and an initial system snapshot may be the most valuable   tool for identifying the problem and any source of attack.  Finally,   it is important to start a log book.  Recording system events,   telephone conversations, time stamps, etc., can lead to a more rapid   and systematic identification of the problem, and is the basis for   subsequent stages of incident handling.   There are certain indications or "symptoms" of an incident that   deserve special attention:   (1)   System crashes.   (2)   New user accounts (the account RUMPLESTILTSKIN has been         unexpectedly created), or high activity on a previously         low usage account.   (3)   New files (usually with novel or strange file names,         such as data.xx or k or .xx ).   (4)   Accounting discrepancies (in a UNIX system you might         notice the shrinking of an accounting file called         /usr/admin/lastlog, something that should make you very         suspicious that there may be an intruder).   (5)   Changes in file lengths or dates (a user should be         suspicious if .EXE files in an MS DOS computer have         unexplainedly grown by over 1800 bytes).   (6)   Attempts to write to system (a system manager notices         that a privileged user in a VMS system is attempting to         alter RIGHTSLIST.DAT).   (7)   Data modification or deletion (files start to disappear).   (8)   Denial of service (a system manager and all other users         become locked out of a UNIX system, now in single user mode).   (9)   Unexplained, poor system performance   (10)  Anomalies ("GOTCHA" is displayed on the console or there         are frequent unexplained "beeps").   (11)  Suspicious probes (there are numerous unsuccessful login         attempts from another node).Fraser, Ed.                Informational                       [Page 50]

RFC 2196              Site Security Handbook              September 1997   (12)  Suspicious browsing (someone becomes a root user on a UNIX         system and accesses file after file on many user accounts.)   (13)  Inability of a user to log in due to modifications of his/her         account.   By no means is this list comprehensive; we have just listed a number   of common indicators.  It is best to collaborate with other technical   and computer security personnel to make a decision as a group about   whether an incident is occurring.5.3.2  Types and Scope of Incidents   Along with the identification of the incident is the evaluation of   the scope and impact of the problem.  It is important to correctly   identify the boundaries of the incident in order to effectively deal   with it and prioritize responses.   In order to identify the scope and impact a set of criteria should be   defined which is appropriate to the site and to the type of   connections available.  Some of the issues include:   (1)  Is this a multi-site incident?   (2)  Are many computers at your site affected by this incident?   (3)  Is sensitive information involved?   (4)  What is the entry point of the incident (network,        phone line, local terminal, etc.)?   (5)  Is the press involved?   (6)  What is the potential damage of the incident?   (7)  What is the estimated time to close out the incident?   (8)  What resources could be required to handle the incident?   (9)  Is law enforcement involved?5.3.3  Assessing the Damage and Extent   The analysis of the damage and extent of the incident can be quite   time consuming, but should lead to some insight into the nature of   the incident, and aid investigation and prosecution.  As soon as the   breach has occurred, the entire system and all of its components   should be considered suspect.  System software is the most probable   target.  Preparation is key to be able to detect all changes for a   possibly tainted system.  This includes checksumming all media from   the vendor using a algorithm which is resistant to tampering.  (See   sections4.3)   Assuming original vendor distribution media are available, an   analysis of all system files should commence, and any irregularities   should be noted and referred to all parties involved in handling the   incident.  It can be very difficult, in some cases, to decide whichFraser, Ed.                Informational                       [Page 51]

RFC 2196              Site Security Handbook              September 1997   backup media are showing a correct system status. Consider, for   example, that the incident may have continued for months or years   before discovery, and the suspect may be an employee of the site, or   otherwise have intimate knowledge or access to the systems.  In all   cases, the pre-incident preparation will determine what recovery is   possible.   If the system supports centralized logging (most do), go back over   the logs and look for abnormalities.  If process accounting and   connect time accounting is enabled, look for patterns of system   usage.  To a lesser extent, disk usage may shed light on the   incident.  Accounting can provide much helpful information in an   analysis of an incident and subsequent prosecution.  Your ability to   address all aspects of a specific incident strongly depends on the   success of this analysis.5.4  Handling an Incident   Certain steps are necessary to take during the handling of an   incident.  In all security related activities, the most important   point to be made is that all sites should have policies in place.   Without defined policies and goals, activities undertaken will remain   without focus. The goals should be defined by management and legal   counsel in advance.   One of the most fundamental objectives is to restore control of the   affected systems and to limit the impact and damage.  In the worst   case scenario, shutting down the system, or disconnecting the system   from the network, may the only practical solution.   As the activities involved are complex, try to get as much help as   necessary.  While trying to solve the problem alone, real damage   might occur due to delays or missing information.  Most   administrators take the discovery of an intruder as a personal   challenge.  By proceeding this way, other objectives as outlined in   the local policies may not always be considered.  Trying to catch   intruders may be a very low priority, compared to system integrity,   for example.  Monitoring a hacker's activity is useful, but it might   not be considered worth the risk to allow the continued access.5.4.1  Types of Notification and Exchange of Information   When you have confirmed that an incident is occurring, the   appropriate personnel must be notified.  How this notification is   achieved is very important to keeping the event under control both   from a technical and emotional standpoint. The circumstances should   be described in as much detail as possible, in order to aid prompt   acknowledgment and understanding of the problem.  Great care shouldFraser, Ed.                Informational                       [Page 52]

RFC 2196              Site Security Handbook              September 1997   be taken when determining to which groups detailed technical   information is given during the notification.  For example, it is   helpful to pass this kind of information to an incident handling team   as they can assist you by providing helpful hints for eradicating the   vulnerabilities involved in an incident.  On the other hand, putting   the critical knowledge into the public domain (e.g., via USENET   newsgroups or mailing lists) may potentially put a large number of   systems at risk of intrusion.  It is invalid to assume that all   administrators reading a particular newsgroup have access to   operating system source code, or can even understand an advisory well   enough to take adequate steps.   First of all, any notification to either local or off-site personnel   must be explicit.  This requires that any statement (be it an   electronic mail message, phone call, fax, beeper, or semaphone)   providing information about the incident be clear, concise, and fully   qualified.  When you are notifying others that will help you handle   an event, a "smoke screen" will only divide the effort and create   confusion.  If a division of labor is suggested, it is helpful to   provide information to each participant about what is being   accomplished in other efforts.  This will not only reduce duplication   of effort, but allow people working on parts of the problem to know   where to obtain information relevant to their part of the incident.   Another important consideration when communicating about the incident   is to be factual.  Attempting to hide aspects of the incident by   providing false or incomplete information may not only prevent a   successful resolution to the incident, but may even worsen the   situation.   The choice of language used when notifying people about the incident   can have a profound effect on the way that information is received.   When you use emotional or inflammatory terms, you raise the potential   for damage and negative outcomes of the incident.  It is important to   remain calm both in written and spoken communications.   Another consideration is that not all people speak the same language.   Due to this fact, misunderstandings and delay may arise, especially   if it is a multi-national incident. Other international concerns   include differing legal implications of a security incident and   cultural differences.  However, cultural differences do not only   exist between countries.  They even exist within countries, between   different social or user groups.  For example, an administrator of a   university system might be very relaxed about attempts to connect to   the system via telnet, but the administrator of a military system is   likely to consider the same action as a possible attack.Fraser, Ed.                Informational                       [Page 53]

