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Microsoft IIS Authentication Method Disclosure Vulnerability
by Nikola Strahija on March 7th, 2002 Microsoft IIS supports Basic and NTLM authentication. It has been reported that the authentication methods supported by a given IIS server can be revealed to an attacker through the inspection of returned error messages, even when anonymous access is also granted.
When a valid authentication request is submitted for either message with an invalid username and password, an error message will be returned. This happens even if anonymous access to the requested resource is allowed. An attacker may be able to use this information to launch further intelligent attacks against the server, or to launch a brute force password attack against a known user name.
Remote: Yes
Exploit: No exploit is required. The following HTTP requests have been provided as examples by David Litchfield ([email protected]):
GET / HTTP/1.1
Host: iis-server
Authorization: Basic cTFraTk6ZDA5a2xt
GET / HTTP/1.1
Host: iis-server
Authorization: Negotiate TlRMTVNTUAABAAAAB4IAoAAAAAAAAAAAAAAAAAAAAAA=
