WebVPN on the Cisco Adaptive Security Appliances (ASA) device with software 8.0(4), 8.1.2, and 8.2.1 allows remote attackers to bypass certain protection mechanisms involving URL rewriting and HTML rewriting, and conduct cross-site scripting (XSS) attacks, by modifying the first hex-encoded character in a /+CSCO+ URI, aka Bug ID CSCsy80705.