RFC 2196              Site Security Handbook              September 1997   Another issue associated with the choice of language is the   notification of non-technical or off-site personnel.  It is important   to accurately describe the incident without generating undue alarm or   confusion.  While it is more difficult to describe the incident to a   non-technical audience, it is often more important.  A non-technical   description may be required for upper-level management, the press, or   law enforcement liaisons.  The importance of these communications   cannot be underestimated and may make the difference between   resolving the incident properly and escalating to some higher level   of damage.   If an incident response team becomes involved, it might be necessary   to fill out a template for the information exchange.  Although this   may seem to be an additional burden and adds a certain delay, it   helps the team to act on this minimum set of information.  The   response team may be able to respond to aspects of the incident of   which the local administrator is unaware. If information is given out   to someone else, the following minimum information should be   provided:   (1)  timezone of logs, ... in GMT or local time   (2)  information about the remote system, including host names,        IP addresses and (perhaps) user IDs   (3)  all log entries relevant for the remote site   (4)  type of incident (what happened, why should you care)   If local information (i.e., local user IDs) is included in the log   entries, it will be necessary to sanitize the entries beforehand to   avoid privacy issues.  In general, all information which might assist   a remote site in resolving an incident should be given out, unless   local policies prohibit this.5.4.2  Protecting Evidence and Activity Logs   When you respond to an incident, document all details related to the   incident.  This will provide valuable information to yourself and   others as you try to unravel the course of events.  Documenting all   details will ultimately save you time.  If you don't document every   relevant phone call, for example, you are likely to forget a   significant portion of information you obtain, requiring you to   contact the source of information again.  At the same time, recording   details will provide evidence for prosecution efforts, providing the   case moves in that direction.  Documenting an incident will also help   you perform a final assessment of damage (something your management,   as well as law enforcement officers, will want to know), and will   provide the basis for later phases of the handling process:   eradication, recovery, and follow-up "lessons learned."Fraser, Ed.                Informational                       [Page 54]

RFC 2196              Site Security Handbook              September 1997   During the initial stages of an incident, it is often infeasible to   determine whether prosecution is viable, so you should document as if   you are gathering evidence for a court case.  At a minimum, you   should record:   (1)  all system events (audit records)   (2)  all actions you take (time tagged)   (3)  all external conversations (including the person with whom        you talked, the date and time, and the content of the        conversation)   The most straightforward way to maintain documentation is keeping a   log book.  This allows you to go to a centralized, chronological   source of information when you need it, instead of requiring you to   page through individual sheets of paper.  Much of this information is   potential evidence in a court of law.  Thus, when a legal follow-up   is a possibility, one should follow the prepared procedures and avoid   jeopardizing the legal follow-up by improper handling of possible   evidence. If appropriate, the following steps may be taken.   (1)  Regularly (e.g., every day) turn in photocopied, signed        copies of your logbook (as well as media you use to record        system events) to a document custodian.   (2)  The custodian should store these copied pages in a secure        place (e.g., a safe).   (3)  When you submit information for storage, you should        receive a signed, dated receipt from the document        custodian.   Failure to observe these procedures can result in invalidation of any   evidence you obtain in a court of law.5.4.3  Containment   The purpose of containment is to limit the extent of an attack.  An   essential part of containment is decision making (e.g., determining   whether to shut a system down, disconnect from a network, monitor   system or network activity, set traps, disable functions such as   remote file transfer, etc.).   Sometimes this decision is trivial; shut the system down if the   information is classified, sensitive, or proprietary.  Bear in mind   that removing all access while an incident is in progress obviously   notifies all users, including the alleged problem users, that the   administrators are aware of a problem; this may have a deleteriousFraser, Ed.                Informational                       [Page 55]

RFC 2196              Site Security Handbook              September 1997   effect on an investigation.  In some cases, it is prudent to remove   all access or functionality as soon as possible, then restore normal   operation in limited stages.  In other cases, it is worthwhile to   risk some damage to the system if keeping the system up might enable   you to identify an intruder.   This stage should involve carrying out predetermined procedures.   Your organization or site should, for example, define acceptable   risks in dealing with an incident, and should prescribe specific   actions and strategies accordingly.  This is especially important   when a quick decision is necessary and it is not possible to first   contact all involved parties to discuss the decision.  In the absence   of predefined procedures, the person in charge of the incident will   often not have the power to make difficult management decisions (like   to lose the results of a costly experiment by shutting down a   system).  A final activity that should occur during this stage of   incident handling is the notification of appropriate authorities.5.4.4  Eradication   Once the incident has been contained, it is time to eradicate the   cause.  But before eradicating the cause, great care should be taken   to collect all necessary information about the compromised system(s)   and the cause of the incident as they will likely be lost when   cleaning up the system.   Software may be available to help you in the eradication process,   such as anti-virus software.  If any bogus files have been created,   archive them before deleting them.  In the case of virus infections,   it is important to clean and reformat any media containing infected   files.  Finally, ensure that all backups are clean.  Many systems   infected with viruses become periodically re-infected simply because   people do not systematically eradicate the virus from backups.  After   eradication, a new backup should be taken.   Removing all vulnerabilities once an incident has occurred is   difficult.  The key to removing vulnerabilities is knowledge and   understanding of the breach.   It may be necessary to go back to the original distribution media and   re-customize the system.  To facilitate this worst case scenario, a   record of the original system setup and each customization change   should be maintained.  In the case of a network-based attack, it is   important to install patches for each operating system vulnerability   which was exploited.Fraser, Ed.                Informational                       [Page 56]

