Internet Explorer 5.01, 5.5, and 6 allows remote attackers to spoof a less restrictive security zone and execute arbitrary code via an HTML page containing…

Internet Explorer 5.01, 5.5, and 6 allows remote attackers to spoof a less restrictive security zone and execute arbitrary code via an HTML page containing URLs that contain hostnames that have been double hex encoded, which are decoded twice to generate a malicious hostname, aka the "URL Decoding Zone Spoofing Vulnerability."