[Full-disclosure] iDEFENSE Security Advisory 06.29.05: Clam AntiVirus ClamAV Cabinet 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 10:49:10 -0400
To: <bugtraq@securityfocus.com>, <vulnwatch@vulnwatch.org>, <full-disclosure@lists.grok.org.uk>

    Clam AntiVirus ClamAV Cabinet File Handling DoS Vulnerability

    iDEFENSE Security Advisory 06.29.05
    www.idefense.com/application/poi/display?id=275&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
    cabinet file format is a Microsoft archive format used for distributing
    Microsoft software.

    The vulnerability specifically exists due to insufficient validation on
    cabinet file header data. The ENSURE_BITS() macro fails to check for
    zero length reads, allowing a carefully constructed cabinet file to
    cause an infinite loop. The ENSURE_BITS() macro is executed indirectly
    through the READ_BITS macro and is called from the mszipd_compress
    function. The vulnerable code from libclamav/mspack/mszipd.c is
    detailed below:

    #define ENSURE_BITS(nbits) do { \
      while (bits_left < (nbits)) { \
        if (i_ptr >= i_end) { \
          if (zipd_read_input(zip)) return zip->error; \
          i_ptr = zip->i_ptr; \
          i_end = zip->i_end; \
        } \
        bit_buffer |= *i_ptr++ << bits_left; bits_left += 8; \
      } \
    } while (0)

    #define READ_BITS(val, nbits) do { \
      ENSURE_BITS(nbits); (val) = PEEK_BITS(nbits); REMOVE_BITS(nbits); \
    } while (0)

    static int zipd_read_input(struct mszipd_stream *zip) {
      int read = zip->sys->read(zip->input,
                                      &zip->inbuf[0], (int)zip->inbuf_size);
      if (read < 0) return zip->error = MSPACK_ERR_READ;
      zip->i_ptr = &zip->inbuf[0];
      zip->i_end = &zip->inbuf[read];

      return MSPACK_ERR_OK;
    }

    int mszipd_decompress(...)
    {
      [...]
      do {
        READ_BITS(i, 8);
        if (i == 'C') state = 1;
        else if ((state == 1) && (i == 'K')) state = 2;
        else state = 0;
      } while (state != 2);
      [...]
    }

    Modification of the cffile_FolderOffset to 0xff in a CAB file can cause
    a read of zero, resulting in the infinite loop.

    III. ANALYSIS

    ClamAV is used in a number of mail gateway products. 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 infinate loop will cause the ClamAV
    software to use all available processor resources, resulting in a
    denial of service or severe degradation to system performance. 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-2005-1923 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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