RFC 2196              Site Security Handbook              September 1997   As discussed insection 5.4.2, a security log can be most valuable   during this phase of removing vulnerabilities. The logs showing how   the incident was discovered and contained can be used later to help   determine how extensive the damage was from a given incident.  The   steps taken can be used in the future to make sure the problem does   not resurface.  Ideally, one should automate and regularly apply the   same test as was used to detect the security incident.   If a particular vulnerability is isolated as having been exploited,   the next step is to find a mechanism to protect your system.  The   security mailing lists and bulletins would be a good place to search   for this information, and you can get advice from incident response   teams.5.4.5  Recovery   Once the cause of an incident has been eradicated, the recovery phase   defines the next stage of action.  The goal of recovery is to return   the system to normal.  In general, bringing up services in the order   of demand to allow a minimum of user inconvenience is the best   practice.  Understand that the proper recovery procedures for the   system are extremely important and should be specific to the site.5.4.6  Follow-Up   Once you believe that a system has been restored to a "safe" state,   it is still possible that holes, and even traps, could be lurking in   the system.  One of the most important stages of responding to   incidents is also the most often omitted, the follow-up stage.  In   the follow-up stage, the system should be monitored for items that   may have been missed during the cleanup stage.  It would be prudent   to utilize some of the tools mentioned in chapter 7 as a start.   Remember, these tools don't replace continual system monitoring and   good systems administration practices.   The most important element of the follow-up stage is performing a   postmortem analysis.  Exactly what happened, and at what times?  How   well did the staff involved with the incident perform?  What kind of   information did the staff need quickly, and how could they have   gotten that information as soon as possible?  What would the staff do   differently next time?   After an incident, it is prudent to write a report describing the   exact sequence of events: the method of discovery, correction   procedure, monitoring procedure, and a summary of lesson learned.   This will aid in the clear understanding of the problem.  Creating a   formal chronology of events (including time stamps) is also important   for legal reasons.Fraser, Ed.                Informational                       [Page 57]

RFC 2196              Site Security Handbook              September 1997   A follow-up report is valuable for many reasons.  It provides a   reference to be used in case of other similar incidents.  It is also   important to, as quickly as possible obtain a monetary estimate of   the amount of damage the incident caused. This estimate should   include costs associated with any loss of software and files   (especially the value of proprietary data that may have been   disclosed), hardware damage, and manpower costs to restore altered   files, reconfigure affected systems, and so forth.  This estimate may   become the basis for subsequent prosecution activity.  The report can   also help justify an organization's computer security effort to   management.5.5  Aftermath of an Incident   In the wake of an incident, several actions should take place.  These   actions can be summarized as follows:   (1)  An inventory should be taken of the systems' assets,        (i.e., a careful examination should determine how the        system was affected by the incident).   (2)  The lessons learned as a result of the incident        should be included in revised security plan to        prevent the incident from re-occurring.   (3)  A new risk analysis should be developed in light of the        incident.   (4)  An investigation and prosecution of the individuals        who caused the incident should commence, if it is        deemed desirable.   If an incident is based on poor policy, and unless the policy is   changed, then one is doomed to repeat the past.  Once a site has   recovered from and incident, site policy and procedures should be   reviewed to encompass changes to prevent similar incidents.  Even   without an incident, it would be prudent to review policies and   procedures on a regular basis.  Reviews are imperative due to today's   changing computing environments.   The whole purpose of this post mortem process is to improve all   security measures to protect the site against future attacks.  As a   result of an incident, a site or organization should gain practical   knowledge from the experience.  A concrete goal of the post mortem is   to develop new proactive methods.  Another important facet of the   aftermath may be end user and administrator education to prevent a   reoccurrence of the security problem.Fraser, Ed.                Informational                       [Page 58]

RFC 2196              Site Security Handbook              September 19975.6  Responsibilities5.6.1  Not Crossing the Line   It is one thing to protect one's own network, but quite another to   assume that one should protect other networks.  During the handling   of an incident, certain system vulnerabilities of one's own systems   and the systems of others become apparent.  It is quite easy and may   even be tempting to pursue the intruders in order to track them.   Keep in mind that at a certain point it is possible to "cross the   line," and, with the best of intentions, become no better than the   intruder.   The best rule when it comes to propriety is to not use any facility   of remote sites which is not public.  This clearly excludes any entry   onto a system (such as a remote shell or login session) which is not   expressly permitted.  This may be very tempting; after a breach of   security is detected, a system administrator may have the means to   "follow it up," to ascertain what damage is being done to the remote   site.  Don't do it!  Instead, attempt to reach the appropriate point   of contact for the affected site.5.6.2  Good Internet Citizenship   During a security incident there are two choices one can make.   First, a site can choose to watch the intruder in the hopes of   catching him; or, the site can go about cleaning up after the   incident and shut the intruder out of the systems.  This is a   decision that must be made very thoughtfully, as there may be legal   liabilities if you choose to leave your site open, knowing that an   intruder is using your site as a launching pad to reach out to other   sites.  Being a good Internet citizen means that you should try to   alert other sites that may have been impacted by the intruder.  These   affected sites may be readily apparent after a thorough review of   your log files.5.6.3  Administrative Response to Incidents   When a security incident involves a user, the site's security policy   should describe what action is to be taken.  The transgression should   be taken seriously, but it is very important to be sure of the role   the user played.  Was the user naive?  Could there be a mistake in   attributing the security breach to the user?  Applying administrative   action that assumes the user intentionally caused the incident mayFraser, Ed.                Informational                       [Page 59]

RFC 2196              Site Security Handbook              September 1997   not be appropriate for a user who simply made a mistake.  It may be   appropriate to include sanctions more suitable for such a situation   in your policies (e.g., education or reprimand of a user) in addition   to more stern measures for intentional acts of intrusion and system   misuse.6.  Ongoing Activities   At this point in time, your site has hopefully developed a complete   security policy and has developed procedures to assist in the   configuration and management of your technology in support of those   policies.  How nice it would be if you could sit back and relax at   this point and know that you were finished with the job of security.   Unfortunately, that isn't possible.  Your systems and networks are   not a static environment, so you will need to review policies and   procedures on a regular basis.  There are a number of steps you can   take to help you keep up with the changes around you so that you can   initiate corresponding actions to address those changes.  The   following is a starter set and you may add others as appropriate for   your site.   (1)  Subscribe to advisories that are issued by various security incident        response teams, like those of the CERT Coordination Center, and        update your systems against those threats that apply to your site's        technology.   (2)  Monitor security patches that are produced by the vendors of your        equipment, and obtain and install all that apply.   (3)  Actively watch the configurations of your systems to identify any        changes that may have occurred, and investigate all anomalies.   (4)  Review all security policies and procedures annually (at a minimum).   (5)  Read relevant mailing lists and USENET newsgroups to keep up to        date with the latest information being shared by fellow        administrators.   (6)  Regularly check for compliance with policies and procedures.  This        audit should be performed by someone other than the people who        define or implement the policies and procedures.7.  Tools and Locations   This chapter provides a brief list of publicly available security   technology which can be downloaded from the Internet.  Many of the   items described below will undoubtedly be surpassed or made obsolete   before this document is published.Fraser, Ed.                Informational                       [Page 60]

