Public Vulnerability Reports

ClamAV libclamav MEW PE File Integer Overflow Vulnerability

12.18.07

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/

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.

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.

DETECTION

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

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'.

VENDOR RESPONSE

The ClamAV team has addressed this vulnerability within version 0.92.

CVE INFORMATION

The Common Vulnerabilities and Exposures (CVE) project has assigned the name CVE-2007-6335 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

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

CREDIT

The discoverer of this vulnerability wishes to remain anonymous.

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LEGAL NOTICES

Copyright © 2007 Verisign, 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.