iDefense Security Advisory 04.14.08 http://labs.idefense.com/intelligence/vulnerabilities/ Apr 14, 2008 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. 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/ II. 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. III. 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. IV. DETECTION iDefense has confirmed the existence of this vulnerability in ClamAV 0.92.1. Previous versions may also be affected. V. 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'. VI. VENDOR RESPONSE VII. CVE INFORMATION A Mitre Corp. Common Vulnerabilities and Exposures (CVE) number has not been assigned yet. VIII. DISCLOSURE TIMELINE 03/04/2008 Initial vendor notification 03/06/2008 Initial vendor response 04/14/2008 Coordinated public disclosure IX. CREDIT This vulnerability was reported to iDefense by Damian Put and Thomas Pollet. Get paid for vulnerability research http://labs.idefense.com/methodology/vulnerability/vcp.php Free tools, research and upcoming events http://labs.idefense.com/ X. LEGAL NOTICES Copyright © 2008 iDefense, Inc. Permission is granted for the redistribution of this alert electronically. It may not be edited in any way without the express written consent of iDefense. If you wish to reprint the whole or any part of this alert in any other medium other than electronically, please e-mail customerservice@idefense.com for permission. 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.