RFC 2196              Site Security Handbook              September 1997   Some of the tools listed are applications such as end user programs   (clients) and their supporting system infrastructure (servers).   Others are tools that a general user will never see or need to use,   but may be used by applications, or by administrators to troubleshoot   security problems or to guard against intruders.   A sad fact is that there are very few security conscious applications   currently available. Primarily, this is caused by the need for a   security infrastructure which must first be put into place for most   applications to operate securely.  There is considerable effort   currently taking place to build this infrastructure so that   applications can take advantage of secure communications.   Most of the tools and applications described below can be found in   one of the following archive sites:   (1)  CERT Coordination Centerftp://info.cert.org:/pub/tools   (2)  DFN-CERTftp://ftp.cert.dfn.de/pub/tools/   (3)  Computer Operations, Audit, and Security Tools (COAST)        coast.cs.purdue.edu:/pub/tools   It is important to note that many sites, including CERT and COAST are   mirrored throughout the Internet.  Be careful to use a "well known"   mirror site to retrieve software, and to use verification tools (md5   checksums, etc.) to validate that software.  A clever cracker might   advertise security software that has intentionally been designed to   provide access to data or systems.Tools   COPS   DES   Drawbridge   identd (not really a security tool)   ISS   Kerberos   logdaemon   lsof   MD5   PEM   PGP   rpcbind/portmapper replacement   SATAN   sfingerd   S/KEY   smrshFraser, Ed.                Informational                       [Page 61]

RFC 2196              Site Security Handbook              September 1997   ssh   swatch   TCP-Wrapper   tiger   Tripwire*   TROJAN.PL8.  Mailing Lists and Other Resources   It would be impossible to list all of the mail-lists and other   resources dealing with site security. However, these are some "jump-   points"  from which the reader can begin. All of these references are   for the "INTERNET" constituency. More specific (vendor and   geographical) resources can be found through these references.   Mailing Lists   (1)  CERT(TM) Advisory        Send mail to:  cert-advisory-request@cert.org        Message Body:  subscribe cert <FIRST NAME> <LAST NAME>        A CERT advisory provides information on how to obtain a patch or        details of a workaround for a known computer security problem.        The CERT Coordination Center works with vendors to produce a        workaround or a patch for a problem, and does not publish        vulnerability information until a workaround or a patch is        available. A CERT advisory may also be a warning to our        constituency about ongoing attacks (e.g.,        "CA-91:18.Active.Internet.tftp.Attacks").        CERT advisories are also published on the USENET newsgroup:                     comp.security.announce        CERT advisory archives are available via anonymous FTP from        info.cert.org in the /pub/cert_advisories directory.   (2)  VIRUS-L List        Send mail to:  listserv%lehiibm1.bitnet@mitvma.mit.edu        Message Body:  subscribe virus-L FIRSTNAME LASTNAME        VIRUS-L is a moderated mailing list with a focus        on computer virus issues.  For more information,        including a copy of the posting guidelines, see        the file "virus-l.README", available by anonymous        FTP from cs.ucr.edu.Fraser, Ed.                Informational                       [Page 62]

RFC 2196              Site Security Handbook              September 1997   (3)  Internet Firewalls        Send mail to:  majordomo@greatcircle.com        Message Body:  subscribe firewalls user@host        The Firewalls mailing list is a discussion forum for        firewall administrators and implementors.   USENET newsgroups   (1)  comp.security.announce        The comp.security.announce newsgroup is moderated        and is used solely for the distribution of CERT        advisories.   (2)  comp.security.misc        The comp.security.misc is a forum for the        discussion of computer security, especially as it        relates to the UNIX(r) Operating System.   (3)  alt.security        The alt.security newsgroup is also a forum for the        discussion of computer security, as well as other        issues such as car locks and alarm systems.   (4)  comp.virus        The comp.virus newsgroup is a moderated newsgroup        with a focus on computer virus issues.  For more        information, including a copy of the posting        guidelines, see the file "virus-l.README",        available via anonymous FTP on info.cert.org        in the /pub/virus-l directory.   (5)  comp.risks        The comp.risks newsgroup is a moderated forum on        the risks to the public in computers and related        systems.   World-Wide Web Pages   (1)http://www.first.org/        Computer Security Resource Clearinghouse. The main focus is on        crisis response information; information on computer        security-related threats, vulnerabilities, and solutions. At the        same time, the Clearinghouse strives to be a general index to        computer security information on a broad variety of subjects,        including general risks, privacy, legal issues, viruses,        assurance, policy, and training.Fraser, Ed.                Informational                       [Page 63]

RFC 2196              Site Security Handbook              September 1997   (2)http://www.telstra.com.au/info/security.html        This Reference Index contains a list of links to information        sources on Network and Computer Security. There is no implied        fitness to the Tools, Techniques and Documents contained within this        archive. Many if not all of these items work well, but we do        not guarantee that this will be so. This information is for the        education and legitimate use of computer security techniques only.   (3)http://www.alw.nih.gov/Security/security.html        This page features general information about computer security.        Information is organized by source and each section is organized        by topic. Recent modifications are noted in What's New page.   (4)http://csrc.ncsl.nist.gov        This archive at the National Institute of Standards and Technology's        Computer Security Resource Clearinghouse page contains a number of        announcements, programs, and documents related to computer security.   * CERT and Tripwire are registered in the U.S. Patent and Trademark Office9.  References   The following references may not be available in all countries.   [Appelman, et. al., 1995] Appelman, Heller, Ehrman, White, and   McAuliffe, "The Law and The Internet", USENIX 1995 Technical   Conference on UNIX and Advanced Computing, New Orleans, LA, January   16-20, 1995.   [ABA, 1989] American Bar Association, Section of Science and   Technology, "Guide to the Prosecution of Telecommunication Fraud by   the Use of Computer Crime Statutes", American Bar Association, 1989.   [Aucoin, 1989] R. Aucoin, "Computer Viruses: Checklist for Recovery",   Computers in  Libraries, Vol. 9, No. 2, Pg. 4, February 1989.   [Barrett, 1996] D. Barrett, "Bandits on the Information   Superhighway", O'Reilly & Associates, Sebastopol, CA, 1996.   [Bates, 1992] R. Bates, "Disaster Recovery Planning: Networks,   Telecommunications and Data Communications", McGraw-Hill, 1992.   [Bellovin, 1989] S. Bellovin, "Security Problems in the TCP/IP   Protocol Suite", Computer Communication Review, Vol 19, 2, pp. 32-48,   April 1989.Fraser, Ed.                Informational                       [Page 64]

