The SSL VPN (aka WebVPN) feature in Cisco IOS 15.1 through 15.4 allows remote attackers to cause a denial of service (memory consumption) via crafted HTTP requests, aka Bug ID CSCuf51357.
http://www.securityfocus.com/bid/66462
http://tools.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-20140326-ios-sslvpn