iDefense Security Advisory 02.26.08
http://labs.idefense.com/intelligence/vulnerabilities/
Feb 26, 2008

I. BACKGROUND

Mozilla Thunderbird is an open source electronic mail client and news
reader. Multipurpose Internet Message Extensions (MIME) is a standard
that defines how non-text attachments and other data are handled in
electronic mail. The external-body MIME type is used for retrieving a
resource that is referenced in the message, such as an attachment. For
more information, see the vendor's website at the following URL.

http://www.mozilla.com/en-US/thunderbird/

II. DESCRIPTION

Remote exploitation of a heap based buffer overflow vulnerability in
Mozilla Organization's Thunderbird could allow an attacker to execute
arbitrary code with the privileges of the current user.

The vulnerability exists when parsing the external-body MIME type in an
electronic mail. When calculating the number of bytes to allocate for a
heap buffer, sufficient space is not reserved for all of the data being
copied into the buffer. This results in up to 3 bytes of the buffer
being overflowed, potentially allowing for the execution of arbitrary
code.

III. ANALYSIS

Exploitation of this vulnerability results in the execution of arbitrary
code with the privileges of the user running Thunderbird. Exploitation
requires that an attacker social engineers a user into viewing a
malicious message in Thunderbird. If the 'View->Message Pane' option is
turned on (the "Preview" pane), which is the default, then all a
targeted user has to do is select the message in the browsing pane.
Once the message is previewed, the vulnerability will be triggered.

IV. DETECTION

iDefense has confirmed the existence of this vulnerability in
Thunderbird version 2.0.0.9 on Linux and Windows. Previous versions may
also be affected.

V. WORKAROUND

Setting the "mailnews.display.disallow_mime_handlers" configuration
property to any value >= 3 will prevent the vulnerable code from being
triggered.

VI. VENDOR RESPONSE

The Mozilla Foundation has addressed this vulnerability by releasing
version 2.0.0.12 of Thunderbird. For more information, refer to their
advisory at the following URL.

http://www.mozilla.org/security/announce/2008/mfsa2008-12.html

VII. CVE INFORMATION

The Common Vulnerabilities and Exposures (CVE) project has assigned the
name CVE-2008-0304 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

01/14/2008  Initial vendor notification
01/14/2008  Initial vendor response
02/26/2008  Coordinated public disclosure

IX. CREDIT

This vulnerability was reported to VeriSign iDefense by regenrecht.

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X. LEGAL NOTICES

Copyright © 2008 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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