SPEERMINT Working Group S. Niccolini Internet-Draft NEC Intended status: Informational E. Chen Expires: September 2, 2007 NTT March 1, 2007 VoIP Security Threats relevant to SPEERMINT draft-niccolini-speermint-voipthreats-01 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 September 2, 2007. Copyright Notice Copyright (C) The IETF Trust (2007). Niccolini & Chen Expires September 2, 2007 [Page 1] Internet-Draft VoIP Threats March 2007 Abstract This memo presents the different security threats related to SPEERMINT classifying them into threats to the Location Function, to the Signaling Function and to the Media Function. The different instances of the threats are briefly introduced inside the classification. Finally the existing security solutions in SIP and RTP/RTCP are presented to describe the countermeasures currently available for such threats. The objective of this document is to identify and enumerate the SPEERMINT-specific threat vectors in order to specify security-related requirements. Once the requirements are identified, methods and solutions how to achieve such requirements can be selected. Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 2. Security Threats relevant to SPEERMINT . . . . . . . . . . . . 4 2.1. Threats to the Location Function (LF) . . . . . . . . . . 4 2.2. Threats to the Signaling Function (SF) . . . . . . . . . . 5 2.2.1. Denial of Service Attacks to SF . . . . . . . . . . . 6 2.2.2. Fraud . . . . . . . . . . . . . . . . . . . . . . . . 7 2.2.3. Federation Policy Violation . . . . . . . . . . . . . 7 2.2.4. Negotiation Modification/Interruption in Signaling . . 8 2.3. Threats to the Media Function (MF) . . . . . . . . . . . . 8 2.3.1. Denial of Service Attacks to MF . . . . . . . . . . . 9 2.3.2. Privacy Infringement . . . . . . . . . . . . . . . . . 9 2.4. Social Threats . . . . . . . . . . . . . . . . . . . . . . 10 3. Overview of SPEERMINT security requirements . . . . . . . . . 11 4. Overview of Security Solutions . . . . . . . . . . . . . . . . 12 5. Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . 14 6. Security Considerations . . . . . . . . . . . . . . . . . . . 15 7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 16 8. Informative References . . . . . . . . . . . . . . . . . . . . 17 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 18 Intellectual Property and Copyright Statements . . . . . . . . . . 19 Niccolini & Chen Expires September 2, 2007 [Page 2] Internet-Draft VoIP Threats March 2007 1. Introduction With VoIP, the need for security is compounded because there is the need to protect both the control plane and the data plane. In a legacy telephone system, security is a more valid assumption. Intercepting conversations requires either physical access to telephone lines or to compromise the Public Switched Telephone Network (PSTN) nodes or the office Private Branch eXchanges (PBXs). Only particularly security-sensitive organizations bother to encrypt voice traffic over traditional telephone lines. In contrast, the risk of sending unencrypted data across the Internet is more significant (e.g. DTMF tones corresponding to the credit card number). An additional security threat to Internet Telephony comes from the fact that the signaling is sent using the same network as the multimedia data; traditional telephone systems have the signaling network separated from the data network. This is an increased security threat since a hacker could attack the signaling network and its servers with increased damage potential (call hijacking, call drop, DoS attacks, etc.). Therefore there is the need of investigating the different security threats, to extract security- related requirements and to highlight the solutions how to protect from such threats. Niccolini & Chen Expires September 2, 2007 [Page 3] Internet-Draft VoIP Threats March 2007 2. Security Threats relevant to SPEERMINT This section enumerates potential security threats relevant to SPEERMINT. A taxonomy of VoIP security threats is defined in [1]. Such a taxonomy is really comprehensive and takes into account also non-VoIP-specific threats (e.g. loss of power, etc.). Threats relevant to the boundaries of layer-5 SIP networks are extracted from such a taxonomy and mapped to the classification relevant for the SPEERMINT architecture as defined in [2], moreover additional threats for the SPEERMINT architecture are listed and detailed under the same classification: o Location Function (LF); o Signaling Function (SF); o Media Function (MF). An additional category is also included for completeness to address social threats relevant to SPEERMINT even if they are currently out of the scope of the SPEERMINT charter. 