Microsoft falters again !

A new vulnerability has been discovered in Microsoft IIS 6.0 which allows an attacker to access protected(password) content in a website. The vulnerability arises because of the way IIS handles Unicode.

Microsoft has released a security advisory 971492 and it’s follow-up

According to the advisory the scale of vulnerable systems is reduced due to multiple factors

* An IIS server not running WebDAV is safe.
The Windows Server 2003 IIS (version 6) shipped with WebDAV disabled by default.
* An IIS server not using IIS permissions to restrict content to authenticated users is safe.
* An IIS server that does not grant filesystem access to the IUSR_[MachineName] account is safe.
* An IIS server that hosts web applications using only forms-based authentication is probably safe.

If your web server meets all of the following criteria, you will want to read on:

* IF an IIS 5, 5.1, or 6.0 webserver is running with WebDAV enabled;
* AND the IIS server is using IIS permissions to restrict a subfolder of content to authenticated users;
* AND file system access is granted for the restricted content to the IUSR_[MachineName] account;
* AND a parent folder of the private subfolder allows anonymous access;
THEN an anonymous remote user may be able to leverage this vulnerability to access files that normally would only be served to authenticated webserver users.

This vulnerability is primarily an information disclosure threat.

Thierry Zoller has made an excellent post explaining the vulnerability with graphical representation. It’s a must-read.

He made a reference to the SANS article on the original Unicode vulnerability in IIS 4.0 and 5.0 which explains the Unicode issues in depth.

There are a few tools that can be used to search for WebDav enabled servers on the network (referenced from Zoller’s blog
* Specifically for this vulnerability: Metasploit added test script to the trunk (use svn update to get the latest exploits)
* Webdav network scanner here
* Nmap webdav scanner

Till Microsoft releases a patch to fix this vulnerability, it’s best to disable WebDAV on IIS servers (Sharepoint user beware)