It's time to get the WebDAV out!

A buffer-overflow exploit has been discovered in a WebDAV component. The problem is that this component is installed and present by default on all IIS 5.0 systems (i.e. Windows 2000). The fault isn't directly with IIS; however, IIS is the channel most often used to gain access to the WebDAV component and exploit the vulnerability.

The attack is fairly simple. A specially formulated HTTP request to an IIS system can cause two effects. One effect is for the IIS system to simply crash. The other effect is for a buffer overflow to occur. The buffer overflow results in the IIS system executing code of the attacker's choice. The overflow code is executed with the security privileges of the IIS service (i.e. the LocalSystem account). This is what I like to call a very bad thing.

Fortunately, this problem is very easy to address. Unfortunately, too many systems are still unpatched or unprotected. Microsoft has a patch specifically for this issue. If you are using WebDAV and it is essential to your business operations, get the patch and install it. If you do not need WebDAV, I think it is safer to get rid of it than to patch it.

WebDAV can be disabled with a quick Registry edit, if you have applied the Security Rollup Package 1 (SRP1) from January of 2002. The details of this action are contained at http://support.microsoft.com/default.aspx?scid=kb;en-us;241520.

Use of the IIS Lockdown tool or URLScan can both inhibit access to WebDAV's vulnerability through controlling submitted URLs. However, it is always important to check that your system is patched and protected. Don't just assume that because you have these tools residing on your hard drive or you remember running them once that your system is safe.

For access to the patch and for other details on this problem, see MS03-007 at http://www.microsoft.com/technet/treeview/default.asp?url=/technet/security/bulletin/ms03-007.asp.

About the author
James Michael Stewart is a partner and researcher for ITinfopros, a technology-focused writing and training organization.

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This was first published in April 2003

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