2.1. Threats to the Location Function (LF) There are a number of potential security threats to the development of call routing data (CRD) by discovering the Signaling Function (SF) and end user's reachable host. o routing directories modification - the attacker modifies routing directories (e.g. DNS, ENUM tree, etc.) in an unauthorized way in order to modify the call routing. The scope could be to reroute the call inserting unauthorized nodes in the path, to exclude authorized nodes from the path, to route the call towards a wrong destination causing a Denial of Service (DoS), to route the call towards a wrong destination causing annoyance for the callee; o call routing modification by Man in the Middle (MitM) - the attacker has already or inserts an unauthorized node in the signaling path in order to modify the call routing. The scope could be to reroute the call inserting other unauthorized nodes in the path, to exclude authorized nodes from the path, to route the call towards a wrong destination causing a Denial of Service (DoS), to route the call towards a wrong destination causing annoyance for the callee; o DNS and ENUM hijacking - the attacker uses a technique called cache poisoning that exploits a flaw in the DNS software and tricks the server into receiving incorrect information. The Niccolini & Chen Expires September 2, 2007 [Page 4] Internet-Draft VoIP Threats March 2007 compromised server would cache and serve the incorrect information locally. This technique can be used to replace arbitrary NAPTR records for a set of ENUM queries with NAPTR records of an attacker's choosing. This allows the attacker to redirect all calls to a malicious destination. o proxy impersonation - the attacker tricks a SIP UA or proxy into communicating with a rogue proxy. VoIP calls established among different peering providers may introduce a number of new opportunities for such attack as intermediate proxies are discovered dynamically during call routing. A successful proxy impersonation allows full access and control to all routed SIP messages. o Denial of Service Attacks to LF - A DoS attack to the location function is possible by sending a large number of queries to the associated ENUM gateways or DNS servers. This prevents a User Agent to look up the NAPTR record of the intended recipient of the call. o identity theft - the attacker uses the identity of the owner without the consent for the scope of masking his real identity when committing fraud (e.g. when calling the attacker can charge the bill of the identity owner, the attacker can use the identity to bypass call blocking, etc.); o numbers/identities harvesting - the attacker harvests numbers and/or user identities by issuing a multitude of location requests with the purpose of discovering the existent ones and their identifiers/addresses for calling them, for using them as spoofed identities or just for retrieving their location in the physical topology; o signaling entities harvesting - the attacker harvests signaling entities (SIP Proxy Servers, etc.) addresses by issuing a specific number of requests with the purpose of discovering their location in the physical topology or for targeting them with subsequent attacks. 2.2. Threats to the Signaling Function (SF) Signaling function involves a great number of sensitive information. Through signaling function, user agents (UA) assert identities and VSP operators authorize billable resources. Correct and trusted operations of signaling function is essential for service providers. This section discusses potential security threats to the signaling function to detail the possible attack vectors. Niccolini & Chen Expires September 2, 2007 [Page 5] Internet-Draft VoIP Threats March 2007 2.2.1. Denial of Service Attacks to SF There are a number of ways to conduct a Denial of Service attack to the signaling function. o SIP malformed requests and messages - the attacker tries to cause a crash or a reboot of the proxy/endpoint by sending SIP malformed requests and messages; o SIP requests and messages flooding - the attacker tries to exhaust the resources of the proxy/endpoint by sending many SIP requests and messages; o session black holing - the attacker intentionally drops essential packets (e.g. INVITE) of the VoIP protocol resulting the call initiation to fail, it is needed that the attacker controls (or is) a node in the middle of the signaling path; o session tear down - the attacker uses CANCEL/BYE messages in order to tear down an existing call at SIP layer, it is needed that the attacker replicates the proper SIP header for the hijacking to be successful (To, From, Call-ID, CSeq); o session hijacking - the attacker uses SIP messages (e.g. 301 Moved Temporarily) in order to hijack an existing call towards non- existing proxy/endpoint to make the session initiation fail, it is needed that the attacker replicates the proper SIP header for the hijacking to be successful (To, From, Call-ID, CSeq); o SIP message spoofing - There are a number of ways to perform a DoS attack by spoofing SIP messages. An attacker may directly send initial INVITE messages to a User Agent that has no capability to authenticate them. Such messages may cause the UA to ring non- stop and effectively make it unusable. Moreover, if the INVITE appears to come from a SIP server, the UA may keep responding to the