SIPPING Jaeduck Choi Internet Draft Souhwan Jung Intended status: Informational Yujung Jang Expires: May 15, 2008 Soongsil University Yoojae Won Youngduk Cho KISA November 16, 2007 Experiments on SPIT in the Commercial VoIP Services draft-choi-sipping-experiments-spit-01.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 May 15, 2008. Copyright Notice Copyright (C) The IETF Trust (2007). Choi, et al. Expires May 15, 2008 [Page 1] Internet-Draft Experiments on SPIT November 2007 Abstract This document shows some experimental results on SPIT on commercial VoIP services, in which a SIP UA has not been secured by SIP security protocol such as TLS. Although many service providers have been applying the HTTP digest scheme to authenticate a SIP UA, they often do not apply SIP signaling protection against potential threats between the SIP UA and the SIP proxy. This cause vulnerabilities to the VoIP services like SPIT. The aim of this memo is to inform the service providers of SPIT threats by showing some experimental results of SPIT on current VoIP networks. Table of Contents 1. Introduction...................................................2 2. Terminology....................................................4 3. Experiments on SPIT............................................4 3.1. The SPIT between the UAC and the Outbound Proxy...........5 3.2. The SPIT between the Inbound Proxy and the UAS............6 3.3. The SPIT between the Outbound Proxy and the Inbound Proxy.7 3.4. The SPIT using Replay Attack..............................8 3.5. The SPIT using Dictionary Attack.........................10 4. Security Considerations.......................................10 5. IANA Considerations...........................................10 6. References....................................................11 6.1. Normative References.....................................11 6.2. Informative References...................................11 Author's Addresses...............................................12 Intellectual Property Statement..................................13 Disclaimer of Validity...........................................13 Copyright Statement..............................................14 Acknowledgment...................................................14 1. Introduction The SPIT (SPam over Internet Telephony) [2] can be classified into two categories: the SPIT sent on path associated with SIP signaling and off path. The SPIT sent on path associated with SIP signaling means that a spammer who registered the VoIP service sends the SPIT message. For sending SPIT, spammers SHOULD register a VoIP service, and then could send a SPIT only through normal signaling routes. The studies on Choi, et al. Expires May 15, 2008 [Page 2] Internet-Draft Experiments on SPIT November 2007 protecting this SPIT have been discussed in several drafts [4][5][6][7][8] at the SIPPING WG. The SPIT on sip signaling route is out of the scope of this draft. In case of the abnormal routes, a spammer who did not register to the VoIP services tries to send the SPIT message using replay attack, dictionary attack, or sniffing. It is not easy for spammers to send this SPIT if the security mechanisms specified in the SIP protocol [3] are applied to all the signaling routes in SIP: among the UA, proxy, registrar, and so on. In many cases, however, the TLS mechanism is not applied between the SIP nodes, this SPIT still works between the UA and the SIP proxy or the SIP proxy servers. The spammer can send SIP messages like INVITE or 200 OK directly to the UA or the SIP proxy, and then communicate with the user by establishing a media channel. Currently, VoIP providers have been applying only the HTTP digest scheme to authenticate a UA. They do not consider protecting SIP signaling between the UA and the SIP proxy. On the commercial networks where the TLS mechanism is not applied, some SPIT scenarios were tested as follows. - The SPIT between the UAC and the Outbound Proxy - The SPIT between the Inbound Proxy and the UAS - The SPIT between the Outbound Proxy and the Inbound Proxy - The SPIT using Replay Attack - The SPIT using Dictionary Attack Although both the UA and the spammer belong to the same local area network during experiments, it is possible for the spammer with sophisticated spywares or monitoring tools to send a SPIT to the remote users. The goal of this document is to inform service providers of potential SPIT threats by showing some experimental results on SPIT on current VoIP networks so that they SHOULD carefully consider applying the TLS mechanism to the SIP UA. Choi, et al. Expires May 15, 2008 [Page 3] Internet-Draft Experiments on SPIT November 2007 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 RFC-2119 [1]. Two terminologies are defined in this document. A normal route in SPIT: The SPIT sent through a normal signaling route by a spammer who registered the VoIP service. An abnormal route in SPIT: The SPIT sent through an abnormal signaling route by a spammer who did not register the VoIP service. 