ECRIT H. Tschofenig Internet-Draft Siemens Expires: August 18, 2006 H. Schulzrinne Columbia U. M. Shanmugam Siemens T. Taylor Nortel February 14, 2006 Security Threats and Requirements for Emergency Call Mapping draft-taylor-ecrit-security-threats-02.txt Status of this Memo By submitting this Internet-Draft, each author represents that any applicable patent or other IPR claims of which he or she is aware have been or will be disclosed, and any of which he or she becomes aware will be disclosed, in accordance with Section 6 of BCP 79. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF), its areas, and its working groups. Note that other groups may also distribute working documents as Internet- Drafts. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." The list of current Internet-Drafts can be accessed at http://www.ietf.org/ietf/1id-abstracts.txt. The list of Internet-Draft Shadow Directories can be accessed at http://www.ietf.org/shadow.html. This Internet-Draft will expire on August 18, 2006. Copyright Notice Copyright (C) The Internet Society (2006). Abstract This document reviews the security threats to the process of mapping locations to URIs pointing to Public Safety Answering Points (PSAPs). This mapping occurs as part of the process of routing emergency calls Tschofenig, et al. Expires August 18, 2006 [Page 1] Internet-Draft ECRIT Security Requirements February 2006 through the IP network. Based on the threats, this document establishes a set of security requirements for the mapping protocol, which is being developed by the ECRIT Working Group. Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4 3. Mapping and the emergency call routing process . . . . . . . . 5 4. Motivations of attackers . . . . . . . . . . . . . . . . . . . 6 5. Potential attacks . . . . . . . . . . . . . . . . . . . . . . 7 5.1. Attacks to prevent a specific individual from receiving aid . . . . . . . . . . . . . . . . . . . . . . 7 5.2. Attacks to gain information about an emergency . . . . . . 7 5.3. Attacks to gain fraudulent use of ASP/VSP services . . . . 8 5.4. Attacks against the emergency response system . . . . . . 9 6. Security requirements relating to emergency call routing . . . 10 7. Security Considerations . . . . . . . . . . . . . . . . . . . 11 8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 12 9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 13 10. References . . . . . . . . . . . . . . . . . . . . . . . . . . 14 10.1. Normative References . . . . . . . . . . . . . . . . . . . 14 10.2. Informative References . . . . . . . . . . . . . . . . . . 14 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 15 Intellectual Property and Copyright Statements . . . . . . . . . . 16 Tschofenig, et al. Expires August 18, 2006 [Page 2] Internet-Draft ECRIT Security Requirements February 2006 1. Introduction Legacy telephone network (PSTN) users can summon help for emergency services such as ambulance, fire and police using a well known unique 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. As one of the steps to achieve this, a protocol must be developed allowing a client entity to submit a location and receive a URI pointing to the applicable PSAP for that location. Attacks against the PSTN (many focussing on free calling) 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. In view of the mandate of the ECRIT Working Group, the present document restricts itself to attacks on the mapping of locations to PSAP URIs. This document is organized as follows: Section 2 describes basic terminology. Section 3 briefly describes how mapping fits within the process of routing emergency calls. Section 4 describes some motivations of attackers in the context of ECRIT, Section 5 describes and illustrates the attacks that might be used, and Section 6 lists the security-related requirements that must be met if these attacks are to be mitigated. Tschofenig, et al. Expires August 18, 2006 [Page 3] Internet-Draft ECRIT Security Requirements February 2006 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. Application (Voice) Service Provider (ASP/VSP), mapping service, emergency address, emergency caller, emergency identifier, mapping, mapping client, mapping server, mapping protocol, and Public Safety Answering Point (PSAP) are taken from [I-D.ecrit-requirements]. Location information is taken from RFC 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. Tschofenig, et al. Expires August 18, 2006 [Page 4] Internet-Draft ECRIT Security Requirements February 2006 3. Mapping and the emergency call routing process The first 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 [I-D.ecrit-requirements], 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 receive back a URI which can be used to direct call signalling to a PSAP. Since mapping requires location information for input, when