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. Get paid for vulnerability research http://labs.idefense.com/methodology/vulnerability/vcp.php Free tools, research and upcoming events http://labs.idefense.com/ X. LEGAL NOTICES Copyright © 2007 iDefense, Inc. Permission is granted for the redistribution of this alert electronically. It may not be edited in any way without the express written consent of iDefense. If you wish to reprint the whole or any part of this alert in any other medium other than electronically, please e-mail customerservice@private for permission. 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.
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