Memory leak in Cisco IOS 12.2, 12.4, 15.0, and 15.1, when Zone-Based Policy Firewall SIP application layer gateway inspection is enabled, allows remote attackers to cause a denial of service (memory consumption or device reload) via malformed SIP messages, aka Bug ID CSCtl99174.
http://tools.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-20130327-cce