Unspecified vulnerability in Cisco IOS 12.0 through 12.4, when SIP voice services are enabled, allows remote attackers to cause a denial of service (device crash) via a valid SIP message.
https://exchange.xforce.ibmcloud.com/vulnerabilities/49421
http://www.vupen.com/english/advisories/2009/0851
http://www.securityfocus.com/bid/34243
http://www.cisco.com/en/US/products/products_security_advisory09186a0080a904c0.shtml
http://www.cisco.com/en/US/products/products_security_advisory09186a0080a90469.shtml