Movatterモバイル変換

Network Working Group                                           A. GwinnRequest for Comments: 2179                     Networld+Interop NOC TeamCategory: Informational                                        July 1997Network Security For Trade ShowsStatus of this Memo   This memo provides information for the Internet community.  This memo   does not specify an Internet standard of any kind.  Distribution of   this memo is unlimited.Abstract   This document is designed to assist vendors and other participants in   trade shows, such as Networld+Interop, in designing effective   protection against network and system attacks by unauthorized   individuals.  Generally, it has been observed that many system   administrators and trade show coordinators tend to overlook the   importance of system security at trade shows. In fact, systems at   trade shows are at least as prone to attack as office-based   platforms. Trade show systems should be treated as seriously as an   office computer. A breach of security of a trade show system can   render -- and has rendered -- an exhibitor's demonstrations   inoperable -- sometimes for the entire event!   This document is not intended to replace the multitudes of   comprehensive books on the subject of Internet security.  Rather, its   purpose is to provide a checklist-style collection of frequently   overlooked, simple ways to minimize the chance of a costly attack.   We encourage exhibitors to pay special attention to this document and   share it with all associated representatives.Physical Security   Before addressing technical security issues, one of the most   frequently underrated and overlooked security breaches is the simple   low-tech attack.  The common victim is the one who leaves a console   logged in, perhaps as root, and leaves the system.  Other times, an   anonymous "helpful soul" might ask for a password in order to assist   the user in "identifying a problem."  This type of method allows an   intruder, especially one logged in as "root", access to system files.Gwinn                        Informational                      [Page 1]

RFC 2179            Network Security For Trade Shows           July 1997   Tips:   * Educate sales and support staff regarding system logins, especially     "root" or other privileged accounts.   * Identify individuals who are not using exhibit systems for their     intended purpose, especially non-booth personnel.   * Request identification from anyone wishing to access systems     for maintenance purposes unless their identities are known.System Security   This section discusses technical security procedures for workstations   on the vendor network.  Although specifics tend to be for Unix   systems, general procedures apply to all platforms.Password Security   Lack of passwords or easy to guess passwords are a relatively low-   tech door into systems, but are responsible for a significant number   of breakins. Good passwords are a cornerstone of system security.   By default, PC operating systems like Windows 95 and MacOS do not   provide adequate password security. The Windows login password   provides no security (hitting the "ESC" key allows the user to bypass   password entry). Password security for these machines is possible,   but is beyond the scope of this document.   Tips:   * Check /etc/passwd on Unix systems and the user administration     application on other systems for lack of passwords. Some vendors     ship systems with null passwords, in some cases even for     privileged accounts.   * Change passwords, especially system and root passwords.   * Mix case, numbers and punctuation, especially on privileged     accounts.   * Change system passwords on a regular basis.   * Do not use passwords relating to the event, the company, or     products being displayed.  Systems personnel at Networld+Interop,     when asked to assist booth personnel, often guess even root     passwords!Gwinn                        Informational                      [Page 2]

RFC 2179            Network Security For Trade Shows           July 1997Extra Privileged Accounts   Some system vendors have been known to ship systems with multiple   privileged accounts (for example, Unix systems with accounts that   have root privileges [UID=0]). Some vendors may include a separate   system administration account that places a user in a specific   administrative program. Each additional privileged account presents   yet another opportunity for abuse.   Generally, if a Unix system does not need additional root accounts,   these can be disabled by placing "*" in the password field of   /etc/passwd, or by using the administrative tool when a system   employees enhanced security. Verify all systems for extra privileged   accounts and either disable them or change their password as   appropriate.   Make certain that privileged accounts are inaccessible from anywhere   other than the system console.  Frequently systems rely on files such   as /etc/securettys for a list of "secure" terminals.  As a general   rule, unless a terminal is in this file, a root login is not   possible.  Specific use of this feature should be covered in the   system's documentation files.   Tips:   * Check /etc/passwd on Unix systems and the user administration     application on other systems for additional privileged accounts.   * Disable remote login for privileged accounts.   * Disable any unnecessary privileged accounts.   * Limit logins from root accounts to "secure" terminals or the     system console.Use of Authentication Tokens   Authentication tokens such as SecureID, Cryptocard, DES Gold and   others, provide a method of producing "one-time" passwords.  The   principle advantage in a trade-show environment is to render   worthless, packets captured by sniffers on the network.  It should be   treated as fact, that there are many packet sniffers and other   administration tools constantly (legitimately) watching the network-   -especially at a large network-oriented trade show. Typed passwords,   by default, are sent clear text across the network, allowing others   to view them. Authentication tokens provide a password that is only   valid for that one instance, and are useless after that.  A logical   extension of the use of authentication tokens would be to use them   for "trips home" (from the show network to a home site) to minimize   the chance of off-site security problems.Gwinn                        Informational                      [Page 3]

