Information leak vulnerabilities in SIP implementations

The use of VoIP as a cheaper communications alternative is growing at an astronomical rate. However, potential abuse of the technology may hinder its deployment. One key security concern is the exploitation of implementation vulnerabilities in the form of unauthorized access, worms, viruses, and denial of service attacks, particularly when combined with explicit targeting of implementations that are known to be vulnerable. One way to protect from exploitations of implementation-specific vulnerabilities is "security-by-obscurity" where a SIP device does not reveal its specific software version. For the same reason, the SIP standard does not encourage announcing the software version in SIP messages. In this article we show that even when SIP messages do not explicitly contain software version information, there is sufficient information leak to determine it. To demonstrate this, we introduce techniques to fingerprint SIP devices and develop a fingerprinting tool called SIPProbe that collects fingerprints and identifies SIP implementations. This type of information leak presents a new security concern as it can be used by malicious users as a building block to scan SIP devices and launch attacks