Cisco 12000 with IOS 12.0 and line cards based on Engine 2 and earlier allows remote attackers to cause a denial of service (CPU consumption) by flooding the router with traffic that generates a large number of ICMP Unreachable replies.
https://exchange.xforce.ibmcloud.com/vulnerabilities/7536
http://www.securityfocus.com/bid/3534
http://www.cisco.com/warp/public/707/GSR-unreachables-pub.shtml