Cisco Gigabit Switch Routers (GSR) with Fast Ethernet / Gigabit Ethernet cards, from IOS versions 11.2(15)GS1A up to 11.2(19)GS0.2 and some versions of 12.0, do not properly handle line card failures, which allows remote attackers to bypass ACLs or force the interface to stop forwarding packets.
http://www.securityfocus.com/bid/1541
http://www.cisco.com/warp/public/707/gsraclbypassdos-pub.shtml