3. Experiments on SPIT The experiments are performed on the following networks. - Three commercial VoIP providers - Three commercial UAs and two open UAs There is no TLS mechanism applied among the UAC, UAS, and Proxy servers. Also, the UA and the spammer belong to the same LAN so that the spammer can sniff SIP messages and send them directly to the UA. +-------------+ +-------------------------+ +-------------+ | LAN A | | Internet | | LAN B | | | | | | | |+---+ | | +--------+ +--------+ | | +---+| || | | | |Outbound| |Inbound | | | | || ||UAC|--------|--|-| Proxy |---| Proxy |-|--|--------|UAS|| |+---+ | | | +--------+ | +--------+ | | | +---+| | | | | | | | | | | +---+---+ | | +---+---+ | | +---+---+ | | |Spammer| | | |Spammer| | | |Spammer| | | +-------+ | | +-------+ | | +-------+ | +-------------+ +-------------------------+ +-------------+ Figure 1 : Configuration of SPIT Testbed Choi, et al. Expires May 15, 2008 [Page 4] Internet-Draft Experiments on SPIT November 2007 3.1. The SPIT between the UAC and the Outbound Proxy This experiment shows that the spammer sends a 200 OK response to the UAC in complying with an INVITE message initiated by an UA as a call request to the UAS. Figure 2 shows the message flow of our experiment. When the spammer senses the INVITE message, he generates a 200 OK message, spoofs IP address of the proxy server, and then replies with the 200 OK message. Upon receiving the 200 OK message, the media channel might be established between the UAC and the spammer. As a result, the spammer could play out a recorded announcement or communicate with the UAS. In the experiment, this SPIT succeeded at all the tested UAs. UAC Outbound Proxy Inbound Proxy UAS | | | | | INVITE | | | |------------------>| | | | 407 | | | |<------------------| | | | ACK | | | |------------------>| | | | INVITE(Credential)| | | |------------------>| INVITE | | | |------------------>| INVITE | | Spammer | |------------------>| | | | | | | 200 OK | | | | |<--------| | | | | ACK | | | | |-------->| | | | | RTP | | | 180 Ring | |<=======>| | 180 Ring |<------------------| | 180 Ring |<------------------| 200 OK | Ingnore<---------------| 200 OK |<------------------| | 200 OK |<------------------| | Ingnore<---------------| | | | | | | | Figure 2 : The Message Flow of the SPIT between the UAC and the Proxy This SPIT was possible because the spammer could easily sniff the INVITE message. If the TLS mechanism is used between the UA and proxy server, this SPIT can be protected. Choi, et al. Expires May 15, 2008 [Page 5] Internet-Draft Experiments on SPIT November 2007 3.2. The SPIT between the Inbound Proxy and the UAS This scenario that spammers can directly send SIP calls to the UAS using P2P call signaling has been discussed on the draft [9]. This document shows an experimental result using this scenario on commercial VoIP networks. Figure 3 shows the message flow of our experiment. To make a direct call, the spammer generates an INVITE message and sends it to the UAS. The spammer needs to sniff the 200 OK message from the UAS. The 200 OK message includes the IP address and port number for media session. Upon sniffing the 200 OK, the spammer could play out a recorded announcement or communicate with the UAS. In our test, this SPIT worked at all the UA's. Also, the one-ring SPIT is tested. In this case, the spammer sends only the INVITE message without sniffing the corresponding 200 OK message. When the UAS receives the INVITE message, the phone is ringing and the SIP URI is displayed at the user. The user who feels curious about the name ID might make a return call to the caller. Consequently, the spammer can make a successful talk with the callee. This SPIT also worked at all the UAs during our experiments. UAC Outbound Proxy Inbound Proxy UAS | | | | | | | Spammer | | | | | | | | | | INVITE | | | | |-------->| | | | |180 Ring | | | Ignore<----------------| | | | | 200 OK | | | Ignore<----------------| | | | | ACK | | | | |-------->| | | | | RTP | | | | |<=======>| | | | | | Figure 