iDefense Security Advisory 12.18.07
http://labs.idefense.com/intelligence/vulnerabilities/
Dec 18, 2007

I. BACKGROUND

Clam AntiVirus is a multi-platform anti-virus toolkit released under the
GNU Public License. ClamAV is often integrated into e-mail gateways and
used to scan e-mail messages for viruses. PE, or portable executable,
is the executable file format on Microsoft Windows systems. MEW is one
of the many executable packers that is supported by ClamAV. More
information can be found on the vendor's website at the following URL.

http://www.clamav.net/

II. DESCRIPTION

Remote exploitation of an integer overflow vulnerability in Clam
AntiVirus' ClamAV, as included in various vendors' operating system
distributions, allows attackers to execute arbitrary code with the
privileges of the affected process.

The vulnerability exists within the code responsible for parsing PE
files packed with the MEW packer. During unpacking, two untrusted
values are taken directly from the file without being validated. These
values are later used in an arithmetic operation to calculate the size
used to allocate a heap buffer. This calculation can overflow,
resulting in a buffer of insufficient size being allocated. This later
leads to arbitrary areas of memory being overwritten with attacker
supplied data.

III. ANALYSIS

Exploitation of this vulnerability results in the execution of arbitrary
code with the privileges of the process using libclamav.

In the case of the clamd program, this will result in code execution
with the privileges of the clamav user. Unsuccessful exploitation
results in the clamd process crashing.

IV. DETECTION

iDefense has confirmed the existence of this vulnerability in ClamAV
0.91.2. Previous versions may also be affected.

V. WORKAROUND

Disabling the scanning of PE files will prevent exploitation. If using
clamscan, this can be done by running clamscan with the '--no-pe'
option. If using clamdscan, set the 'ScanPE' option in the clamd.conf
file to 'no'.

VI. VENDOR RESPONSE

The ClamAV team has addressed this vulnerability within version 0.92.

VII. CVE INFORMATION

The Common Vulnerabilities and Exposures (CVE) project has assigned the
name CVE-2007-5759 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

10/17/2007  Initial vendor notification
10/18/2007  Initial vendor response
12/18/2007  Coordinated public disclosure

IX. CREDIT

The discoverer of this vulnerability wishes to remain anonymous.

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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.
 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.