Internet DRAFT - draft-choi-sipping-experiments-spit
draft-choi-sipping-experiments-spit
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
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Copyright (C) The IETF Trust (2007).
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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
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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.
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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
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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.
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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.
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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.
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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.
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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.
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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.
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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.
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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
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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
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