RFC 2196              Site Security Handbook              September 1997   [Bellovin, 1990] S. Bellovin, and M. Merritt, "Limitations of the   Kerberos Authentication System", Computer Communications Review,   October 1990.   [Bellovin, 1992] S. Bellovin, "There Be Dragon", USENIX: Proceedings   of the Third Usenix Security Symposium, Baltimore, MD. September,   1992.   [Bender, 1894] D. Bender, "Computer Law: Evidence and Procedure", M.   Bender, New York, NY, 1978-present.   [Bloombecker, 1990] B. Bloombecker, "Spectacular Computer Crimes",   Dow Jones- Irwin, Homewood, IL. 1990.   [Brand, 1990] R. Brand, "Coping with the Threat of Computer Security   Incidents: A Primer from Prevention through Recovery", R. Brand, 8   June 1990.   [Brock, 1989] J. Brock, "November 1988 Internet Computer Virus and   the Vulnerability of National Telecommunications Networks to Computer   Viruses", GAO/T-IMTEC-89-10, Washington, DC, 20 July 1989.   [BS 7799] British Standard, BS Tech Cttee BSFD/12, Info. Sec. Mgmt,   "BS 7799 : 1995 Code of Practice for Information Security   Management", British Standards Institution, London, 54, Effective 15   February 1995.   [Caelli, 1988] W. Caelli, Editor, "Computer Security in the Age of   Information", Proceedings of the Fifth IFIP International Conference   on Computer Security, IFIP/Sec '88.   [Carroll, 1987] J. Carroll, "Computer Security", 2nd Edition,   Butterworth Publishers, Stoneham, MA, 1987.   [Cavazos and Morin, 1995] E. Cavazos and G. Morin, "Cyber-Space and   The Law", MIT Press, Cambridge, MA, 1995.   [CCH, 1989] Commerce Clearing House, "Guide to Computer Law",   (Topical Law Reports), Chicago, IL., 1989.   [Chapman, 1992] B. Chapman, "Network(In) Security Through IP Packet   Filtering", USENIX: Proceedings of the Third UNIX Security Symposium,   Baltimore, MD, September 1992.   [Chapman and Zwicky, 1995] B. Chapman and E. Zwicky, "Building   Internet Firewalls", O'Reilly and Associates, Sebastopol, CA, 1995.Fraser, Ed.                Informational                       [Page 65]

RFC 2196              Site Security Handbook              September 1997   [Cheswick, 1990] B. Cheswick, "The Design of a Secure Internet   Gateway", Proceedings of the Summer Usenix Conference, Anaheim, CA,   June 1990.   [Cheswick1] W. Cheswick, "An Evening with Berferd In Which a Cracker   is Lured, Endured, and Studied", AT&T Bell Laboratories.   [Cheswick and Bellovin, 1994] W. Cheswick and S. Bellovin, "Firewalls   and Internet Security: Repelling the Wily Hacker", Addison-Wesley,   Reading, MA, 1994.   [Conly, 1989] C. Conly, "Organizing for Computer Crime Investigation   and Prosecution", U.S. Dept. of Justice, Office of Justice Programs,   Under Contract  Number OJP-86-C-002, National Institute of Justice,   Washington, DC, July 1989.   [Cooper, 1989] J. Cooper, "Computer and Communications Security:   Strategies for the 1990s", McGraw-Hill, 1989.   [CPSR, 1989] Computer Professionals for Social Responsibility, "CPSR   Statement on the Computer Virus", CPSR, Communications of the ACM,   Vol. 32, No. 6, Pg. 699, June 1989.   [CSC-STD-002-85, 1985] Department of Defense, "Password Management   Guideline", CSC-STD-002-85, 12 April 1985, 31 pages.   [Curry, 1990] D. Curry, "Improving the Security of Your UNIX System",   SRI International Report ITSTD-721-FR-90-21, April 1990.   [Curry, 1992] D. Curry, "UNIX System Security: A Guide for Users and   Systems Administrators", Addision-Wesley, Reading, MA, 1992.   [DDN88] Defense Data Network, "BSD 4.2 and 4.3 Software Problem   Resolution", DDN MGT Bulletin #43, DDN Network Information Center, 3   November 1988.   [DDN89] DCA DDN Defense Communications System, "DDN Security Bulletin   03", DDN Security Coordination Center, 17 October 1989.   [Denning, 1990] P. Denning, Editor, "Computers Under Attack:   Intruders, Worms, and Viruses", ACM Press, 1990.   [Eichin and Rochlis, 1989] M. Eichin, and J. Rochlis, "With   Microscope and Tweezers: An Analysis of the Internet Virus of   November 1988", Massachusetts Institute of Technology, February 1989.Fraser, Ed.                Informational                       [Page 66]

RFC 2196              Site Security Handbook              September 1997   [Eisenberg, et. al., 89] T. Eisenberg, D. Gries, J. Hartmanis, D.   Holcomb, M. Lynn, and T. Santoro, "The Computer Worm", Cornell   University, 6 February 1989.   [Ermann, Willians, and Gutierrez, 1990] D. Ermann, M. Williams, and   C. Gutierrez, Editors, "Computers, Ethics, and Society", Oxford   University Press, NY, 1990.  (376 pages, includes bibliographical   references).   [Farmer and Spafford, 1990] D. Farmer and E. Spafford, "The COPS   Security Checker System", Proceedings of the Summer 1990 USENIX   Conference, Anaheim, CA, Pgs. 165-170, June 1990.   [Farrow, 1991] Rik Farrow, "UNIX Systems Security", Addison-Wesley,   Reading, MA, 1991.   [Fenwick, 1985] W. Fenwick, Chair, "Computer Litigation, 1985: Trial   Tactics and Techniques", Litigation Course Handbook Series No. 280,   Prepared for distribution at the Computer Litigation, 1985: Trial   Tactics and Techniques Program, February-March 1985.   [Fites 1989] M. Fites, P. Kratz, and A. Brebner, "Control and   Security of Computer Information Systems", Computer Science Press,   1989.   [Fites, Johnson, and Kratz, 1992] Fites, Johnson, and Kratz, "The   Computer Virus Crisis", Van Hostrand Reinhold, 2nd edition, 1992.   [Forester and Morrison, 1990] T. Forester, and P. Morrison, "Computer   Ethics: Tales and Ethical Dilemmas in Computing", MIT Press,   Cambridge, MA, 1990.   [Foster and Morrision, 1990] T. Forester, and P. Morrison, "Computer   Ethics: Tales and Ethical Dilemmas in Computing", MIT Press,   Cambridge, MA, 1990.  (192 pages including index.)   [GAO/IMTEX-89-57, 1989] U.S. General Accounting Office, "Computer   Security - Virus Highlights Need for Improved Internet Management",   United States General Accounting Office, Washington, DC, 1989.   [Garfinkel and Spafford, 1991] S. Garfinkel, and E. Spafford,   "Practical Unix Security", O'Reilly & Associates, ISBN 0-937175-72-2,   May 1991.   [Garfinkel, 1995] S. Garfinkel, "PGP:Pretty Good Privacy", O'Reilly &   Associates, Sebastopol, CA, 1996.Fraser, Ed.                Informational                       [Page 67]

