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

From: iDEFENSE Labs (labs-no-reply_at_idefense.com)
Date: 06/29/05

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    Date: Wed, 29 Jun 2005 10:49:13 -0400
    To: <bugtraq@securityfocus.com>, <vulnwatch@vulnwatch.org>, <full-disclosure@lists.grok.org.uk>
    
    

    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.


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