and where the location information is acquired constrains when mapping can be done and which devices can act as mapping clients. The key distinction in "when" is before the emergency or during the emergency. The key distinction in "where" is at the emergency caller's device or at another device in the signalling path between the emergency caller and the PSAP. The device that acquires the location information can be the mapping client, and so can any device downstream of that point. It is even possible for a PSAP itself to initiate mapping, to determine whether an arriving call should be handled by a call taker at that PSAP or should be proxied to another PSAP. Tschofenig, et al. Expires August 18, 2006 [Page 5] Internet-Draft ECRIT Security Requirements February 2006 4. Motivations of attackers Attackers may direct their efforts either against an individual or against a portion of the emergency response system. Attacks against an individual fall into three 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; o attacks by the caller to gain fraudulent use of ASP/VSP services, by using an Emergency Identifier to bypass normal authentication, authorization, and accounting procedures. Attacks against the emergency response system are aimed either at denying system services to all users in a given area, or at diverting emergency responders to non-emergency sites. The latter motivation falls outside the scope of this analysis. One interesting variant on the "system denial" motivation is the case where a victim of a large emergency hopes to gain faster service by blocking others' competing calls for help. Tschofenig, et al. Expires August 18, 2006 [Page 6] Internet-Draft ECRIT Security Requirements February 2006 5. Potential attacks This section describes classes of attacks on the mapping process that could be used to achieve the attacker goals described in the previous section. 5.1. Attacks to prevent a specific individual from receiving aid This section discusses blocking attacks directed at a specific individual. The more general blocking attacks described in Section 5.4 will also operate to the same effect. They are discussed separately because the separation may be useful when weighing the priority for implementing specific defenses. Blocking attacks against an individual can operate against the operation of the mapping protocol, or through impersonation of the mapping server. It is also possible that the mapping protocol is used indirectly to interfere with other aspects of the emergency call process. The basic attacks available against protocol operation are denial of service, interference through message insertion, and interference through man-in-the middle alteration of messages. Denial of service can be achieved in several ways: by flooding attacks on the client or server, by taking control of the mapping client, by installing filters on the channel, or by installing filters at the mapping server. Man-in-the-middle attacks also involve taking control of the channel or the mapping server. The attacks based on control of the mapping server can also be carried out using impersonation of the mapping server. This may be an easier attack to execute in some circumstances. The mapping protocol may also be used to support a reflection attack on the mapping client or on some other component of the routing chain. To execute this attack, the attacker impersonates the target when sending requests to the mapping server. 5.2. 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). 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., news Tschofenig, et al. Expires August 18, 2006 [Page 7] Internet-Draft ECRIT Security Requirements February 2006 reporter, "ambulance chaser"). The primary information that interceptions of mapping requests and responses will reveal are a location, a URI identifying a PSAP, 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 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 interception of the media stream between the caller and the PSAP. 5.3. Attacks to gain fraudulent use of ASP/VSP services This section discusses attacks whereby the Emergency Caller is hoping to bypass normal procedures to achieve free use of ASP/VSP services. An attack of this sort is possible only if the following conditions are true: a. The attacker is the emergency caller. b. The attacker has control over the addressing of the emergency call request either as a result of or subsequent to the mapping operation. c. The call enters the domain of an ASP/VSP, which accepts it without applying normal requirements for an authenticated subscriber identity because it is marked as an emergency call. d. The ASP/VSP routes it according to the called address (e.g., SIP Request-URI), without verifying that this is the address of a PSAP. The key condition is the second one. The attacker has two possibilities for controlling the addressing of the call. One is to insert a false entry into the mapping database for the caller's location, allowing the caller free calls to wherever the entry points to. The second possibility comes if the emergency caller's device is the mapping client. In this case, if the caller reprograms the device to accept an arbitrary input in place of the URI returned by the mapping process, the caller is able to complete a call to that URI while bypassing the ASP/VSP's normal authentication procedures. Tschofenig, et al. Expires August 18, 2006 [Page 8] Internet-Draft ECRIT Security Requirements February 2006 5.4. 