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Multiple Vendor ClamAV MIME Parsing Directory Traversal Vulnerability

02.15.07

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.

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.

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.

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.

WORKAROUND

iDefense is unaware of any effective workarounds for this issue.

VENDOR RESPONSE

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

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.

DISCLOSURE TIMELINE

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

CREDIT

The discoverer of this vulnerability wishes to remain anonymous.

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LEGAL NOTICES

Copyright © 2006 Verisign, Inc.

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