RFC 2196              Site Security Handbook              September 1997   [Garfinkel and Spafford, 1996] S. Garfinkel and E. Spafford,   "Practical UNIX and Internet Security", O'Reilly & Associates,   Sebastopol, CA, 1996.   [Gemignani, 1989] M. Gemignani, "Viruses and Criminal Law",   Communications of the ACM, Vol. 32, No. 6, Pgs. 669-671, June 1989.   [Goodell, 1996] J. Goodell, "The Cyberthief and the Samurai: The True   Story of Kevin Mitnick-And The Man Who Hunted Him Down", Dell   Publishing, 1996.   [Gould, 1989] C. Gould, Editor, "The Information Web: Ethical and   Social Implications of Computer Networking", Westview Press, Boulder,   CO, 1989.   [Greenia, 1989] M. Greenia, "Computer Security Information   Sourcebook", Lexikon Services, Sacramento, CA, 1989.   [Hafner and Markoff, 1991] K. Hafner and J. Markoff, "Cyberpunk:   Outlaws and Hackers on the Computer Frontier", Touchstone, Simon &   Schuster, 1991.   [Hess, Safford, and Pooch] D. Hess, D. Safford, and U. Pooch, "A Unix   Network Protocol Security Study: Network Information Service", Texas   A&M University.   [Hoffman, 1990] L. Hoffman, "Rogue Programs: Viruses, Worms, and   Trojan Horses", Van Nostrand Reinhold, NY, 1990.  (384 pages,   includes bibliographical references and index.)   [Howard, 1995] G. Howard, "Introduction to Internet Security: From   Basics to Beyond", Prima Publishing, Rocklin, CA, 1995.   [Huband and Shelton, 1986] F. Huband, and R. Shelton, Editors,   "Protection of Computer Systems and Software: New Approaches for   Combating Theft of Software and Unauthorized Intrusion", Papers   presented at a workshop sponsored by the National Science Foundation,   1986.   [Hughes, 1995] L. Hughes Jr., "Actually Useful Internet Security   Techniques", New Riders Publishing, Indianapolis, IN, 1995.   [IAB-RFC1087, 1989] Internet Activities Board, "Ethics and the   Internet",RFC 1087, IAB, January 1989.  Also appears in the   Communications of the ACM, Vol. 32, No. 6, Pg. 710, June 1989.Fraser, Ed.                Informational                       [Page 68]

RFC 2196              Site Security Handbook              September 1997   [Icove, Seger, and VonStorch, 1995] D. Icove, K. Seger, and W.   VonStorch, "Computer Crime: A Crimefighter's Handbook", O'Reilly &   Associates, Sebastopol, CA, 1995.   [IVPC, 1996] IVPC, "International Virus Prevention Conference '96   Proceedings", NCSA, 1996.   [Johnson and Podesta] D. Johnson, and J. Podesta, "Formulating A   Company Policy on Access to and Use and Disclosure of Electronic Mail   on Company Computer Systems".   [Kane, 1994] P. Kane, "PC Security and Virus Protection Handbook: The   Ongoing War Against Information Sabotage", M&T Books, 1994.   [Kaufman, Perlman, and Speciner, 1995] C. Kaufman, R. Perlman, and M.   Speciner, "Network Security: PRIVATE Communication in a PUBLIC   World", Prentice Hall, Englewood Cliffs, NJ, 1995.   [Kent, 1990] S. Kent, "E-Mail Privacy for the Internet: New Software   and Strict Registration Procedures will be Implemented this Year",   Business Communications Review, Vol. 20, No. 1, Pg. 55, 1 January   1990.   [Levy, 1984] S. Levy, "Hacker: Heroes of the Computer Revolution",   Delta, 1984.   [Lewis, 1996] S. Lewis, "Disaster Recovery Yellow Pages", The Systems   Audit Group, 1996.   [Littleman, 1996] J. Littleman, "The Fugitive Game: Online with Kevin   Mitnick", Little, Brown, Boston, MA., 1996.   [Lu and Sundareshan, 1989] W. Lu and M. Sundareshan, "Secure   Communication in Internet Environments: A Hierarchical Key Management   Scheme for End-to-End Encryption", IEEE Transactions on   Communications, Vol. 37, No. 10, Pg. 1014, 1 October 1989.   [Lu and Sundareshan, 1990] W. Lu and M. Sundareshan, "A Model for   Multilevel Security in Computer Networks", IEEE Transactions on   Software Engineering, Vol. 16, No. 6, Page 647, 1 June 1990.   [Martin and Schinzinger, 1989] M. Martin, and R. Schinzinger, "Ethics   in Engineering", McGraw Hill, 2nd Edition, 1989.   [Merkle] R. Merkle, "A Fast Software One Way Hash Function", Journal   of Cryptology, Vol. 3, No. 1.Fraser, Ed.                Informational                       [Page 69]

