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Published:

23 December 2004

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             AUSCERT External Security Bulletin Redistribution

          ESB-2004.0816 -- iDEFENSE Security Advisories 12.21.04
              Two integer overflow vulnerabilities in libtiff
                             23 December 2004

===========================================================================

        AusCERT Security Bulletin Summary
        ---------------------------------

Product:           libtiff 3.7.0 and prior
Publisher:         iDEFENSE
Operating System:  UNIX variants
                   Linux variants
Impact:            Execute Arbitrary Code/Commands
Access:            Remote/Unauthenticated

Original Bulletin: http://www.idefense.com/application/poi/display?id=173
                   http://www.idefense.com/application/poi/display?id=174

Comment: This bulletin contains two separate iDEFENSE advisories describing 
         vulnerabilities in libtiff.

- --------------------------BEGIN INCLUDED TEXT--------------------

iDEFENSE Security Advisory 12.21.04:

I. BACKGROUND

libtiff provides support for the Tag Image File Format (TIFF), a widely
used format for storing image data.

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

II. DESCRIPTION

Remote exploitation of an integer overflow in libtiff may allow for the
execution of arbitrary code.

The overflow occurs in the parsing of TIFF files set with the
STRIPOFFSETS flag in libtiff/tif_dirread.c. In the TIFFFetchStripThing()
function, the number of strips (nstrips) is used directly in a
CheckMalloc() routine without sanity checking. The call ultimately boils
down to:

malloc(user_supplied_int*size(int32));

When supplied 0x40000000 as the user supplied integer, malloc is called
with a length argument of 0. This has the effect of returning the
smallest possible malloc chunk. A user controlled buffer is subsequently
copied to that small heap buffer, causing a heap overflow.

When exploited, it is possible to overwrite heap structures and seize
control of execution.

III. ANALYSIS

An attacker can exploit the above-described vulnerability to execute
arbitrary code under the permissions of the target user. Successful
exploitation requires that the attacker convince the end user to open
the malicious TIFF file using an application linked with a vulnerable
version of libtiff. Exploitation of this vulnerability against a remote
target is difficult because of the precision required in the attack.

IV. DETECTION

iDEFENSE has confirmed this vulnerability in libtiff 3.6.1. Changes were
introduced in libtiff 3.7.0 that had the effect of fixing this
vulnerability.

The following vendors provide susceptible libtiff packages within their
respective operating system distributions:
 
 - Gentoo Linux
 - Fedora Linux
 - RedHat Linux
 - SuSE Linux
 - Debian Linux

V. WORKAROUND

Only open TIFF files from trusted users.

VI. VENDOR RESPONSE

This issue is addressed in libtiff 3.7.0 and 3.7.1.

VII. CVE INFORMATION

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

VIII. DISCLOSURE TIMELINE

12/15/2004  Discovery of fix in later software version
12/21/2004  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 © 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.

- ---------------------------------------------------------------------------

libtiff Directory Entry Count Integer Overflow Vulnerability

iDEFENSE Security Advisory 12.21.04:

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 © 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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