iDEFENSE Security Advisory 12.21.04: libtiff Directory Entry Count Integer Overflow Vulnerability

From: customer service mailbox (customerservice_at_idefense.com)
Date: 12/21/04

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    Date: Tue, 21 Dec 2004 17:09:26 -0500
    To: <bugtraq@securityfocus.com>, <vulnwatch@vulnwatch.org>
    
    

    libtiff Directory Entry Count Integer Overflow Vulnerability

    iDEFENSE Security Advisory 12.21.04
    www.idefense.com/application/poi/display?id=174&type=vulnerabilities
    December 21, 2004

    I. BACKGROUND

    This software provides support for the Tag Image File Format (TIFF), a
    widely used format for storing image data. Included in this software
    distribution is a library, libtiff, for reading and writing TIFF, a
    small collection of tools for doing simple manipulations of TIFF images
    on UNIX systems, and documentation on the library and tools. A small
    assortment of TIFF-related software for UNIX that has been contributed
    by others is also included.

    More information is available at the following site:
    http://www.remotesensing.org/libtiff/

    II. DESCRIPTION

    Remote exploitation of a heap-based buffer overflow vulnerability
    within the LibTIFF package could allow attackers to execute arbitrary
    code.

    The vulnerability specifically exists due to insufficient validation of
    user-supplied data when calculating the size of a directory entry. A
    TIFF file includes a number of directory entry header fields that
    describe the data in the file. Included in these entries is an entry
    count and offset value that are calculated to determine the size and
    location of the data for that entry. If the directory entry type is
    TIFF_ASCII or TIFF_UNDEFINED, the a call to CheckMalloc is made in
    order to allocate space for the entry contents as shown below from
    tif_dirread.c:

    cp = CheckMalloc(tif, dp->tdir_count+1, 1, mesg);
    if( (ok = (cp && TIFFFetchString(tif, dp, cp))) != 0 )
        cp[dp->tdir_count] = '\0'; /* XXX */

    If the tdir_count is set to 0xffffffff, the increment will cause the
    function call to allocate 0 bytes of memory and later memcpy calls will
    cause the buffer to overflow. An attacker may generate a malicious TIFF
    file which takes advantage of this unchecked calculation to execute
    arbitrary code with permissions of the user opening the TIFF file.

    III. ANALYSIS

    Remote attackers may be able to execute arbitrary code with permissions
    of the user opening the malformed TIFF file. The exposure to this
    vulnerability is mitigated by the fact that user interaction is
    required and that the user must view the malicious TIFF file in an
    application that is linked to a vulnerable version of libtiff.

    IV. DETECTION

    iDEFENSE has confirmed the existence of this vulnerability in LibTIFF
    3.5.7 and 3.7.0.

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

        - Debian Linux
        - Gentoo Linux
        - RedHat Linux
        - SuSE Linux
       
    V. WORKAROUND

    Only open TIFF files from trusted users or in an application not linked
    against vulnerable versions of libtiff.

    VI. VENDOR RESPONSE

    The following patch will address this vulnerability:

    --- tif_dirread.c.bak 2004-12-19 21:04:00.000000000 +0300
    +++ tif_dirread.c 2004-12-19 21:04:03.000000000 +0300
    @@ -71,7 +71,7 @@
             /*
              * XXX: Check for integer overflow.
              */
    - if (elem_size && bytes / elem_size == nmemb)
    + if (nmemb && elem_size && bytes / elem_size == nmemb)
                     cp = (char*)_TIFFmalloc(bytes);
     
             if (cp == NULL)

    (the same applies for tif_fax3.c)

    This patch has been incorporated into libtiff 3.7.1.

    VII. CVE INFORMATION

    A Mitre Corp. Common Vulnerabilities and Exposures (CVE) number has not
    been assigned yet.

    VIII. DISCLOSURE TIMELINE

    12/17/2004 Initial vendor notification
    12/17/2004 iDEFENSE clients notified
    12/21/2004 Coordinated public disclosure

    IX. CREDIT

    infamous41md[at]hotpop.com is credited with this discovery.

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

    X. LEGAL NOTICES

    Copyright (c) 2004 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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