Memory leak in Cisco Catalyst 4000, 5000, and 6000 series switches allows remote attackers to cause a denial of service via a series of failed telnet authentication attempts.
https://exchange.xforce.ibmcloud.com/vulnerabilities/5656
http://www.securityfocus.com/bid/2072
http://www.cisco.com/warp/public/707/catalyst-memleak-pub.shtml