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Network Working Group                                     T. Taylor, Ed.Request for Comments: 5069                                        NortelCategory: Informational                                    H. Tschofenig                                                  Nokia Siemens Networks                                                          H. Schulzrinne                                                     Columbia University                                                            M. Shanmugam                                                                 Detecon                                                            January 2008Security Threats and Requirements forEmergency Call Marking and MappingStatus 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 document reviews the security threats associated with the   marking of signalling messages to indicate that they are related to   an emergency, and with the process of mapping locations to Universal   Resource Identifiers (URIs) that point to Public Safety Answering   Points (PSAPs).  This mapping occurs as part of the process of   routing emergency calls through the IP network.   Based on the identified threats, this document establishes a set of   security requirements for the mapping protocol and for the handling   of emergency-marked calls.Taylor, et al.               Informational                      [Page 1]

RFC 5069              ECRIT Security Requirements           January 2008Table of Contents1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .22.  Terminology  . . . . . . . . . . . . . . . . . . . . . . . . .33.  Marking, Mapping, and the Emergency Call Routing Process . . .33.1.  Call Marking . . . . . . . . . . . . . . . . . . . . . . .33.2.  Mapping  . . . . . . . . . . . . . . . . . . . . . . . . .44.  Objectives of Attackers  . . . . . . . . . . . . . . . . . . .45.  Potential Attacks  . . . . . . . . . . . . . . . . . . . . . .55.1.  Attacks Involving the Emergency Identifier . . . . . . . .55.2.  Attacks Against or Using the Mapping Process . . . . . . .55.2.1.  Attacks Against the Emergency Response System  . . . .6       5.2.2.  Attacks to Prevent a Specific Individual from               Receiving Aid  . . . . . . . . . . . . . . . . . . . .75.2.3.  Attacks to Gain Information about an Emergency . . . .7   6.  Security Requirements Relating to Emergency Marking and       Mapping  . . . . . . . . . . . . . . . . . . . . . . . . . . .87.  Security Considerations  . . . . . . . . . . . . . . . . . . .98.  Acknowledgements . . . . . . . . . . . . . . . . . . . . . . .109.  References . . . . . . . . . . . . . . . . . . . . . . . . . .109.1.  Normative References . . . . . . . . . . . . . . . . . . .109.2.  Informative References . . . . . . . . . . . . . . . . . .101.  Introduction   Legacy telephone network users can summon help for emergency services   (such as an ambulance, the fire department, and the police) using a   well known number (e.g., 911 in North America, 112 in Europe).  A key   factor in the handling of such calls is the ability of the system to   determine caller location and to route the call to the appropriate   Public Safety Answering Point (PSAP) based on that location.  With   the introduction of IP-based telephony and multimedia services,   support for emergency calling via the Internet also has to be   provided.  Two core components of IP-based emergency calling include   an emergency service identifier and a mapping protocol.  The   emergency service identifier indicates that the call signaling   establishes an emergency call, while the mapping protocol translates   the emergency service identifier and the caller's geographic location   into an appropriate PSAP URL.   Attacks against the Public Switched Telephone Network (PSTN) have   taken place for decades.  The Internet is seen as an even more   hostile environment.  Thus, it is important to understand the types   of attacks that might be mounted against the infrastructure providing   emergency services and to develop security mechanisms to counter   those attacks.  While this can be a broad topic, the present document   restricts itself to attacks on the mapping of locations to PSAP URIs   and attacks based on emergency marking.  Verification by the PSAPTaylor, et al.               Informational                      [Page 2]

