Microsoft IIS Malformed Filename Security Bypass Vulnerability

Microsoft IIS is prone to a security-bypass vulnerability. This vulnerability may result in IIS interpreting unexpected files as CGI applications. Attackers may be able to exploit this vulnerability to bypass intended security restrictions. Microsoft Internet Information Services (IIS) 5.x and 6.x uses only the portion of a filename before a ; (semicolon) character to determine the file extension, which allows remote attackers to bypass intended extension restrictions of third-party upload applications via a filename with a (1) .asp, (2) .cer, or (3) .asa first extension, followed by a semicolon and a safe extension, as demonstrated by the use of asp.dll to handle a .asp;.jpg file.