Memory leak in the Session Initiation Protocol (SIP) implementation in Cisco IOS 12.2 through 12.4, when VoIP is configured, allows remote attackers to cause a denial of service (memory consumption and voice-service outage) via unspecified valid SIP messages.
https://oval.cisecurity.org/repository/search/definition/oval%3Aorg.mitre.oval%3Adef%3A5927
http://www.vupen.com/english/advisories/2008/2670
http://www.cisco.com/en/US/products/products_security_advisory09186a0080a01562.shtml