server with multiple messages. This may cause a DrDoS (Distributed Reflection DoS) attack to the SIP server if enough UAs are compromised. In principle such attacks does not need interception of any packet in order to be performed (could be done by simple guessing) but some of these attacks (e.g. session hijacking, session tear down, etc.) benefit from the retrieval of call-specific information as coming from interception of SIP packets. Niccolini & Chen Expires September 2, 2007 [Page 6] Internet-Draft VoIP Threats March 2007 2.2.2. Fraud There are a number of ways to commit a fraud by exploiting vulnerabilities in the signaling function: o accounting fraud by media oversize - the attacker injects in the network more traffic than declared in the session request in order to avoid paying for the used resources; o session replay - the attacker replays a past session of another user in order to have access to the same resources (e.g. a bank account, etc.). This attack can results in using resources without paying for them, having access to sensitive information, loss of money, etc.; o call hijacking - the attacker uses SIP messages (e.g. 301 Moved Temporarily) in order to hijack an existing call towards other proxy/endpoint, it is needed that the attacker replicates the proper SIP header for the hijacking to be successful (To, From, Call-ID, CSeq); o call pattern tracking - the attacker tracks the call patterns of the users violating his/her privacy; o caller ID spoofing - the attacker spoofs the caller identifier in order to make calls avoiding paying for them. o bypassing SF - the attacker sends the session initiation directly to the endpoint (Ua, media gateway, etc.) bypassing signaling entities in order to avoid paying for the used resources. 2.2.3. Federation Policy Violation VoIP carriers that allow session peering through a federation are expected to establish some form of explicit policies to be adhered by all members. These policies may normally include terms such as capacity controls and identity assertion. Members with lower security level may bring new threats to the federation and thus affect all participating carriers. o weak caller ID assertion by peers - a carrier member fails to achieve the level of identity assertion expected by the federation may introduce an entry point for attackers to conduct CID (caller ID) spoofing fraud. This would affect all members in the federation, despite their efforts to strengthen the assertion within their own domains. Niccolini & Chen Expires September 2, 2007 [Page 7] Internet-Draft VoIP Threats March 2007 o overwhelming traffic from peers - a carrier member with a large number of UAs infected by bots or worms may unintentionally transmit traffic floods to other peers in the federation and violate the capacity control policy of the federation. o illegitimate transit peers - multimedia traffic may be unknowingly delivered through an illegitimate transit peer. This introduces opportunities for a variety of attacks by rough peers. 2.2.4. Negotiation Modification/Interruption in Signaling The signaling function is used to perform, among the others, session and protocol capabilities negotiation as well as key exchange among parties involved in a call session. There are a variety of ways that an attacker can compromise such negotiations. o codec negotiation interruption/modification - signaling function is used to perform handshake regarding the codec(s) to be used during multimedia session. An attacker may intentionally drop or modify only packets involved in the handshake. This attack could interrupt the multimedia communication or degrade the quality achievable in the case o lower quality codec is used. o SIP protocol specification interruption/modification - signaling function may use specific details of the signaling protocol. Extensions and the signaling associated may vary. An attacker may intentionally drop or modify only packets meant to give evidence or declare such extensions tricking the peering party into wrong assumptions. This attack could make the peering party wrongly allocating protocol mediation function resulting in failure to establish communications or parts of them. Moreover the peering party would unnecessarily use resources in allocating such protocol mediation function resulting in a DoS attack. o bid-down attack to SF - a number of encryption key exchange protocols performs handshake through the Signaling Function. An attacker may intentionally drop or modify only packets involved in the handshake. While this attack does not interrupt the voice communication, calling parties are prevented from establishing an SRTP session to secure privacy. 2.3. Threats to the Media Function (MF) Media function is responsible for the actual delivery of multimedia communication between the users and carries sensitive information. Through media function, user agents (UA) can establish secure communications and monitor quality of conversations. Correct and trusted operations of media function is essential for privacy and Niccolini & Chen Expires September 2, 2007 [Page 8] Internet-Draft VoIP Threats March 2007 service assurance issues. This section discusses potential security threats to the media function to detail the possible attack vectors. 