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Microsoft Windows Mail and Outlook Express NNTP Protocol Heap Overflow

10.09.07

BACKGROUND

Microsoft Windows Mail and Outlook Express are the default mail and news clients for Windows operating systems. More information can be found at the following URLs.

http://www.microsoft.com/windows/products/windowsvista/features/details/mail.mspx
http://www.microsoft.com/windows/ie/ie6/using/oe/default.mspx

DESCRIPTION

Remote exploitation of a heap overflow in Microsoft Corp.'s Windows Mail and Outlook Express NNTP clients may allow an attacker to execute code with the privileges of the logged on user.

NNTP (Network News Transfer Protocol) is a protocol for reading and posting Usenet articles. Windows Mail and Outlook Express both contain a heap overflow vulnerability in their handling of NNTP replies. If the server returns more data than the client requests, attacker controlled values can be stored outside of the allocated memory region, overwriting control structures in a way which may allow code execution.

ANALYSIS

Exploitation of this vulnerability would allow an attacker to execute arbitrary code in the context of the currently logged on user. In order to exploit this vulnerability, and attacker would need to convince the targeted user to view a website under their control or otherwise open a link to their NNTP server. No further interaction is required to exploit the vulnerability.

If the 'nntp', 'news' or 'snews' (secure news) protocol handlers have not been explicitly associated with another application, the default handlers will be set to Windows Mail (in Vista) and Outlook Express (in previous versions of Windows). Exploitation of this vulnerability does not require the targeted user to have setup an account in the affected program.

DETECTION

iDefense confirmed the following programs on Windows operating systems are affected:

 Windows Mail on Windows Vista Outlook Express 6 on Windows XP SP2 Outlook Express 6 on Windows 2000 SP4 

WORKAROUND

Deleting the all sub-keys of the following registry keys will remove the 'news' and 'snews' protocol handlers:

 HKEY_CLASSES_ROOTnewsshell HKEY_CLASSES_ROOTsnewsshell 

These keys may be restored under some circumstances. To prevent this from occurring, Set the 'Deny Full Control' permission for the group 'Everyone' on the keys.

VENDOR RESPONSE

Microsoft has addressed this vulnerability within MS07-056. For more information, consult their bulletin at the following URL.

http://www.microsoft.com/technet/security/Bulletin/MS07-056.mspx

CVE INFORMATION

The Common Vulnerabilities and Exposures (CVE) project has assigned the name CVE-2007-3897 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

07/11/2007 Initial vendor notification
07/11/2007 Initial vendor response
10/09/2007 Coordinated public disclosure

CREDIT

This vulnerability was discovered by Greg MacManus of VeriSign iDefense Labs.

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LEGAL NOTICES

Copyright © 2007 Verisign, Inc.

Permission is granted for the redistribution of this alert electronically. It may not be edited in any way without the express written consent of iDefense. If you wish to reprint the whole or any part of this alert in any other medium other than electronically, please e-mail customer service for permission.

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.