SPEERMINT Working Group S. Niccolini Internet-Draft NEC Intended status: Informational E. Chen Expires: March 2, 2008 NTT August 30, 2007 VoIP Security Threats relevant to SPEERMINT draft-niccolini-speermint-voipthreats-02 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 March 2, 2008. Copyright Notice Copyright (C) The IETF Trust (2007). Niccolini & Chen Expires March 2, 2008 [Page 1] Internet-Draft VoIP Threats August 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. Niccolini & Chen Expires March 2, 2008 [Page 2] Internet-Draft VoIP Threats August 2007 Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4 2. Security Threats relevant to SPEERMINT . . . . . . . . . . . . 5 2.1. Threats Relevant to the Location Function (LF) . . . . . . 5 2.1.1. Threats to LF Confidentiality . . . . . . . . . . . . 5 2.1.2. Threats to LF Integrity . . . . . . . . . . . . . . . 5 2.1.3. Threats to LF Availability . . . . . . . . . . . . . . 6 2.2. Threats to the Signaling Function (SF) . . . . . . . . . . 6 2.2.1. Threats to SF Confidentiality . . . . . . . . . . . . 6 2.2.2. Threats to SF Integrity . . . . . . . . . . . . . . . 7 2.2.3. Threats to SF Availability . . . . . . . . . . . . . . 8 2.3. Threats to the Media Function (MF) . . . . . . . . . . . . 9 2.3.1. Threats to MF Confidentiality . . . . . . . . . . . . 9 2.3.2. Threats to MF Integrity . . . . . . . . . . . . . . . 9 2.3.3. Threats to MF Availability . . . . . . . . . . . . . . 9 3. Security Best Practices . . . . . . . . . . . . . . . . . . . 11 3.1. General Security Best Practices . . . . . . . . . . . . . 11 3.2. Security Best Practices for the LF . . . . . . . . . . . . 11 3.2.1. Ensure LF Confidentiality . . . . . . . . . . . . . . 11 3.2.2. Ensure LF Integrity . . . . . . . . . . . . . . . . . 11 3.2.3. Ensure LF Availability . . . . . . . . . . . . . . . . 11 3.3. Security Best Practices for the SF . . . . . . . . . . . . 12 3.3.1. Ensure SF Confidentiality . . . . . . . . . . . . . . 12 3.3.2. Ensure SF Integrity . . . . . . . . . . . . . . . . . 12 3.3.3. Ensure SF Availability . . . . . . . . . . . . . . . . 12 3.4. Security Best Practices for the MF . . . . . . . . . . . . 12 3.4.1. Ensure MF Confidentiality and Integrity . . . . . . . 12 3.4.2. Ensure MF Availability . . . . . . . . . . . . . . . . 12 4. Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . 14 5. Security Considerations . . . . . . . . . . . . . . . . . . . 15 6. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 16 7. Informative References . . . . . . . . . . . . . . . . . . . . 17 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 18 Intellectual Property and Copyright Statements . . . . . . . . . . 19 Niccolini & Chen Expires March 2, 2008 [Page 3] Internet-Draft VoIP Threats August 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 March 2, 2008 [Page 4] Internet-Draft VoIP Threats August 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 Relevant to the Location Function (LF) 2.1.1. Threats to LF Confidentiality 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. 2.1.2. Threats to LF Integrity 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; Niccolini & Chen Expires March 2, 2008 [Page 5] Internet-Draft VoIP Threats August 2007 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 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. 2.1.3. Threats to LF Availability 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. 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. 2.2.1. Threats to SF Confidentiality o call pattern tracking - the attacker tracks the call patterns of the users violating his/her privacy; Niccolini & Chen Expires March 2, 2008 [Page 6] Internet-Draft VoIP Threats August 2007 2.2.2. Threats to SF Integrity 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 seesion hijacking - the attacker uses SIP messages (e.g. 301 Moved Temporarily) in order to hijack an existing call towards unexisting 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 comprimised. Another technique involves injecting faked BYE/CANCEL or error reponses to an ongoing dialogue in order to tear down a session or interrupt a session establishment. 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 inforation, 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 caller ID spoofing - the attacker spoofs the caller identifier in order to make calls avoiding paying for them. Niccolini & Chen Expires March 2, 2008 [Page 7] Internet-Draft VoIP Threats August 2007 o bypassing SF - the attacker sends the session intiation directly to the endpoint (Ua, media gateway, etc.) bypassing signaling entities in order to avoid paying for the used resources. 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. o illegitimate transit peers - multimedia traffic may be unknowningly delivered through an illegitimate transit peer. This introduces opportunities for a variety of attacks by rough peers. 