Cisco Catalyst 5000 series switches 6.1(2) and earlier will forward an 802.1x frame on a Spanning Tree Protocol (STP) blocked port, which causes a network storm and a denial of service.
https://exchange.xforce.ibmcloud.com/vulnerabilities/6379
http://www.securityfocus.com/bid/2604
http://www.cisco.com/warp/public/707/cat5k-8021x-vuln-pub.shtml