RFC 5069              ECRIT Security Requirements           January 2008   operator of the truthfulness of a reported incident and various other   attacks against the PSAP infrastructure related to the usage of faked   location information are outside the scope of the document.   This document is organized as follows:Section 2 describes basic   terminology.Section 3 briefly describes how emergency marking and   mapping fit within the process of routing emergency calls.Section 4   describes some motivations of attackers in the context of emergency   calling,Section 5 describes and illustrates the attacks that might   be used, andSection 6 lists the security-related requirements that   must be met if these attacks are to be mitigated.2.  Terminology   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this   document are to be interpreted as described in [RFC2119], with the   qualification that unless otherwise stated, they apply to the design   of the mapping protocol, not its implementation or application.   The terms "call taker", "mapping service", "emergency caller",   "emergency identifier", "mapping", "mapping client", "mapping   server", "mapping protocol", and "Public Safety Answering Point   (PSAP)" are taken from [RFC5012].   The term "location information" is taken fromRFC 3693 [RFC3693].   The term "emergency caller's device" designates the IP host closest   to the emergency caller in the signalling path between the emergency   caller and the PSAP.  Examples include an IP phone running SIP,   H.323, or a proprietary signalling protocol, a PC running a soft   client or an analogue terminal adapter, or a residential gateway   controlled by a softswitch.3.  Marking, Mapping, and the Emergency Call Routing Process   This memo deals with two topics relating to the routing of emergency   calls to their proper destination: call marking and mapping.3.1.  Call Marking   Marking of call signalling enables entities along the signalling path   to recognize that a particular signalling message is associated with   an emergency call.  Signalling containing the emergency identifier   may be given priority treatment, special processing, and/or special   routing.Taylor, et al.               Informational                      [Page 3]

RFC 5069              ECRIT Security Requirements           January 20083.2.  Mapping   An important goal of emergency call routing is to ensure that any   emergency call is routed to a PSAP.  Preferably, the call is routed   to the PSAP responsible for the caller's location, since misrouting   consumes valuable time while the call taker locates and forwards the   call to the right PSAP.  As described in [RFC5012], mapping is part   of the process of achieving this preferable outcome.   In brief, mapping involves a mapping client, a mapping server, and   the protocol that passes between them.  The protocol allows the   client to pass location information to the mapping server and to   receive back a URI, which can be used to direct call signalling to a   PSAP.4.  Objectives of Attackers   Attackers may direct their efforts either against a portion of the   emergency response system or against an individual.  Attacks against   the emergency response system have three possible objectives:   o  to deny system services to all users in a given area.  The      motivation may range from thoughtless vandalism, to wide-scale      criminality, to terrorism.  One interesting variant on this      motivation is the case where a victim of a large emergency hopes      to gain faster service by blocking others' competing calls for      help.   o  to gain fraudulent use of services, by using an emergency      identifier to bypass normal authentication, authorization, and      accounting procedures.   o  to divert emergency calls to non-emergency sites.  This is a form      of a denial-of-service attack similar to the first item, but quite      likely more confusing for the caller himself or herself since the      caller expects to talk to a PSAP operator but instead gets      connected to someone else.   Attacks against an individual fall into two classes:   o  attacks to prevent an individual from receiving aid.   o  attacks to gain information about an emergency that can be applied      either against an individual involved in that emergency or to the      profit of the attacker.Taylor, et al.               Informational                      [Page 4]

RFC 5069              ECRIT Security Requirements           January 20085.  Potential Attacks5.1.  Attacks Involving the Emergency Identifier   The main possibility of attack involves use of the emergency   identifier to bypass the normal procedures in order to achieve   fraudulent use of services.  An attack of this sort is possible only   if the following conditions are true:   a.  The attacker is the emergency caller.   b.  The call routing system assumes that the emergency caller's       device signals the correct PSAP URI for the caller's location.   c.  The call enters the domain of a service provider, which accepts       it without applying normal procedures for authentication and       authorization because the signalling carries the emergency       identifier.   d.  The service provider routes the call according to the called       address (e.g., SIP Request-URI), without verifying that this is       the address of a PSAP (noting that a URI by itself does not       indicate the nature of the entity it is pointing to).   If these conditions are satisfied, the attacker can bypass normal   service provider authorization procedures for arbitrary destinations,   simply by reprogramming the emergency caller's device to add the   emergency identifier to non-emergency call signalling.  In this case,   the call signalling most likely will not include any location   information, or there could be location information, but it is false.   An attacker wishing to disrupt the emergency call routing system may   use a similar technique to target components of that system for a   denial-of-service attack.  The attacker will find this attractive to   reach components that handle emergency calls only.  Flooding attacks   are the most likely application of the technique, but it may also be   used to identify target components for other attacks by analyzing the   content of responses to the original signalling messages.5.2.  Attacks Against or Using the Mapping Process   This section describes classes of attacks involving the mapping   process that could be used to achieve the attacker goals described inSection 4.Taylor, et al.               Informational                      [Page 5]

