Cisco IOS after 12.3(14)T, 12.3(8)YC1, 12.3(8)YG, and 12.4, with voice support and without Session Initiated Protocol (SIP) configured, allows remote attackers to cause a denial of service (crash) by sending a crafted packet to port 5060/UDP.
https://oval.cisecurity.org/repository/search/definition/oval%3Aorg.mitre.oval%3Adef%3A5138
https://exchange.xforce.ibmcloud.com/vulnerabilities/31990
http://www.vupen.com/english/advisories/2007/0428
http://www.securityfocus.com/bid/22330
http://www.kb.cert.org/vuls/id/438176
http://www.cisco.com/warp/public/707/cisco-sa-20070131-sip.shtml
http://www.cisco.com/warp/public/707/cisco-air-20070131-sip.shtml