A vulnerability in Web Authentication (WebAuth) clients for the Cisco Wireless LAN Controller (WLC) and Aironet Access Points running Cisco IOS Software could allow an unauthenticated, adjacent attacker to bypass authentication and pass traffic. The vulnerability is due to incorrect implementation of authentication for WebAuth clients in a specific configuration. An attacker could exploit this vulnerability by sending traffic to local network resources without having gone through authentication. A successful exploit could allow the attacker to bypass authentication and pass traffic. This affects Cisco Aironet Access Points running Cisco IOS Software and Cisco Wireless LAN Controller (WLC) releases prior to 8.5.110.0 for the following specific WLC configuration only: (1) The Access Point (AP) is configured in FlexConnect Mode with NAT. (2) The WLAN is configured for central switching, meaning the client is being assigned a unique IP address. (3) The AP is configured with a Split Tunnel access control list (ACL) for access to local network resources, meaning the AP is doing the NAT on the connection. (4) The client is using WebAuth. This vulnerability does not apply to .1x clients in the same configuration. Cisco Bug IDs: CSCvc79502, CSCvf71789.