RFC 5069              ECRIT Security Requirements           January 20085.2.1.  Attacks Against the Emergency Response System   This section considers attacks intended to reduce the effectiveness   of the emergency response system for all callers in a given area.  If   the mapping operation is disabled, then the emergency caller's device   might not have the correct PSAP URI.  As a consequence, the   probability that emergency calls will be routed to the wrong PSAP   increases.  In the worst case, the emergency caller's device might   not be able to obtain a PSAP URI at all.  Routing to the wrong PSAP   has a double consequence: emergency response to the affected calls is   delayed, and PSAP call taker resources outside the immediate area of   the emergency are consumed due to the extra effort required to   redirect the calls.  Alternatively, attacks that cause the client to   receive a URI that does not lead to a PSAP have the immediate effect   of causing emergency calls to fail.   Three basic attacks on the mapping process can be identified: denial   of service, impersonation of the mapping server, or corruption of the   mapping database.  Denial of service can be achieved in several ways:   o  by a flooding attack on the mapping server;   o  by taking control of the mapping server and either preventing it      from responding or causing it to send incorrect responses; or   o  by taking control of any intermediary node (for example, a router)      through which the mapping queries and responses pass, and then      using that control to block them.  An adversary may also attempt      to modify the mapping protocol signalling messages.  Additionally,      the adversary may be able to replay past communication exchanges      to fool an emergency caller by returning incorrect results.   In an impersonation attack, the attacker induces the mapping client   to direct its queries to a host under the attacker's control rather   than the real mapping server, or the attacker suppresses the response   from the real mapping server and sends a spoofed response.   The former type of impersonation attack itself is an issue of mapping   server discovery rather than the mapping protocol directly.  However,   the mapping protocol may allow impersonation to be detected, thereby   preventing acceptance of responses from an impersonating entity and   possibly triggering a more secure discovery procedure.   Corruption of the mapping database cannot be mitigated directly by   mapping protocol design.  Once corruption has been detected, the   mapping protocol may have a role to play in determining which records   have been corrupted.Taylor, et al.               Informational                      [Page 6]

RFC 5069              ECRIT Security Requirements           January 2008   Beyond these attacks on the mapping operation itself, it is possible   to use mapping to attack other entities.  One possibility is that   mapping clients are misled into sending mapping queries to the target   of the attack instead of the mapping server.  Prevention of such an   attack is an operational issue rather than one of protocol design.   Another possible attack is where the mapping server is tricked into   sending responses to the target of the attack through spoofing of the   source address in the query.5.2.2.  Attacks to Prevent a Specific Individual from Receiving Aid   If an attacker wishes to deny emergency service to a specific   individual, the mass attacks described inSection 5.2.1 will   obviously work provided that the target individual is within the   affected population.  Except for the flooding attack on the mapping   server, the attacker can in theory limit these attacks to the target,   but this requires extra effort that the attacker is unlikely to   expend.  If the attacker is using a mass attack but does not wish to   have too broad an effect, it is more likely to attack for a carefully   limited period of time.   If the attacker wants to be selective, however, it may make more   sense to attack the mapping client rather than the mapping server.   This is particularly so if the mapping client is the emergency   caller's device.  The choices available to the attacker are similar   to those for denial of service on the server side:   o  a flooding attack on the mapping client;   o  taking control of any intermediary node (for example, a router)      through which the mapping queries and responses pass, and then      using that control to block or modify them.   Taking control of the mapping client is also a logical possibility,   but raises no issues for the mapping protocol.5.2.3.  Attacks to Gain Information about an Emergency   This section discusses attacks used to gain information about an   emergency.  The attacker may be seeking the location of the caller   (e.g., to effect a criminal attack).  Alternatively, the attacker may   be seeking information that could be used to link an individual (the   caller or someone else involved in the emergency) with embarrassing   information related to the emergency (e.g., "Who did the police take   away just now?").  Finally, the attacker could be seeking to profit   from the emergency, perhaps by offering his or her services (e.g., a   news reporter, or a lawyer aggressively seeking new business).Taylor, et al.               Informational                      [Page 7]