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. The motivation may range from thoughtless vandalism, to wide-scale criminality, to terrorism. The possible attacks on the mapping process to achieve this have already been described; they simply have to be less targeted. The attacks are denial of service or misdirection through provision of incorrect responses to mapping queries. The mechanisms are flooding attacks (for denial of service only), control of the Mapping Server, or impersonation of the Mapping Server. Tschofenig, et al. Expires August 18, 2006 [Page 9] Internet-Draft ECRIT Security Requirements February 2006 6. Security requirements relating to emergency call routing This section describes the security requirements which must be fulfilled in the mapping protocol to prevent or blunt the effectiveness of the attacks described in the previous section. Attack: flooding attack on the mapping client, mapping server, or a third entity. Requirement: The mapping protocol MUST NOT create new opportunities for flooding attacks, including amplification attacks. Attack: insertion of interfering messages. Requirement: The protocol MUST permit the mapping client to verify that the response is a response to the query it sent out. Attack: man-in-the-middle alteration of messages. Requirement: The protocol MUST permit the application of the integrity service to requests and responses as an implementation option. Attack: impersonation of the mapping server. Requirement: the protocol MUST permit the mapping client to authenticate the mapping server as an implementation option. Attack: snooping of location and other information. Requirement: the protocol MUST permit the use of the confidentiality service as an implementation option. Attack: fraudulent calls. Requirement: the protocol MUST permit the reverse lookup of URIs to verify that a URI corresponds to a PSAP in the mapping database. Note - the necessity to use this capability depends on whether the system architecture satisfies the conditions listed in Section 5.3. If the emergency caller's device is not the mapping client, the opportunity for fraud is very much limited. Tschofenig, et al. Expires August 18, 2006 [Page 10] Internet-Draft ECRIT Security Requirements February 2006 7. Security Considerations This document addresses security threats and security requirements. Therefore, security is considered throughout this document. Tschofenig, et al. Expires August 18, 2006 [Page 11] Internet-Draft ECRIT Security Requirements February 2006 8. Acknowledgements Hannes Tschofenig performed the initial security analysis for ECRIT. The authors would like to thank Stephen Kent for his extensive comments on previous issues of this document, which led to a complete rewriting of it. Tschofenig, et al. Expires August 18, 2006 [Page 12] Internet-Draft ECRIT Security Requirements February 2006 9. IANA Considerations This document does not require actions by the IANA. Tschofenig, et al. Expires August 18, 2006 [Page 13] Internet-Draft ECRIT Security Requirements February 2006 10. References 10.1. Normative References [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. 10.2. Informative References [I-D.ecrit-requirements] Schulzrinne, H. and R. Marshall, "Requirements for Emergency Context Resolution with Internet Technologies", February 2006. [RFC3693] Cuellar, J., Morris, J., Mulligan, D., Peterson, J., and J. Polk, "Geopriv Requirements", RFC 3693, February 2004. Tschofenig, et al. Expires August 18, 2006 [Page 14] Internet-Draft ECRIT Security Requirements February 2006 Authors' Addresses Hannes Tschofenig Siemens Otto-Hahn-Ring 6 Munich, Bayern 81739 Germany Email: Hannes.Tschofenig@siemens.com Henning Schulzrinne Columbia University Department of Computer Science 450 Computer Science Building New York, NY 10027 USA Phone: +1 212 939 7042 Email: schulzrinne@cs.columbia.edu URI: http://www.cs.columbia.edu/~hgs Murugaraj Shanmugam Siemens Otto-Hahn-Ring 6 Munich, Bayern 81739 Germany Email: murugaraj.shanmugam@siemens.com Tom Taylor Nortel 1852 Lorraine Ave Ottawa, Ontario K1H 6Z8 Canada Email: taylor@nortel.com Tschofenig, et al. 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