Public Vulnerability Reports

Microsoft Windows WMF Triggerable Kernel Design Error DoS Vulnerability

04.03.07

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/

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.

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.

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.

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.

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

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.

DISCLOSURE TIMELINE

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

CREDIT

This vulnerability was discovered by Greg MacManus of iDefense Labs.

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LEGAL NOTICES

Copyright © 2007 Verisign, 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. There are no warranties with regard to this information. Neither the author nor the publisher accepts any liability for any direct, indirect, or consequential loss or damage arising from use of, or reliance on, this information.