3 : The Message Flow of the SPIT between the Proxy and the UA This SPIT was also possible because the TLS was not established between the proxy server and the UAS. If the TLS was applied to the UAS, the INVITE message sent by the spammer could be blocked during the TLS process. Hence, the INVITE message could be dropped. Choi, et al. Expires May 15, 2008 [Page 6] Internet-Draft Experiments on SPIT November 2007 3.3. The SPIT between the Outbound Proxy and the Inbound Proxy Without using the TLS between SIP servers, the spammer who impersonates a legitimate outbound proxy server can send a SPIT message via inbound proxy server of the UAS. This is similar to the SPIT between the inbound proxy and UAS. Figure 4 shows the message flow of our experiment. First of all, the spammer generates the INVITE message including the information of the legitimate outbound proxy server and the UAC, and then sends the message to the inbound proxy. The inbound proxy server normally handles this message. After sending the INVITE message, the spammer performs the same procedure as the section 3.2. As a result, the spammer could play out a recorded announcement or communicate with the UAS. In the experiment, this SPIT succeeded in the environment where the TLS is not applied between the proxy servers. UAC Outbound Proxy Inbound Proxy UAS | | | | | | Spammer | | | | | | | | | | INVITE | | | | |-------->| INVITE | | | | |------------------>| | | | | 180 Ring | | | |180 Ring |<------------------| | Ingnore<---------------| | | | | | 200 OK | | | | 200 OK |<------------------| | Ingnore<---------------| | | | | ACK | | | | |-------->| ACK | | | | |------------------>| | | | | RTP | | | |<===========================>| | | | | | Figure 4 : The Message Flow of the SPIT between the Outbound Proxy and Inbound Proxy This SPIT was also possible because the TLS was not established between the proxy servers. If the TLS was applied to the proxy server, the spammer could not send the SIP messages. Choi, et al. Expires May 15, 2008 [Page 7] Internet-Draft Experiments on SPIT November 2007 3.4. The SPIT using Replay Attack This SPIT is that the spammer tries to send a SPIT message using replay attack after terminating the session between the UAC and UAS. Figure 5 shows the message flow of our experiment. For sending SPIT, the spammer should sniff the INVITE message including a credential. The spammer sends the BYE message to the UAS to terminate the established session. And then, the spammer tries to send the sniffed INVITE message including the credential. This SPIT worked at all the VoIP providers during our experiments. Choi, et al. Expires May 15, 2008 [Page 8] Internet-Draft Experiments on SPIT November 2007 UAC Outbound Proxy Inbound Proxy UAS | | | | |INVITE (Credential)| | | | (spammer sniffing)| | | |------------------>| INVITE | | | |------------------>| INVITE | | | |------------------>| | | | 180 Ring | | | 180 Ring |<------------------| | 180 Ring |<------------------| 200 OK | |<------------------| 200 OK |<------------------| | 200 OK |<------------------| | |<------------------| | | | Spammer | | | | | BYE | | | | |-------->| BYE | | | | |------------------>| BYE | | | | |------------------>| : : : : : | | INVITE | | | | |(Credential) | | | |-------->| INVITE | | | | |------------------>| INVITE | | | | |------------------>| | | | | 180 Ring | | | | 180 Ring |<------------------| | |180 Ring |<------------------| 200 OK | |<------------------| 200 OK |<------------------| | | 200 OK |<------------------| | Ingnore <--------------| | | | | ACK | | | | |-------->| ACK | | | | |------------------>| ACK | | | | |------------------>| | | | RTP | | |<=========================================================>| | | | | | Figure 5 : The Message Flow of the SPIT Using Replay attack This SPIT was possible because the TLS was not established between the UAC and outbound proxy server, and the digest authentication scheme was not applied to the BYE message. If the TLS or digest scheme was applied to the UAC, the spammer could not send the SIP messages. Choi, et al. Expires May 15, 2008 [Page 9] Internet-Draft Experiments on SPIT November 2007 3.5. The SPIT using Dictionary Attack The spammer can send a SPIT message to the UA through normal routes without revealing his position and privacy information. When the TLS is not used at the UA, the spammer can apply the dictionary attack with credential value obtained by sniffing to guess the legitimate password. If the attack is successful, the spammer can make a call spam via normal routes in SIP network without disclosing any of his information. Anybody could easily sniff the REGISTER or INVITE messages on the deployed VoIP networks. They could also guess the legitimate password of a UA using dictionary attack tools. For the reason, VoIP service providers SHOULD apply the TLS mechanism between the UA and the SIP server such as registrar and proxy server. 