Clam AntiVirus ClamAV CAB File Unstore Buffer Overflow Vulnerability

iDefense Security Advisory 04.16.07
http://labs.idefense.com/intelligence/vulnerabilities/
Apr 16, 2007

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. Cabinet, or CAB, files are the Microsoft Windows native
format for storing compressed archives. More information can be found
on the vendor's website at the following URL.

http://www.clamav.net/

II. DESCRIPTION

Remote exploitation of a buffer overflow vulnerability in Clam
AntiVirus' ClamAV allows attackers to execute arbitrary code with the
privileges of the affected process.

The vulnerability exists within the cab_unstore() function in libclamav,
the library used by clamd to scan various file types. A 32-bit signed
integer is taken from the packet and compared against the sizeof() the
destination buffer. However, the sizeof() return value is improperly
casted to a signed integer. By supplying a negative value, an attacker
can pass cause the comparison to succed. This eventually leads to an
exploitable stack-based buffer overflow.

III. ANALYSIS

Successful exploitation of this vulnerability results in code execution
with the privileges of the process using libclamav.

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

This vulnerability only exists in the recent 0.9x versions of ClamAV. As
such, the vulnerable code is not present in the versions distributed
with Red Hat Enterprise or other open source distributions.

IV. DETECTION

iDefense has confirmed the existence of this vulnerability in ClamAV in
versions 0.90rc3 through 0.90.1.

V. WORKAROUND

iDefense is currently unaware of any workaround for this issue.

VI. VENDOR RESPONSE

The ClamAV team has addressed this vulnerability within version 0.90.2.

VII. CVE INFORMATION

The Common Vulnerabilities and Exposures (CVE) project has assigned the
name CVE-2007-1997 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

04/05/2007  Initial vendor notification
04/06/2007  Initial vendor response
04/16/2007  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
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