RFC 2179            Network Security For Trade Shows           July 1997   An alternative to these tokens is the secure shell ("ssh") protocol   which provides an encrypted connection between clients and servers.   This connection can carry both login traffic and arbitrary port-to-   port communication, and is a powerful tool for securing an in-booth   network and communications to and from remote systems.   Tips:   * Contact vendors of authentication tokens/cards for further     information as to how to integrate into specific environments, or     on to specific platforms.   * The public-domain utility "cryptosu" (csu), when used with a     Cryptocard, provides a replacement for Unix's "su" command,     employing a challenge/response style of authentication for root     access.   * Explore the use of ssh clients and servers.Anonymous FTP   Anonymous FTP accounts can easily turn into a security hole.  Disable   this service if not specifically needed.  In the event that anonymous   FTP is to be used, the following tips may help secure it.   * When a user logs in as "anonymous", they should be locked into a     specific directory tree. Be sure that FTPd properly chroots to the     appropriate directory. A "cd /" should put an anonymous user at the     top of the "public" tree, and not the system's root directory.   * Some systems may allow symbolic links (or "shortcuts") to take a     user outside the allowed tree. Verify all links inside the     anonymous FTP hierarchy.   * Make sure that ftp's root directory is "owned" by someone other     than the 'ftp' account. Typically, it should be owned by "root".   * Do not use a world-writable incoming directory unless absolutely     necessary. Many sites use these as a way for users to transfer     files into the site. This can, and frequently does, turn into an     archive for stolen software (referred to by the pirate community as     "warez").   * Removing read permissions from the directory permissions (chmod 733     on Unix systems) prohibits an anonymous user from being able to     list the contents of a directory. Files can be deposited as usual,     but not retrieved unless the user knows the exact name of the file.Network File Sharing   Writable file shares without some form of security are invitations to   destruction of information and demonstrations. Whether using NFS on   Unix systems, or PC sharing facilities like CIFS, AppleShare, or   NetWare, close attention should be paid to security of the filesGwinn                        Informational                      [Page 4]

RFC 2179            Network Security For Trade Shows           July 1997   exported.  Keep in mind that one's competition frequently shares the   same network at a trade show!  Security for both read and write   access should be employed and each access point examined.   Exporting a writable NFS filesystem to the world grants anyone the   ability to read and write any file in the exported mount point. If   this is done, for example, with a system directory such as "/" or   "/etc", it is a simple matter to edit password files to create one-   self access to a system. Therefore, /etc/exports should be closely   examined to be certain that nothing of a sensitive nature is exported   to anyone but another trusted host. Anything exported to the general   public should be exported "read-only", and verified for the   information that is available via the file shares.   Tips:   * Do not provide file sharing space unless needed.   * Verify where exported information will be "visible".   * Do not maintain any writable shares unless absolutely necessary!Trusted Hosts   Trusted host entries are a method for allowing other hosts   "equivalent" security access to another host computer. Some vendors   ship systems with open trusted host files.  Make certain that this   issue is addressed.   Tips:   * On Unix systems, check for a '+' entry (all systems trusted) in     /etc/hosts.equiv and all ".rhosts" files (there may be multiple     .rhosts files) and remove it.   * Check for an "xhost +" entry in the "...X11/xdm/Xsession" file.     Most often, an "xhost" entry will appear with a pathname such as     "/usr/local/lib/xhost +". Remove this.SetUID and SetGID binaries (Unix systems)   On Unix systems, the "suid" bit on a system executable program allows   the program to execute as the owner. A program that is setUID to   "root" will allow the program to execute with root privileges. There   are multiple legitimate reasons for a program to have root   privileges, and many do. However, it may be unusual to have suid   programs in individual user directories or other non-system places. A   scan of the filesystems can turn up any program with its suid or sgid   bit set.  Before disabling any programs, check the legitimacy of the   files.Gwinn                        Informational                      [Page 5]

