Public Vulnerability Reports

ClamAV libclamav PE WWPack Heap Overflow Vulnerability

14.04.08

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. It supports virus scanning for a wide variety of packed Portable Executable (PE) binaries. WWPack is one of the supported packers. For more information visit the vendor's web site at the following URL.

http://www.clamav.net/

DESCRIPTION

Remote exploitation of a heap 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 reading in sections within a PE binary packed with the WWPack executable compressor. See the following excerpt from libclamav/pe.c:

 1879 dsize = max-min+headsize-exe_sections[nsections - 1].rsz; .... 1883 if((dest = (char *) cli_calloc(dsize, sizeof(char))) == NULL) { .... 1897 for(i = 0 ; i < (unsigned int)nsections-1; i++) { 1898 if(exe_sections[i].rsz) { 1899 if(!cli_seeksect(desc, &exe_sections[i]) || (unsigned int) cli_readn(desc, dest + headsize + exe_sections[i].rva - min, exe_sections[i].rsz) != exe_sections[i].rsz) { 

The size of the allocated heap buffer is calculated on line 1879 using several values that are under attacker control. The allocation takes place on line 1883. Within the loop, starting on line 1897, data is read into the allocated buffer (line 1899).

No validation is done to ensure that the resulting data is not written outside the bounds of the "dest" buffer. The "headsize", "exe_sections[i].rva", "min", and "exe_sections[i].rsz" values that are used for this operation are all under attacker control. As such, an exploitable heap corruption condition may occur.

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.

DETECTION

iDefense has confirmed the existence of this vulnerability in ClamAV 0.92.1. Previous versions may also be affected.

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'. 

VENDOR RESPONSE

The ClamAV team has addressed this vulnerability within version 0.93. Additionally, the ClamAV team reports, "the vulnerable module was remotely disabled via virus-db update in March."

CVE INFORMATION

The Common Vulnerabilities and Exposures (CVE) project has assigned the name CVE-2008-1833 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

03/04/2008 Initial vendor notification
03/06/2008 Initial vendor response
04/14/2008 Coordinated public disclosure

CREDIT

This vulnerability was reported to iDefense by Damian Put and Thomas Pollet.

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LEGAL NOTICES

Copyright © 2008 Verisign, Inc.

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