RFC 2196              Site Security Handbook              September 1997   [McEwen, 1989] J. McEwen, "Dedicated Computer Crime Units", Report   Contributors: D. Fester and H. Nugent, Prepared for the National   Institute of Justice, U.S. Department of Justice, by Institute for   Law and Justice, Inc., under contract number OJP-85-C-006,   Washington, DC, 1989.   [MIT, 1989] Massachusetts Institute of Technology, "Teaching Students   About Responsible Use of Computers", MIT, 1985-1986.  Also reprinted   in the Communications of the ACM, Vol. 32, No. 6, Pg. 704, Athena   Project, MIT, June 1989.   [Mogel, 1989] Mogul, J., "Simple and Flexible Datagram Access   Controls for UNIX-based Gateways", Digital Western Research   Laboratory Research Report 89/4, March 1989.   [Muffett, 1992] A. Muffett, "Crack Version 4.1: A Sensible Password   Checker for Unix"   [NCSA1, 1995] NCSA, "NCSA Firewall Policy Guide", 1995.   [NCSA2, 1995] NCSA, "NCSA's Corporate Computer Virus Prevention   Policy Model", NCSA, 1995.   [NCSA, 1996] NCSA, "Firewalls & Internet Security Conference '96   Proceedings", 1996.   [NCSC-89-660-P, 1990] National Computer Security Center, "Guidelines   for Formal Verification Systems", Shipping list no.: 89-660-P, The   Center, Fort George G. Meade, MD, 1 April 1990.   [NCSC-89-254-P, 1988] National Computer Security Center, "Glossary of   Computer Security Terms", Shipping list no.: 89-254-P, The Center,   Fort George G. Meade, MD, 21 October 1988.   [NCSC-C1-001-89, 1989] Tinto, M., "Computer Viruses: Prevention,   Detection, and Treatment", National Computer Security Center C1   Technical Report C1-001-89, June 1989.   [NCSC Conference, 1989] National Computer Security Conference, "12th   National Computer Security Conference: Baltimore Convention Center,   Baltimore, MD, 10-13 October, 1989: Information Systems Security,   Solutions for Today - Concepts for Tomorrow", National Institute of   Standards and National Computer Security Center, 1989.   [NCSC-CSC-STD-003-85, 1985] National Computer Security Center,   "Guidance for Applying the Department of Defense Trusted Computer   System Evaluation Criteria in Specific Environments", CSC-STD-003-85,   NCSC, 25 June 1985.Fraser, Ed.                Informational                       [Page 70]

RFC 2196              Site Security Handbook              September 1997   [NCSC-STD-004-85, 1985] National Computer Security Center, "Technical   Rationale Behind CSC-STD-003-85: Computer Security Requirements",   CSC-STD-004-85, NCSC, 25 June 1985.   [NCSC-STD-005-85, 1985] National Computer Security Center, "Magnetic   Remanence Security Guideline", CSC-STD-005-85, NCSC, 15 November   1985.   [NCSC-TCSEC, 1985] National Computer Security Center, "Trusted   Computer System Evaluation Criteria", DoD 5200.28-STD, CSC-STD-001-   83, NCSC, December 1985.   [NCSC-TG-003, 1987] NCSC, "A Guide to Understanding DISCRETIONARY   ACCESS CONTROL in Trusted Systems", NCSC-TG-003, Version-1, 30   September 1987, 29 pages.   [NCSC-TG-001, 1988] NCSC, "A Guide to Understanding AUDIT in Trusted   Systems", NCSC-TG-001, Version-2, 1 June 1988, 25 pages.   [NCSC-TG-004, 1988] National Computer Security Center, "Glossary of   Computer Security Terms", NCSC-TG-004, NCSC, 21 October 1988.   [NCSC-TG-005, 1987] National Computer Security Center, "Trusted   Network Interpretation", NCSC-TG-005, NCSC, 31 July 1987.   [NCSC-TG-006, 1988] NCSC, "A Guide to Understanding CONFIGURATION   MANAGEMENT in Trusted Systems", NCSC-TG-006, Version-1, 28 March   1988, 31 pages.   [NCSC-TRUSIX, 1990] National Computer Security Center, "Trusted UNIX   Working Group (TRUSIX) rationale for selecting access control list   features for the UNIX system", Shipping list no.: 90-076-P, The   Center, Fort George G. Meade, MD, 1990.   [NRC, 1991] National Research Council, "Computers at Risk: Safe   Computing in the Information Age", National Academy Press, 1991.   [Nemeth, et. al, 1995] E. Nemeth, G. Snyder, S. Seebass, and T. Hein,   "UNIX Systems Administration Handbook", Prentice Hall PTR, Englewood   Cliffs, NJ, 2nd ed. 1995.   [NIST, 1989] National Institute of Standards and Technology,   "Computer Viruses and Related Threats: A Management Guide", NIST   Special Publication 500-166, August 1989.   [NSA] National Security Agency, "Information Systems Security   Products and Services Catalog", NSA, Quarterly Publication.Fraser, Ed.                Informational                       [Page 71]

RFC 2196              Site Security Handbook              September 1997   [NSF, 1988] National Science Foundation, "NSF Poses Code of   Networking Ethics", Communications of the ACM, Vol. 32, No. 6, Pg.   688, June 1989.  Also appears in the minutes of the regular meeting   of the Division Advisory Panel for Networking and Communications   Research and Infrastructure, Dave Farber, Chair, November 29-30,   1988.   [NTISSAM, 1987] NTISS, "Advisory Memorandum on Office Automation   Security Guideline", NTISSAM COMPUSEC/1-87, 16 January 1987, 58   pages.   [OTA-CIT-310, 1987] United States Congress, Office of Technology   Assessment, "Defending Secrets, Sharing Data: New Locks and Keys for   Electronic Information", OTA-CIT-310, October 1987.   [OTA-TCT-606] Congress of the United States, Office of Technology   Assessment, "Information Security and Privacy in Network   Environments", OTA-TCT-606, September 1994.   [Palmer and Potter, 1989] I. Palmer, and G. Potter, "Computer   Security Risk Management", Van Nostrand Reinhold, NY, 1989.   [Parker, 1989] D. Parker, "Computer Crime: Criminal Justice Resource   Manual", U.S. Dept. of Justice, National Institute of Justice, Office   of Justice Programs, Under Contract Number OJP-86-C-002, Washington,   D.C., August 1989.   [Parker, Swope, and Baker, 1990] D. Parker, S. Swope, and B. Baker,   "Ethical Conflicts: Information and Computer Science, Technology and   Business", QED Information Sciences, Inc., Wellesley, MA. (245   pages).   [Pfleeger, 1989] C. Pfleeger, "Security in Computing", Prentice-Hall,   Englewood Cliffs, NJ, 1989.   [Quarterman, 1990] J. Quarterman, J., "The Matrix: Computer Networks   and Conferencing Systems Worldwide", Digital Press, Bedford, MA,   1990.   [Ranum1, 1992] M. Ranum, "An Internet Firewall", Proceedings of World   Conference on Systems Management and Security, 1992.   [Ranum2, 1992] M. Ranum, "A Network Firewall", Digital Equipment   Corporation Washington Open Systems Resource Center, June 12, 1992.   [Ranum, 1993] M. Ranum, "Thinking About Firewalls", 1993.Fraser, Ed.                Informational                       [Page 72]

