Unspecified vulnerability in the NAT implementation in Cisco IOS 12.1 through 12.4 and 15.0 through 15.1, and IOS XE 3.1.xSG, allows remote attackers to cause a denial of service (device reload or hang) by sending crafted SIP packets to TCP port 5060, aka Bug ID CSCso02147.
http://www.cisco.com/en/US/products/products_security_advisory09186a0080b95d4d.shtml
http://tools.cisco.com/security/center/viewAlert.x?alertId=24118