RFC 5069              ECRIT Security Requirements           January 2008   The primary information that interceptions of mapping requests and   responses will reveal are a location, a URI identifying a PSAP, the   emergency service identifier, and the addresses of the mapping client   and server.  The location information can be directly useful to an   attacker if the attacker has high assurance that the observed query   is related to an emergency involving the target.  The type of   emergency (fire, police, or ambulance) might also be revealed by the   emergency service identifier in the mapping query.  The other pieces   of information may provide the basis for further attacks on emergency   call routing, but because of the time factor, are unlikely to be   applicable to the routing of the current call.  However, if the   mapping client is the emergency caller's device, the attacker may   gain information that allows for interference with the call after it   has been set up or for interception of the media stream between the   caller and the PSAP.6.  Security Requirements Relating to Emergency Marking and Mapping   This section describes the security requirements that must be   fulfilled to prevent or reduce the effectiveness of the attacks   described inSection 5.  The requirements are presented in the same   order as the attacks.   FromSection 5.1:   Attack A1: fraudulent calls.   Requirement R1: For calls that meet conditions a) to c) ofSection 5.1, the service provider's call routing entity MUST verify   that the destination address (e.g., SIP Request-URI) presented in the   call signalling is that of a PSAP.   Attack A2: Use of emergency identifier to probe in order to identify   emergency call routing entities for attack by other means.   Requirement: None identified, beyond the ordinary operational   requirement to defend emergency call routing entities by means such   as firewalls and, where possible, authentication and authorization.   FromSection 5.2.1:   Attack A3: Flooding attack on the mapping client, mapping server, or   a third entity.   Requirement R2: The mapping protocol MUST NOT create new   opportunities for flooding attacks, including amplification attacks.Taylor, et al.               Informational                      [Page 8]

RFC 5069              ECRIT Security Requirements           January 2008   Attack A4: Insertion of interfering messages.   Requirement R3: The protocol MUST permit the mapping client to verify   that the response it receives is responding to the query it sent out.   Attack A5: Man-in-the-middle modification of messages.   Requirement R4: The mapping protocol MUST provide integrity   protection of requests and responses.   Requirement R5: The mapping protocol or the system within which the   protocol is implemented MUST permit the mapping client to   authenticate the source of mapping responses.   Attack A6: Impersonation of the mapping server.   Requirement R6: The security considerations for any discussion of   mapping server discovery MUST address measures to prevent   impersonation of the mapping server.   Requirement R5 also follows from this attack.   Attack A7: Corruption of the mapping database.   Requirement R7: The security considerations for the mapping protocol   MUST address measures to prevent database corruption by an attacker.   Requirement R8: The protocol SHOULD include information in the   response that allows subsequent correlation of that response with   internal logs that may be kept on the mapping server, to allow   debugging of mis-directed calls.   FromSection 5.2.2: No new requirements.   FromSection 5.2.3:   Attack A8: Snooping of location and other information.   Requirement R9: The protocol and the system within which it is   implemented MUST maintain confidentiality of the request and   response.7.  Security Considerations   This document addresses security threats and security requirements.   Therefore, security is considered throughout this document.Taylor, et al.               Informational                      [Page 9]

