The provider-edge MPLS 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) via a malformed SIP packet to UDP port 5060, aka Bug ID CSCti98219.
https://oval.cisecurity.org/repository/search/definition/oval%3Aorg.mitre.oval%3Adef%3A13781
http://www.cisco.com/en/US/products/products_security_advisory09186a0080b95d4d.shtml
http://tools.cisco.com/security/center/viewAlert.x?alertId=24121