Unspecified vulnerability in the NAT for SIP implementation in Cisco IOS 12.1 through 12.4 and 15.0 through 15.1 allows remote attackers to cause a denial of service (device reload) via transit traffic on UDP port 5060, aka Bug ID CSCtf17624.
http://www.cisco.com/en/US/products/products_security_advisory09186a0080b4a311.shtml