RFC 5069              ECRIT Security Requirements           January 20088.  Acknowledgements   The writing of this document has been a task made difficult by the   temptation to consider the security concerns of the entire personal   emergency calling system, not just the specific pieces of work within   the scope of the ECRIT Working Group.  Hannes Tschofenig performed   the initial security analysis for ECRIT, but it has been shaped since   then by the comments and judgement of the ECRIT WG at large.  At an   earlier stage in the evolution of this document, Stephen Kent of the   Security Directorate was asked to review it and provided extensive   comments, which led to a complete rewriting of it.  Brian Rosen,   Roger Marshall, Andrew Newton, and most recently, Spencer Dawkins,   Kamran Aquil, and Ron Watro have also provided detailed reviews of   this document at various stages.  The authors thank them.   We would like to thank Donald Eastlake for his review on behalf of   the Security Area Directorate and Christian Vogt for his review as   part of the General Area Review Team.   Finally, we would like to thank Jari Arkko, Jon Peterson, and Russ   Housley for their IETF Last Call comments.9.  References9.1.  Normative References   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate              Requirement Levels",BCP 14,RFC 2119, March 1997.9.2.  Informative References   [RFC3693]  Cuellar, J., Morris, J., Mulligan, D., Peterson, J., and              J. Polk, "Geopriv Requirements",RFC 3693, February 2004.   [RFC5012]  Schulzrinne, H. and R. Marshall, Ed., "Requirements for              Emergency Context Resolution with Internet Technologies",RFC 5012, January 2008.Taylor, et al.               Informational                     [Page 10]

RFC 5069              ECRIT Security Requirements           January 2008Authors' Addresses   Tom Taylor (editor)   Nortel   1852 Lorraine Ave   Ottawa, Ontario  K1H 6Z8   Canada   EMail: tom.taylor@rogers.com   Hannes Tschofenig   Nokia Siemens Networks   Otto-Hahn-Ring 6   Munich, Bavaria  81739   Germany   EMail: Hannes.Tschofenig@nsn.com   URI:http://www.tschofenig.com   Henning Schulzrinne   Columbia University   Department of Computer Science   450 Computer Science Building   New York, NY  10027   US   Phone: +1 212 939 7004   EMail: hgs+ecrit@cs.columbia.edu   URI:http://www.cs.columbia.edu   Murugaraj Shanmugam   Detecon International GmbH   Oberkasseler str 2   Bonn, NRW  53227   Germany   EMail: murugaraj.shanmugam@detecon.comTaylor, et al.               Informational                     [Page 11]

RFC 5069              ECRIT Security Requirements           January 2008Full Copyright Statement   Copyright (C) The IETF Trust (2008).   This document is subject to the rights, licenses and restrictions   contained inBCP 78, and except as set forth therein, the authors   retain all their rights.   This document and the information contained herein are provided on an   "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS   OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY, THE IETF TRUST AND   THE INTERNET ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS   OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF   THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED   WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.Intellectual Property   The IETF takes no position regarding the validity or scope of any   Intellectual Property Rights or other rights that might be claimed to   pertain to the implementation or use of the technology described in   this document or the extent to which any license under such rights   might or might not be available; nor does it represent that it has   made any independent effort to identify any such rights.  Information   on the procedures with respect to rights in RFC documents can be   found inBCP 78 andBCP 79.   Copies of IPR disclosures made to the IETF Secretariat and any   assurances of licenses to be made available, or the result of an   attempt made to obtain a general license or permission for the use of   such proprietary rights by implementers or users of this   specification can be obtained from the IETF on-line IPR repository athttp://www.ietf.org/ipr.   The IETF invites any interested party to bring to its attention any   copyrights, patents or patent applications, or other proprietary   rights that may cover technology that may be required to implement   this standard.  Please address the information to the IETF at   ietf-ipr@ietf.org.Taylor, et al.               Informational                     [Page 12]