Microsoft Windows WMF Triggerable Kernel Design Error DoS Vulnerability

iDefense Security Advisory 04.03.07
http://labs.idefense.com/intelligence/vulnerabilities/
Apr 03, 2007

I. BACKGROUND

The Microsoft Windows kernel controls which processes are allowed to run
and is responsible for accessing hardware such as storage devices and
video adapters, scheduling time for each process to execute, managing
memory, and other system control tasks. For more information on on the
Windows kernel visit MSDN at the URL shown below.

http://msdn.microsoft.com/

II. DESCRIPTION

Remote exploitation of a design error in certain kernel GDI functions in
multiple versions of Microsoft Corp.'s Windows operating system may
allow an attacker to cause a denial of service condition.

During testing of the MS06-001 WMF (Windows Metafile) vulnerability, a
flaw was found in the handling of WMF files. This flaw can cause the
kernel to perform a bug check, also known as a "blue screen" or system
crash, when it tries to parse the file. The cause of this bug check is
an attempt by a function in a kernel system call to read a value
obtained by dereferencing an offset into a kernel structure. This value
had been previously created and then reset by previous system calls, and
at the point it is accessed it does not contain a valid memory
reference. This results in an access violation error, which in turn
triggers the bug check.

This vulnerability is different from both the Microsoft MS06-001 WMF
vulnerability and the MS05-053 WMF vulnerability and is not fixed by
either of these patches.

III. ANALYSIS

Exploitation of this vulnerability would allow a remote attacker to
perform a denial of service against an affected system.

Depending on where the file was saved and configuration details of the
target, this could result in a persistent denial of service condition,
causing an immediate reboot upon logging on after an attack. The
results of testing this vulnerability suggest that in some cases it may
cause corruption of the system in a manner that prevents the system from
rebooting.

It is likely that Enhanced Windows Metafiles (EMF) are also affected,
but this has not yet been confirmed.

Currently, due to the type of location being referenced by the kernel,
it appears that the vulnerability may only be exploitable by a remote
attacker to cause a DoS condition. The vectors that could be used to
remotely exploit this vulnerability would most likely be similar to
those that the MS06-001 vulnerability used.

IV. DETECTION

This vulnerability has been confirmed to affect the following Microsoft
Windows operating systems:

  * Windows XP with Service Pack 2
  * Windows 2003 Server

Other Windows operating systems may also be affected.

V. WORKAROUND

Blocking .wmf files at all e-mail and Web gateways is strongly
recommended. However, this is not effective if blocking is done based
on file extensions (e.g., .wmf), as an attacker can simply rename the
file to a new extension.

Reading e-mail in plain-text can prevent automatic exploitation via
electronic mail.

VI. VENDOR RESPONSE

Microsoft has addressed this vulnerability within MS07-017. For more
information, consult their bulletin at the following URL.

http://www.microsoft.com/technet/security/Bulletin/MS07-017.mspx

VII. CVE INFORMATION

The Common Vulnerabilities and Exposures (CVE) project has assigned the
name CVE-2007-1211 to this issue. This is a candidate for inclusion in
the CVE list (http://cve.mitre.org/), which standardizes names for
security problems.

VIII. DISCLOSURE TIMELINE

01/10/2006  Initial vendor notification
01/10/2006  Initial vendor response
04/03/2007  Coordinated public disclosure

IX. CREDIT

This vulnerability was discovered by Greg MacManus of iDefense Labs.

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X. LEGAL NOTICES

Copyright © 2007 iDefense, Inc.

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Disclaimer: The information in the advisory is believed to be accurate
at the time of publishing based on currently available information. Use
of the information constitutes acceptance for use in an AS IS condition.
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