RFC 2179            Network Security For Trade Shows           July 1997   Tips:   * "find / -user root -perm -4000 -print" will find any occurrence of     a setuid file anywhere in the system, including those on NFS     mounted partitions.   * "find / -group kmem -perm -2000 -print" will do the same for kmem     group permissions.System Directory Ownership and Write Permissions   Check ownership of all system directories and permissions needed to   write or modify files. There is no simple way to do this on PC   operating systems like Windows NT without simply checking all files   and directories or using a version of "ls" that will list ACLs.   On Unix systems, a directory with permissions such as "drwxrwxrwx"   (such as /tmp) is world-writable and anyone can create or modify   files in such area. Pay special attention to "/" and "/etc". These   should be owned by some system account-not by an individual user.   When in doubt, contact the vendor of the system software for   confirmation of the appropriate directory or file permissions.Network Services   Any servers not needed should be disabled. The notorious "R services"   (rexec, rsh, and rlogin) are particularly prone to security problems   and should be disabled unless specifically needed.  Pay particular   attention to trusted hosts files, and be aware of the risk of IP   spoofing attacks from machines "pretending" to be trusted hosts.   Tips:   * On Unix systems, comment out "R services" (rexec, rsh, rlogin) in     /etc/inetd.conf.   * Check for other unknown or unneeded services.Trivial File Transfer Protocol (TFTP)   TFTP can be an easy way for an intruder to access system files. It is   good general practice to disable TFTP.  If TFTP is needed, verify   that only files targeted for export are accessible.  A simple way to   check security is to attempt to tftp files such as /etc/passwd or   /etc/motd to check accessiblity of system files.Gwinn                        Informational                      [Page 6]

RFC 2179            Network Security For Trade Shows           July 1997TCP Connection Monitoring   Public domain software (TCP Wrappers or "tcpd" for Unix systems)   allow restriction and monitoring of TCP connections on a host by host   basis. Systems can be configured to notify an administrator and   syslog when any unauthorized party attempts to access the host. This   software is available from:   *ftp://info.cert.org/pub/tools/tcp_wrappers/BIND (Berkeley Internet Name Daemon)   Earlier versions of BIND have been prone to various attacks. If a   host is going to be acting as DNS, use the latest version of BIND.   It is available at:   *ftp://ftp.isc.org/isc/bindSendmail and Mailer Security   A great number of previous versions of Sendmail have known security   holes.  Check installed sendmail for the most recent version.   Alternatively, consult the operating system vendor to get the most   recent release for the platform.Web Server Scripting Security   All Web server scripts and binaries should be checked (especially the   "...httpd/cgi-bin" directory) for those that allow shell commands to   be executed. Many attacks in recent months have focused on the use of   utilities such as "phf" for accessing /etc/passwd on a target system.   Remove any script that is not needed in the course of operation of a   web server.Other Suggestions   * Check with the vendor of the operating system for known security     issues. Make certain that all systems have the latest version of     software--especially security patches to fix specific problems.   * Examine log files on the host frequently. On Unix systems, the     "last" command will furnish information on recent logins and where     they came from. The "syslogs" or "Event Viewer" will contain more     specific information on system events.Gwinn                        Informational                      [Page 7]