2.3.1. Denial of Service Attacks to MF There are a number of ways to conduct a Denial of Service attack to the media function. o RTP/RTCP malformed messages - the attacker tries to cause a crash or a reboot of the proxy/endpoint by sending RTP/RTCP malformed messages; o RTP/RTCP messages flooding - the attacker tries to exhaust the resources of the proxy/endpoint by sending many RTP/RTCP messages; o RTP/RTCP session tear down - the attacker uses RTCP messages (e.g. BYE) in order to tear down an existing call at RTP layer, the SIP layer will not notice that the RTP flow has been torn down and the call will not result as released; o RTP/RTCP QoS degradation - the attacker sends wrong RTCP reports advertising more packet loss or more jitter than actually experimented resulting in the usage of a poor quality codec degrading the overall quality of the call experience. In principle such attacks does not need interception of any packet in order to be performed (could be done by simple guessing) but some of these attacks (e.g. call hijacking, RTP/RTCP session tear down, etc.) benefit from the retrieval of call-specific information as coming from interception of SIP/RTP/RTCP packets. 2.3.2. Privacy Infringement The media function is responsible for enabling private conversation between parties involved in a call session. There are a variety of ways that an attacker can compromise the privacy of VoIP conversations. o eavesdropping - the attacker reconstruct the conversation and/or additional data delivered with it (e.g.numbers transmitted with DTMF tones); o media alteration - the attacker alters some RTP packets in order to modify the conversation between two users; o bid-down attack to MF - a number of encryption key exchange protocols performs handshake through the Media Function. ZRTP [3] is an example of such protocol that exchanges key information Niccolini & Chen Expires September 2, 2007 [Page 9] Internet-Draft VoIP Threats March 2007 using RTP at the beginning before establishing an SRTP session. An attacker may intentionally drop only RTP packets involved in the handshake. While this attack does not interrupt the voice communication, calling parties are prevented from establishing an SRTP session to secure privacy. 2.4. Social Threats False presentation of information together with unwanted contact are the only social threats that can be reconducted to a technical background in the case of VoIP. Examples are: o VoIP phishing - VoIP phishing involves an attacker creating a phone number that appears to represent a legitimate organization such as a bank. VoIP allows an attacker to easily set up a malicious IVR (Interactive Voice Response) system with a toll-free number that is harder to trace than one set up on PSTN. This type of fraud may be more effective than email-based phising since victims tend to trust more a phone number than a URL; o unwanted lawful/unlawful contact - the attacker contacts the victim with the unlawful or lawful scopes (e.g. extortion, telemarketing, etc.), please note that unwanted lawful contact in the case of VoIP is also referred to as SPam over Internet Telephony (SPIT), SPIT discussion is excluded by the SPEERMINT working group per charter. Niccolini & Chen Expires September 2, 2007 [Page 10] Internet-Draft VoIP Threats March 2007 3. Overview of SPEERMINT security requirements This section will discuss the SPEERMINT security requirements as outcome of the threat overview given in Section 2. The requirements will be then enable the selection of the security solutions to be adopted by SPEERMINT in order to meet the identified requirements. Niccolini & Chen Expires September 2, 2007 [Page 11] Internet-Draft VoIP Threats March 2007 4. Overview of Security Solutions This section presents the VoIP security features currently standardized or under standardization in order to give an overview of the building blocks needed to counter the VoIP Security threats detailed in this draft. The technology to secure VoIP can be divided in three main areas as follows: o Authentication/Authorization; o Encryption; o Identity management. Authentication is needed to understand who was the sender of a specific packet. Authentication can take place between different entities or end-to-end: o from client to server - Digest authentication [4] or mutual Transport Layer Security (TLS) [5]; o from server to server - mutual Transport Layer Security (TLS); o from server to client - Transport Layer Security (TLS); o end-to-end - S/MIME [6]. All solutions require some kind of trust relationship (i.e. shared secret or certificates authorities). Encryption is needed to protect the content of the packets from being read by other parties than the ones which are supposed to be the recipient of such packets. Encryption