The "hit-highlighting" functionality in webhits.dll in Microsoft Internet Information Services (IIS) Web Server 5.0 only uses Windows NT ACL configuration, which allows remote attackers to bypass NTLM and basic authentication mechanisms and access private web directories via the CiWebhitsfile parameter to null.htw.
http://www.securityfocus.com/bid/24105
http://www.securityfocus.com/archive/1/469238/100/0/threaded
http://support.microsoft.com/kb/328832