Microsoft Windows Mail and Outlook Express NNTP Protocol Heap Overflow

iDefense Security Advisory 10.09.07
https://labs.idefense.com/intelligence/vulnerabilities/
Oct 09, 2007

I. 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.

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

II. 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.

III. 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.

IV. 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

V. WORKAROUND

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

  HKEY_CLASSES_ROOT\news\shell
  HKEY_CLASSES_ROOT\snews\shell

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.

VI. VENDOR RESPONSE

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

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

VII. 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 (https://cve.mitre.org/), which standardizes names for
security problems.

VIII. DISCLOSURE TIMELINE

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

IX. CREDIT

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

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X. LEGAL NOTICES

Copyright © 2007 iDefense, Inc.

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at the time of publishing based on currently available information. Use
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