follows the same paradigm as authentication and can be done either on a hop-by-hop or on a end-to- end basis. On a hop-by-hop basis TLS is used (TLS creates an authenticated, encrypted, integrity-checked channel). On a end-to- end basis S/MIME is used to sign and encrypt portions of the SIP body. At the media level a end-to-end encryption is possible using SRTP [7] to protect RTP/RTCP media (audio, video). Currently there is a discussion in the IETF about the requirements for SRTP media keying which is still an open issue. Other solutions that provide encryption and integrity are lower layer ones like IPsec which is done hop-by-hop. Identity management is also an important piece of security framework in SIP [8]. The objective of the identity framework is to give technical means to assess user identity in a secure manner. It requires strong cryptographic assertions but it represents the most Niccolini & Chen Expires September 2, 2007 [Page 12] Internet-Draft VoIP Threats March 2007 promising approach to enable further security solutions which need the assumption of dealing with strong authenticated identities. Please note that other techniques could also be used to counter VoIP Security threats, the techniques that constitute stand-alone solutions and that do not need standardization work are left out the scope of this document. It is left open for discussion which other security techniques to include in this section. Niccolini & Chen Expires September 2, 2007 [Page 13] Internet-Draft VoIP Threats March 2007 5. Conclusions This memo presented a the different SPEERMINT security threats classified in groups related to the Location Function, Signaling Function and Media Function respectively. The multiple instances of the threats are presented with a brief explanation. Finally the existing security solutions in VoIP were presented to describe the countermeasures currently available for such threats. The objective of this document is to identify and enumerate the VoIP threat vectors in order to specify security-related requirements specific to SPEERMINT (that will be included in section Section 3). Once the requirements are identified, methods and solutions how to achieve such requirements can be selected. Niccolini & Chen Expires September 2, 2007 [Page 14] Internet-Draft VoIP Threats March 2007 6. Security Considerations This memo is entirely focused on the security threats for SPEERMINT. Niccolini & Chen Expires September 2, 2007 [Page 15] Internet-Draft VoIP Threats March 2007 7. Acknowledgements This memo takes inspiration from VOIPSA VoIP Security and Privacy Threat Taxonomy. The author would like to thank VOIPSA for having produced such a comprehensive taxonomy which is the starting point of this draft. The author would also like to thank Cullen Jennings for the useful slides presented at the VoIP Management and Security workshop in Vancouver. Niccolini & Chen Expires September 2, 2007 [Page 16] Internet-Draft VoIP Threats March 2007 8. Informative References [1] "VOIPSA VoIP Security and Privacy Threat Taxonomy", October 2005. [2] Penno, R., Hammer, M., Khan, S., Malas, D., and A. Uzelac, "SPEERMINT Peering Architecture", draft-ietf-speermint-architecture-02.txt (work in progress), October 2006. [3] Zimmermann, P., Johnston, A., and J. Callas, "ZRTP: Extensions to RTP for Diffie-Hellman Key Agreement for SRTP", draft-zimmermann-avt-zrtp-02.txt (work in progress), October 2006. [4] Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston, A., Peterson, J., Sparks, R., Handley, M., and E. Schooler, "SIP: Session Initiation Protocol", RFC 3261, June 2002. [5] Dierks, T. and E. Rescorla, "The TLS Protocol Version 1.2", draft-ietf-tls-rfc4346-bis-02.txt (work in progress), October 2006. [6] Ramsdell, B., "Secure/Multipurpose Internet Mail Extensions (S/MIME) Version 3.1 Message Specification", RFC 3851, July 2004. [7] Baugher, M., McGrew, D., Naslund, M., Carrara, E., and K. Norrman, "The Secure Real-time Transport Protocol (SRTP)", RFC 3711, March 2004. [8] Peterson, J. and C. Jennings, "Enhancements for Authenticated Identity Management in the Session Initiation Protocol (SIP)", RFC 4474, August 2006. Niccolini & Chen Expires September 2, 2007 [Page 17] Internet-Draft VoIP Threats March 2007 Authors' Addresses Saverio Niccolini Network Laboratories, NEC Europe Ltd. Kurfuersten-Anlage 36 Heidelberg 69115 Germany Phone: +49 (0) 6221 4342 118 Email: saverio.niccolini@netlab.nec.de URI: http://www.netlab.nec.de Eric Chen Information Sharing Platform Laboratories, NTT 3-9-11 Midori-cho Musashino, Tokyo 180-8585 Japan Email: eric.chen@lab.ntt.co.jp URI: http://www.ntt.co.jp/index_e.html Niccolini & Chen Expires September 2, 2007 [Page 18] Internet-Draft VoIP Threats March 2007 Full Copyright Statement Copyright (C) The IETF Trust (2007). This document is subject to the rights, licenses and restrictions contained in BCP 78, and except as set forth therein, the authors retain all their rights. 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