[Full-disclosure] iDEFENSE Security Advisory 11.04.05: Clam AntiVirus Cabinet-file handling Denial of Service Vulnerability

From: iDEFENSE Labs (labs-no-reply_at_idefense.com)
Date: 11/05/05

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    Date: Fri, 4 Nov 2005 18:16:13 -0500
    To: <bugtraq@securityfocus.com>, <vulnwatch@vulnwatch.org>, <full-disclosure@lists.grok.org.uk>
    
    

    Clam AntiVirus Cabinet-file handling Denial of Service 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 with the libmspack library, which
    is included in ClamAV. The vulnerability can be found in the cabd_find
    function within mspack/cabd.c:

    for (offset = 0; offset < flen; offset += length) {
        length = flen - offset;

        [... read length from file ...]

        for (p = &buf[0], pend = &buf[length]; p < pend; ) {
          switch (state) {
            [ ... ]
            case 19:
    => header has been completely read, cablen has been read from bytes 8-11

              [...]

              /* likely cabinet found -- try reading it */
              cab = sys->alloc(sys, sizeof(struct mscabd_cabinet_p); => an
    mscabd_cabinet_p entry will be allocated each time

              /* cabinet read correctly! */
              offset = caboff + cablen;
    => if cablen (and caboff) == 0, offset will be equal to 0

              [...]

              /* restart search */
              [...]
              length = 0;
              p = pend;
              state = 0;
    => if offset == 0, we will restart at the beginning of the file =>
    (because length == 0, so offset will still be zero in the next
      iteration)
              break;
          }
        }
      }

    If this function is called with a length value of zero, an infinite loop
    occurs. The comments above explain the scenario.

    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 denial of service or severe
    degradation of system performance. Ultimately, the OOM handler will
    terminate a task in order 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

    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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