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CA-2003-09 Buffer Overflow in Microsoft IIS 5.0


CERT Advisory CA-2003-09 Buffer Overflow in Microsoft IIS 5.0

Original issue date: March 17, 2003
Last revised: --
Source: CERT/CC

A complete revision history is at the end of this file.

Systems Affected

* Systems running Microsoft Windows 2000 with IIS 5.0 enabled


A buffer overflow vulnerability exists in Microsoft IIS 5.0 running on
Microsoft Windows 2000. IIS 5.0 is installed and running by default on
Microsoft Windows 2000 systems. This vulnerability may allow a remote
attacker to run arbitrary code on the victim machine.

An exploit is publicly available for this vulnerability, which
increases the urgency that system administrators apply a patch.

I. Description

IIS 5.0 includes support for WebDAV, which allows users to manipulate
files stored on a web server (RFC2518). A buffer overflow
vulnerability exists in ntdll.dll (a portion of code utilized by the
IIS WebDAV component). By sending a specially crafted request to an
IIS 5.0 server, an attacker may be able to execute arbitrary code in
the Local System security context, essentially giving the attacker
compete control of the system.

Microsoft has issued the following bulletin regarding this
vulnerability: urity/bulletin/ms03-007.asp

This vulnerability has been assigned the identifier CAN-2003-0109 by
the Common Vulnerabilities and Exposures (CVE) group:

II. Impact

Any attacker who can reach a vulnerable web server can gain complete
control of the system and execute arbitrary code in the Local System
security context. Note that this may be significantly more serious
than a simple "web defacement."

III. Solution

Apply a patch from your vendor

A patch is available from Microsoft at

Disable vulnerable service

Until a patch can be applied, you may wish to disable IIS. To
determine if IIS is running, Microsoft recommends the following:

Go to Start | Settings | Control Panel | Administrative Tools | Services.

If the World Wide Web Publishing service is listed then IIS
is installed

To disable IIS, run the IIS lockdown tool. This tool is available

If you cannot disable IIS, consider using the IIS lockdown tool to
disable WebDAV (removing WebDAV can be specified when running the IIS
lockdown tool). Alternatively, you can disable WebDAV by following the
instructions located in Microsoft's Knowledgebase Article 241520, "How
to Disable WebDAV for IIS 5.0":;en-us;241520

Restrict buffer size

If you cannot use either IIS lockdown tool or URLScan, consider
restricting the size of the buffer IIS utilizes to process requests by
using Microsoft's URL Buffer Size Registry Tool. This tool can be run
against a local or remote Windows 2000 system running Windows 2000
Service Pack 2 or Service Pack 3. The tool, instructions on how to use
it, and instructions on how to manually make changes to the registry
are available here:

URL Buffer Size Registry Tool -

Microsoft Knowledge Base Article 816930 -;en-us;816930

Microsoft Knowledge Base Article 260694 -;en-us;260694

You may also wish to use URLScan, which will block web requests that
attempt to exploit this vulnerability. Information about URLScan is
available at:;[LN];326444

Appendix A. Vendor Information

This appendix contains information provided by vendors. When vendors
report new information, this section is updated and the changes are
noted in the revision history. If a vendor is not listed below, we
have not received their comments.

Microsoft Corporation

Please see Microsoft Security Bulletin MS03-007.

Author: Ian A. Finlay

This document is available from:

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Revision History

March 17, 2003: Initial release

Version: PGP 6.5.8


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