RFC 2196              Site Security Handbook              September 1997   [Ranum and Avolio, 1994] M. Ranum and F. Avolio, "A Toolkit and   Methods for Internet Firewalls", Trustest Information Systems, 1994.   [Reinhardt, 1992] R. Reinhardt, "An Architectural Overview of UNIX   Network Security"   [Reinhardt, 1993] R. Reinhardt, "An Architectural Overview of UNIX   Network Security", ARINC Research Corporation, February 18, 1993.   [Reynolds-RFC1135, 1989] The Helminthiasis of the Internet,RFC 1135,   USC/Information Sciences Institute, Marina del Rey, CA, December   1989.   [Russell and Gangemi, 1991] D. Russell and G. Gangemi, "Computer   Security Basics" O'Reilly & Associates, Sebastopol, CA, 1991.   [Schneier 1996] B. Schneier, "Applied Cryptography: Protocols,   Algorithms, and Source Code in C", John Wiley & Sons, New York,   second edition, 1996.   [Seeley, 1989] D. Seeley, "A Tour of the Worm", Proceedings of 1989   Winter USENIX Conference, Usenix Association, San Diego, CA, February   1989.   [Shaw, 1986] E. Shaw Jr., "Computer Fraud and Abuse Act of 1986",   Congressional Record (3 June 1986), Washington, D.C., 3 June 1986.   [Shimomura, 1996] T. Shimomura with J. Markoff, "Takedown:The Pursuit   and Capture of Kevin Mitnick, America's Most Wanted Computer Outlaw-   by the Man Who Did It", Hyperion, 1996.   [Shirey, 1990] R. Shirey, "Defense Data Network Security   Architecture", Computer Communication Review, Vol. 20, No. 2, Page   66, 1 April 1990.   [Slatalla and Quittner, 1995] M. Slatalla and J. Quittner, "Masters   of Deception: The Gang that Ruled Cyberspace", Harper Collins   Publishers, 1995.   [Smith, 1989] M. Smith, "Commonsense Computer Security: Your   Practical Guide to Preventing Accidental and Deliberate Electronic   Data Loss", McGraw-Hill, New York, NY, 1989.   [Smith, 1995] D. Smith, "Forming an Incident Response Team", Sixth   Annual Computer Security Incident Handling Workshop, Boston, MA, July   25-29, 1995.Fraser, Ed.                Informational                       [Page 73]

RFC 2196              Site Security Handbook              September 1997   [Spafford, 1988] E. Spafford, "The Internet Worm Program: An   Analysis", Computer Communication Review, Vol. 19, No. 1, ACM SIGCOM,   January 1989.  Also issued as Purdue CS Technical Report CSD-TR-823,   28 November 1988.   [Spafford, 1989] G. Spafford, "An Analysis of the Internet Worm",   Proceedings of the European Software Engineering Conference 1989,   Warwick England, September 1989.  Proceedings published by Springer-   Verlag as: Lecture Notes in Computer Science #387.  Also issued as   Purdue Technical Report #CSD-TR-933.   [Spafford, Keaphy, and Ferbrache, 1989] E. Spafford, K. Heaphy, and   D. Ferbrache, "Computer Viruses: Dealing with Electronic Vandalism   and Programmed Threats", ADAPSO, 1989. (109 pages.)   [Stallings1, 1995] W. Stallings, "Internet Security Handbook", IDG   Books, Foster City CA, 1995.   [Stallings2, 1995] W. Stallings, "Network and InterNetwork Security",   Prentice Hall, , 1995.   [Stallings3, 1995] W. Stallings, "Protect Your Privacy: A Guide for   PGP Users"  PTR Prentice Hall, 1995.   [Stoll, 1988] C. Stoll, "Stalking the Wily Hacker", Communications of   the ACM, Vol. 31, No. 5, Pgs. 484-497, ACM, New York, NY, May 1988.   [Stoll, 1989] C. Stoll, "The Cuckoo's Egg", ISBN 00385-24946-2,   Doubleday, 1989.   [Treese and Wolman, 1993] G. Treese and A. Wolman, "X Through the   Firewall, and Other Applications Relays", Digital Equipment   Corporation, Cambridge Research Laboratory, CRL 93/10, May 3, 1993.   [Trible, 1986] P. Trible, "The Computer Fraud and Abuse Act of 1986",   U.S. Senate Committee on the Judiciary, 1986.   [Venema] W. Venema, "TCP WRAPPER: Network monitoring, access control,   and booby traps", Mathematics and Computing Science, Eindhoven   University of Technology, The Netherlands.   [USENIX, 1988] USENIX, "USENIX Proceedings: UNIX Security Workshop",   Portland, OR, August 29-30, 1988.   [USENIX, 1990] USENIX, "USENIX Proceedings: UNIX Security II   Workshop", Portland, OR, August 27-28, 1990.Fraser, Ed.                Informational                       [Page 74]

RFC 2196              Site Security Handbook              September 1997   [USENIX, 1992] USENIX, "USENIX Symposium Proceedings: UNIX Security   III", Baltimore, MD, September 14-16, 1992.   [USENIX, 1993] USENIX, "USENIX Symposium Proceedings: UNIX Security   IV", Santa Clara, CA, October 4-6, 1993.   [USENIX, 1995] USENIX, "The Fifth USENIX UNIX Security Symposium",   Salt Lake City, UT, June 5-7, 1995.   [Wood, et.al., 1987] C. Wood, W. Banks, S. Guarro, A. Garcia, V.   Hampel, and H. Sartorio, "Computer Security:  A Comprehensive   Controls Checklist", John Wiley and Sons, Interscience Publication,   1987.   [Wrobel, 1993] L. Wrobel, "Writing Disaster Recovery Plans for   Telecommunications Networks and LANS", Artech House, 1993.   [Vallabhaneni, 1989] S. Vallabhaneni, "Auditing Computer Security: A   Manual with Case Studies", Wiley, New York, NY, 1989.Security Considerations   This entire document discusses security issues.Editor Information   Barbara Y. Fraser   Software Engineering Institute   Carnegie Mellon University   5000 Forbes Avenue   Pittsburgh, PA 15213   Phone: (412) 268-5010   Fax:   (412) 268-6989   EMail: byf@cert.orgFraser, Ed.                Informational                       [Page 75]