4. Security Considerations This document showed some experimental results on feasible SPIT scenarios on commercial VoIP networks. Spammers might try to directly send SPIT to the UA or proxy server, on abnormal routes in SIP-based networks. If the TLS mechanism is used among the UAC, proxy, registrar, and UAS, these SPIT can be protected. The VoIP providers, however, have not been applying the TLS mechanism at the UA or proxy servers. Hence, the SPIT worked at all the commercial UAs during our experiments. Although our experiments were performed at the situation that both commercial UA and spammer belong to the same local area network, it is possible for the spammer to send a SPIT to a remote UA using spyware or hacking tools. Therefore, it is necessary for service providers to apply strictly the TLS mechanism to the UA and proxy server. If the TLS is used, it is difficult for spammers who want to know information for establishing media session to sniff the SIP messages. The authentication value can be protected by the same reason. 5. IANA Considerations This document does not require actions by IANA. Choi, et al. Expires May 15, 2008 [Page 10] Internet-Draft Experiments on SPIT November 2007 6. References 6.1. Normative References [1] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. 6.2. Informative References [2] Rosenberg, J., and Jennings, C., "The Session Initiation Protocol (SIP) and Spam", draft-ietf-sipping-spam-05, July 2007. [3] Rosenberg, J., Schulzrinne, H., Camarillo, G., Jonston, A., Peterson, J., Sparks, R., Handley, M., and E. Schooler, "SIP: Session Initiation Protocol", RFC 3261, June 2002. [4] Hannes, T., Geoffrey, D., Thomas, F., Dan, W., and Henning, S., "Requirements for Authorization Policies to tackle Spam for Internet Telephony and Unwanted Trafic", draft-froment-sipping- spit-requirements-01, July 2007. [5] Saverio, N. and Juergen, Q., "signaling To Prevent SPIT (SPITSTOP) Reference Scenario", draft-niccolini-sipping- spitstop, January 2007. [6] Geoffrey, D., Thomas, F., and Hannes, T., "Authorization Policies for Preventing SPIT", draft-froment-sipping-spit- authz-policies-02, February 2007. [7] Saverio, N., Sandra, T., Martin, S., and Samir, S. "SIP Extensiions for SPIT Identification", draft-niccolini-sipping- feedback-spit-03, February 2007. [8] Hannes, T., Henning, S., Dan, W., Jonathan, R., and David, S. "A Framewor for Reducing Spam for Internet Telephony", draft- tschofenig-sipping-framework-spit-reduction-01, July 2007. [9] Jung, S., Choi, J., Won, Y., and Cho, Y., "Authentication between the Inbound Proxy and the UAS for Protecting SPIT in the Session Initiation Protocol (SIP)", draft-jung-sipping- authentication-spit-00, October 2006. Choi, et al. Expires May 15, 2008 [Page 11] Internet-Draft Experiments on SPIT November 2007 Author's Addresses Jaeduck Choi Soongsil University 511, Sangdo-dong, Dongjak-ku Seoul 156-743 KOREA Phone: +82-2-824-1807 Email: cjduck@cns.ssu.ac.kr Souhwan Jung Soongsil University 511, Sangdo-dong, Dongjak-ku Seoul 156-743 KOREA Phone: +82-2-820-0714 Email: souhwanj@ssu.ac.kr Yujung Jang Soongsil University 511, Sangdo-dong, Dongjak-ku Seoul 156-743 KOREA Phone: +82-2-824-1807 Email: lilyuwjd@cns.ssu.ac.kr Yoojae Won Korea Information Security Agency 78, Karak-dong, Songpa-Gu Seoul 138-160 KOREA Phone: +82-2-405-5548 Email: yjwon@kisa.or.kr Choi, et al. Expires May 15, 2008 [Page 12] Internet-Draft Experiments on SPIT November 2007 Youngduk Cho Korea Information Security Agency 78, Karak-dong, Songpa-Gu Seoul 138-160 KOREA Phone: +82-2-405-5548 Email: ydcho@kisa.or.kr Intellectual Property Statement 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 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. Disclaimer of Validity 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. Choi, et al. Expires May 15, 2008 [Page 13] Internet-Draft Experiments on SPIT November 2007 Copyright Statement Copyright (C) The Internet 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. Acknowledgment Funding for the RFC Editor function is currently provided by the Internet Society. Choi, et al. Expires May 15, 2008 [Page 14]