iDEFENSE Security Advisory 06.29.05: Clam AntiVirus ClamAV MS-Expand File Handling DoS Vulnerability

2005-06-30T00:00:00
ID SECURITYVULNS:DOC:9002
Type securityvulns
Reporter Securityvulns
Modified 2005-06-30T00:00:00

Description

Clam AntiVirus ClamAV MS-Expand File Handling DoS Vulnerability

iDEFENSE Security Advisory 06.29.05 www.idefense.com/application/poi/display?id=276&type=vulnerabilities June 29, 2005

I. BACKGROUND

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

II. DESCRIPTION

Remote exploitation of an input validation error in Clam AntiVirus ClamAV allows attackers to cause a denial of service condition.

The vulnerability specifically exists due to improper behavior during exceptional conditions. The following piece of code from libclamav/scanners.c shows where the vulnerability exists:

static int cli_scanszdd(...)
{
  [...]
  FILE *tmp = NULL, *in;

  cli_dbgmsg("in cli_scanmscomp()\n");

  if((in = fdopen(dup(desc), "rb")) == NULL) {
    cli_dbgmsg("SZDD: Can't open descriptor %d\n", desc);
    return CL_EMSCOMP;
  }

  if((tmp = tmpfile()) == NULL) {
    cli_dbgmsg("SZDD: Can't generate temporary file.\n");
    fclose(in);
    return CL_ETMPFILE;
  }

  if(cli_msexpand(in, tmp) == -1) {
    cli_dbgmsg("SZDD: msexpand failed.\n");
    return CL_EMSCOMP;
  }

  [...]
}

Each time the cli_msexpand() function fails , two file descriptors ('in'

and 'tmp') are leaked. As they are both opened using fopen(), there is also a memory leak (2 * 364 bytes). This allows an attacker to exhaust all of the available file descriptors fairly quickly with around 1,000 malformed files.

III. ANALYSIS

Successful exploitation allows attackers to exhaust file descriptors pool and memory. Anti-virus detection functionality will fail if there is no file descriptors available with which to open files. Remote exploitation can be achieved by sending a malicious file in an e-mail message or during an HTTP session.

IV. DETECTION

iDEFENSE has confirmed the existence of this vulnerability in ClamAV 0.83. It is suspected that all versions of ClamAV prior to 0.86 are vulnerable.

The following vendors distribute susceptible ClamAV packages within their respective operating system distributions:

    FreeBSD Project: FreeBSD 5.4 and prior
    Gentoo Foundation Inc.: Gentoo Linux 1.1a, 1.2, 1.4, 2004.0,

2004.1 and 2004.2 Mandrakesoft SA: Mandrakelinux 10.1 and Corporate Server 3.0 Novell Inc.: SuSE Linux 9.1, 9.2

V. WORKAROUND

As a temporary workaround solution, scanning of archive files can be disabled by supplying the --no-archive flag; however, this will significantly impact the effectiveness of the AV engine.

VI. VENDOR RESPONSE

This vulnerability has been patched in clamav 0.86 which is available for download at:

http://www.clamav.net/stable.php#pagestart

VII. CVE INFORMATION

The Common Vulnerabilities and Exposures (CVE) project has assigned the name CAN-2005-1922 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

06/07/2005 Initial vendor notification 06/08/2005 Initial vendor response 06/29/2005 Public disclosure

IX. CREDIT

The discoverer of this vulnerability wishes to remain anonymous.

Get paid for vulnerability research http://www.idefense.com/poi/teams/vcp.jsp

Free tools, research and upcoming events http://labs.idefense.com

X. LEGAL NOTICES

Copyright (c) 2005 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 email 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.