iDefense Security Advisory 02.15.07: Multiple Vendor ClamAV MIME Parsing Directory Traversal Vulnerability

Multiple Vendor ClamAV MIME Parsing Directory Traversal Vulnerability

iDefense Security Advisory 02.15.07
http://labs.idefense.com/intelligence/vulnerabilities/
Feb 15, 2007

I. BACKGROUND

Clam AntiVirus is a multi-platform GPL anti-virus toolkit. ClamAV is often
integrated into mail gateways, and used to scan mail traffic for viruses.
More information about ClamAV is available from http://clamav.net/.
Multipurpose Internet Mail Extensions (MIME), is an internet standard for
sending email with non-text attachments, multi-part message bodies, and
non-ASCII character sets.

II. DESCRIPTION

Remote exploitation of a directory traversal vulnerability in Clam
AntiVirus' ClamAV allows attackers to overwrite files owned by the clamd
scanner.

The vulnerability specifically exists due to the lack of validation of the
id parameter string taken from a MIME header. When parsing a multi-part
message clam takes this string from the header and uses it to create a
local file. By sending a string such as "…/…/…/…/some/file" an
attacker can create or overwrite an arbitrary file owned by the clamd
process. Data from the message body is later written to this file.

III. ANALYSIS

Exploitation allows attackers to degrade the service of the ClamAV virus
scanning service. The most important mitigating factor is that the clam
process runs with the privileges of the clamav user and group. This group
has access to a limited subset of files on the host. A possible target for
overwriting is the virus database file. By overwriting this file an
attacker could then send a virus through the gateway without clam
recognizing it; this effectively denies service. Arbitrary viruses will be
allowed to pass through, creating a false sense of security.

IV. DETECTION

iDefense has confirmed this vulnerability affects Clam AntiVirus ClamAV
v0.88.6. All versions prior to the 0.90 stable release are suspected to be
vulnerable.

V. WORKAROUND

iDefense is unaware of any effective workarounds for this issue.

VI. VENDOR RESPONSE

Clam AntiVirus has addressed this vulnerability in the version 0.90 stable
release.

VII. CVE INFORMATION

The Common Vulnerabilities and Exposures (CVE) project has assigned the
name CVE-2007-0898 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

02/07/2007 Initial vendor notification
02/13/2007 Initial vendor response
02/15/2007 Coordinated public disclosure

IX. CREDIT

The discoverer of this vulnerability wishes to remain anonymous.

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X. LEGAL NOTICES

Copyright © 2006 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.