iDefense Security Advisory 02.12.08
http://labs.idefense.com/intelligence/vulnerabilities/
Feb 12, 2008

I. BACKGROUND

Clam AntiVirus is a multi-platform GPL anti-virus toolkit. ClamAV is
often integrated into e-mail gateways and used to scan e-mail traffic
for viruses. It supports virus scanning for a wide variety of packed
Portable Executable (PE) binaries. For more information visit the
vendor's web site 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 and
scanning PE files. While iterating through all sections contained in
the PE file, several attacker controlled values are extracted from the
file. On each iteration, arithmetic operations are performed without
taking into consideration 32-bit integer wrap.

Since insufficient integer overflow checks are present, an attacker can
cause a heap overflow by causing a specially crafted Petite packed PE
binary to be scanned. This results in an exploitable memory corruption
condition.

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.

Address Space Layout Randomization (ASLR) and non-executable memory
protection technologies (such as DEP, NX, XD, PaX, etc) can help
mitigate exploitation of this type of vulnerability.

IV. DETECTION

iDefense has confirmed the existence of this vulnerability in ClamAV
0.92. 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 0.92.1.
Additionally, the ClamAV team reports, "the vulnerable module was
remotely disabled via virus-db update on Jan 11th 2008."

VII. CVE INFORMATION

The Common Vulnerabilities and Exposures (CVE) project has assigned the
name CVE-2008-0318 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

01/07/2008  Initial vendor notification
01/11/2008  Initial vendor response
02/12/2008  Coordinated public disclosure

IX. CREDIT

This vulnerability was reported to iDefense by Silvio Cesare.

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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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