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 spefication 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 unnecessarly 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 prenvented from establishing an SRTP session to secure privacy. 2.2.3. Threats to SF Availability 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 Niccolini & Chen Expires March 2, 2008 [Page 8] Internet-Draft VoIP Threats August 2007 and messages; 2.3. Threats to the Media Function (MF) Media function is responsible for the actual delivery of multimedia comunication 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 service assurance issues. This section discusses potential security threats to the media function to detail the possible attack vectors. 2.3.1. Threats to MF Confidentiality o eavesdropping - the attacker reconstruct the conversation and/or additional data delivered with it (e.g.numbers transmitted with DTMF tones); 2.3.2. Threats to MF Integrity 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 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 prenvented from establishing an SRTP session to secure privacy. 2.3.3. Threats to MF Availability 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 Niccolini & Chen Expires March 2, 2008 [Page 9] Internet-Draft VoIP Threats August 2007 experimented resulting in the usage of a poor quality codec degrading the overall quality of the call experience. Niccolini & Chen Expires March 2, 2008 [Page 10] Internet-Draft VoIP Threats August 2007 3. Security Best Practices This section will be completed in the next version 3.1. General Security Best Practices In the next version, this section will describe general security best practices such as the following. o source address assurance by ingress filtering o audit trail, trapping and logging o trusted time stamping o critical resource allocation o exception handling o system monitoring o mechanism to timely apply patches and supplementary code o separate network for management 3.2. Security Best Practices for the LF In the next version, this section will describe LF security best practices such as the following. 3.2.1. Ensure LF Confidentiality o Encryption o stripping proper headers at the border by SM/SBE 3.2.2. Ensure LF Integrity o authenticate DNS records with digital certificates [RFC 4033-4035] o strong authentication against intermediate nodes 3.2.3. Ensure LF Availability o server redundancy o filter illegitimate traffic Niccolini & Chen Expires March 2, 2008 [Page 11] Internet-Draft VoIP Threats August 2007 3.3. Security Best Practices for the SF In the next version, this section will describe SF security best practices such as the following. 3.3.1. Ensure SF Confidentiality o encryption 3.3.2. Ensure SF Integrity o encryption o Strong identity assertion o strong authentication against intermediate nodes o shared secret contact info between UA and server to prevent illegitimate INVITE packets 3.3.3. Ensure SF Availability o Fuzzing test against all devices before release o Mechanism to timely apply patches o Server redundancy o Rate limitation 3.4. Security Best Practices for the MF In the next version, this section will describe MF security best practices such as the following. 3.4.1. Ensure MF Confidentiality and Integrity o SRTP [requires consensus outside SPEERMINT on key exchange protocol] 3.4.2. Ensure MF Availability o Fuzzing test against all UA devices before release o DBEs provides policing based on active sessions (also cross-layer issue) Niccolini & Chen Expires March 2, 2008 [Page 12] Internet-Draft VoIP Threats August 2007 o verify whether packet rate is consistent with negotiated parameters Niccolini & Chen Expires March 2, 2008 [Page 13] Internet-Draft VoIP Threats August 2007 4. 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 March 2, 2008 [Page 14] Internet-Draft VoIP Threats August 2007 5. Security Considerations This memo is entirely focused on the security threats for SPEERMINT. Niccolini & Chen Expires March 2, 2008 [Page 15] Internet-Draft VoIP Threats August 2007 6. 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 March 2, 2008 [Page 16] Internet-Draft VoIP Threats August 2007 7. 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 March 2, 2008 [Page 17] Internet-Draft VoIP Threats August 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 March 2, 2008 [Page 18] Internet-Draft VoIP Threats August 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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Information on the procedures with respect to rights in RFC documents can be found in BCP 78 and BCP 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 at http://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. Acknowledgment Funding for the RFC Editor function is provided by the IETF Administrative Support Activity (IASA). Niccolini & Chen Expires March 2, 2008 [Page 19]