Unspecified vulnerability in the SIP implementation in Cisco IOS 12.3 and 12.4 allows remote attackers to execute arbitrary code via a malformed SIP message, aka Bug ID CSCsz89904, the "SIP Packet Parsing Arbitrary Code Execution Vulnerability."
http://www.cisco.com/en/US/products/products_security_advisory09186a0080b20f32.shtml
http://tools.cisco.com/security/center/viewAlert.x?alertId=20065