Cisco IOS 11.1 through 12.2, when HSRP support is not enabled, allows remote attackers to cause a denial of service (CPU consumption) via randomly sized UDP packets to the Hot Standby Routing Protocol (HSRP) port 1985.
https://exchange.xforce.ibmcloud.com/vulnerabilities/9282
http://www.securityfocus.com/bid/4948
http://archives.neohapsis.com/archives/bugtraq/2002-06/0050.html
http://archives.neohapsis.com/archives/bugtraq/2002-06/0027.html