Security clearing house CERT this week warned of "numerous vulnerabilities" in multiple vendors' implementations of the Session Initiation Protocol (SIP), an important standard for next-generation Internet telephony systems.

SIP is used to initiate communication and data sessions between users and it is riddled with potential problems, it emerges.

"These vulnerabilities may allow an attacker to gain unauthorized privileged access, cause denial-of-service attacks, or cause unstable system behaviour", CERT warns.

The flaws came to light after Oulu University Secure Programming Group (OUSPG) ran a series of tests on a variety of SIP-enabled products. Most of the problems identified relate to the INVITE message, which is used in setting up sessions.

OUSPG's previous testing work led to vulnerability advisories on LDAP and SNMP, so its work is to be taken seriously.

The vulnerabilities identified with SIP are fairly esoteric and, according to security researchers, are not yet being actively exploited. So we have a little breathing space.

This is just as well as many vendors' products are potentially affected. CERT helpfully provides links to advisories by vendors of the subject and mitigation advice, which you can find here.

An advisory by Cisco supplies more background and an insight into how much work may be needed to guard against vulnerabilities involving SIP. Many vendors, including Microsoft, are still researching the extent to which the issue affects their products. ®