Race condition in the Firewall Authentication Proxy feature in Cisco IOS 12.0 through 12.4 allows remote attackers to bypass authentication, or bypass the consent web page, via a crafted request, aka Bug ID CSCsy15227.
https://exchange.xforce.ibmcloud.com/vulnerabilities/53453
http://www.securitytracker.com/id?1022935
http://www.securityfocus.com/bid/36491
http://www.cisco.com/en/US/products/products_security_advisory09186a0080af8132.shtml
http://tools.cisco.com/security/center/viewAlert.x?alertId=18882