Clam AntiVirus DoS Vulnerability & Remote code execution

dropby23

Well-Known Member
Jan 16, 2005
155
0
166
nfo on the DoS:
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Clam AntiVirus tnef_attachment() DoS Vulnerability

iDEFENSE Security Advisory 11.04.05
http://www.idefense.com/application/poi/display?type=vulnerabilities
November 4, 2005

I. BACKGROUND

Clam AntiVirus is a GPL anti-virus toolkit for Unix.

II. DESCRIPTION

Remote exploitation of a design error in Clam AntiVirus ClamAV allows attackers to cause a denial of service (DoS) condition.

The vulnerability specifically exists in the tnef_attachment function within tnef.c. A user controlled value is used to fseek into the file that is being processed; this allows a user to specify the same block for scanning repeatedly, thus leading to an infinite loop. The following one line code snippet from the tnef processor demonstrates the flaw:

fseek(fp, (long)(offset + length), SEEK_SET); /* shouldn't be needed */


When this code is reached, length is supplied by the file being processed. This makes it possible to seek back to the previous header, causing the infinite loop to begin. Furthermore, if the block is marked as an attachment, the data that is repeatedly read will be added to a dynamically allocated memory buffer, making memory exhaustion trivial.

III. ANALYSIS

Successful exploitation requires an attacker to send a specially constructed CAB file through a mail gateway or personal anti-virus client utilizing the ClamAV scanning engine.

The infinite loop will cause the ClamAV software to use all available processor resources, resulting in a DoS or severe degradation of system performance. Ultimately, the OOM handler will terminate a task to alleviate the stress on the system.

IV. DETECTION

iDEFENSE has confirmed this vulnerability on ClamAV 0.86.1. All previous versions are suspected vulnerable to this issue.

V. WORKAROUND

Archive file analysis can be disabled (--no-archive) but this can have severe impacts on the virus detection functionality.

VI. VENDOR RESPONSE

The vendor has released clamav 0.87.1 to address this vulnerability. It is available for download at:

http://prdownloads.sourceforge.net/clamav/clamav-0.87.1.tar.gz?download
VII. CVE INFORMATION

A Mitre Corp. Common Vulnerabilities and Exposures (CVE) number has not been assigned yet.

VIII. DISCLOSURE TIMELINE

10/07/2005 Initial vendor notification
10/12/2005 Initial vendor response
11/04/2005 Coordinated public disclosure
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Info on the Remote Code Execution

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-- Vulnerability Details:
This vulnerability allows remote attackers to execute arbitrary code on vulnerable ClamAV installations. Authentication is not required to exploit this vulnerability.

This specific flaw exists within libclamav/fsg.c during the unpacking of executable files compressed with FSG v1.33. Due to invalid bounds checking when copying user-supplied data to heap allocated memory, an exploitable memory corruption condition is created. The unpacking algorithm for other versions of FSG is not affected.

-- Vendor Response:
The bug has been fixed in version 0.87.1. Release notes:
http://www.sourceforge.net/project/shownotes.php?release_id=368319
- Disclosure Timeline:
2005.10.24 - Vulnerability reported to vendor
2005.10.24 - Digital Vaccine released to TippingPoint customers
2005.10.25 - Vulnerability information provided to ZDI security partners
2005.11.04 - Public release of advisory
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vote for this
http://bugzilla.cpanel.net/show_bug.cgi?id=3471
 

lbccserv

Active Member
Mar 23, 2004
38
0
156
cpanel

Is the cpanel version upgraded? My clamav failed this morning for the first time ever