RFC 2179            Network Security For Trade Shows           July 1997   * Web server logfiles (...httpd/log/access_log and     ...httpd/log/error_log) will contain information on who has been     accessing a WWW server, what has been accessed, and what has     failed.   * Good backups are the best defense against system damage. Perform     backups before placing a system on the trade show network then     continue backups throughout the show and again following the event.     A final backup set is useful to examine for possible attempts at     (or successful) penetrations of system security.General Network Security   As would be expected at network trade shows (large or otherwise),   there are many entities running packet sniffers. Most are exhibitors   who have a legitimate need to run them during the course of product   demonstrations. However, be aware that there are many "listening   ears" on network segments--any of whom can "hear" or "see"   information as it crosses the net. Particularly prone to   eavesdropping are telnet sessions. A good rule of thumb is to assume   that "when you type your password, the only one that doesn't see it   is you!"   It is a good practice to not log in (or "su") to an account with   privileges across the network if at all possible. As mentioned   previously, authentication tokens and ssh are a simple way to add   security to system account access.Packet Filtering   Many routers support basic packet filtering.  If a router can be   deployed between the local network and the show's network, general   basic packet filtering should be employed.  Below is a good "general"   packet filter approach. The approach itself is ordered into   categories:   * General global denials/acceptance.   * Specific global service denials.   * Specific service acceptance.   * Final denial of all other TCP/UDP services.   Based on the theory of denying everything that you don't know is   acceptable traffic, a good approach to a filter ruleset, in order of   execution priority, might be:Gwinn                        Informational                      [Page 8]

RFC 2179            Network Security For Trade Shows           July 1997   General Global Denials/Acceptance   1 Filter spoofed source addresses by interface. Match source     addresses to routing information available for the interface.     Discard packets with source addresses arriving on one interface     (from the "outside" for example) claiming a source address on     another interface (the "inside").   2 Filter all source routed packets unless source routing is     specifically needed.   3 Allow outbound connections from "inside" hosts.   4 Allow established TCP connections (protocol field contains 6 and     the TCP flags field either contains ACK or does NOT contain SYN     bit). Only filter requests for 'new' connections.   5 Filter 'new' connections with source port of 25. Prevents people     from pretending to be a remote mail server.   6 Filter loopback address (source address 127.0.0.1). Prevents     packets from a misconfigured DNS resolver.   Specific Global Service Denials   1 Specifically block all "R-command" ports     (destination ports 512-515).   2 Block telnet (destination port 23) from any host not requiring     telnet access from the outside. (If you use ssh, you can     block it from all hosts!)   3 Add specific filters to deny other specific protocols to the     network, as needed.   Specific Host/Service Acceptance   1 Add specific access to specific "public" hosts' services     (unsecure FTP or WWW servers).   2 Allow SMTP (source and destination port 25) for electronic mail     to the mail server(s).   3 Allow inbound FTP connections (source port 20) to the FTP server(s).   4 Allow DNS (source and destination port 53, UDP & TCP) to name servers.     If zone transfers are not needed, block the TCP ports.   5 Allow RIP packets in (source and destination port 520, UDP), if     appropriate.   6 Add specific filters to allow other desired specific protocols     or to open certain ports to specific machines.   Final Service Denial   1 Deny all other UDP and TCP services not allowed by the previous     filters.Gwinn                        Informational                      [Page 9]

RFC 2179            Network Security For Trade Shows           July 1997Author's Address   R. Allen Gwinn, Jr.   Associate Director, Computing   Business Information Center   Southern Methodist University   Dallas, TX  75275   Phone:  214/768-3186   EMail:  allen@mail.cox.smu.edu  or  allen@radio.netContributing Writer   Stephen S. Hultquist   President   Worldwide Solutions, Inc.   4450 Arapahoe Ave., Suite 100   Boulder, CO  80303   Phone: +1.303.581.0800   EMail: ssh@wwsi.comGwinn                        Informational                     [Page 10]