Internet Explorer 5.01 through 6.0 does not properly perform security checks on certain encoded characters within a URL, which allows a remote attacker to steal potentially sensitive information from a user by redirecting the user to another site that has that information, aka "Encoded Characters Information Disclosure."
https://oval.cisecurity.org/repository/search/definition/oval%3Aorg.mitre.oval%3Adef%3A495
https://oval.cisecurity.org/repository/search/definition/oval%3Aorg.mitre.oval%3Adef%3A471
https://oval.cisecurity.org/repository/search/definition/oval%3Aorg.mitre.oval%3Adef%3A143
https://docs.microsoft.com/en-us/security-updates/securitybulletins/2002/ms02-066
http://www.securityfocus.com/bid/5610
http://www.iss.net/security_center/static/10039.php
http://archives.neohapsis.com/archives/bugtraq/2002-09/0030.html