Bug 144185

*** This bug has been split off bug 143505 ***

------- Original comment by Josh Bressers (Security Response Team) on 2004.12.21
14:08 -------

LibTIFF Directory Entry Count Integer Overflow Vulnerability*

iDEFENSE Security Advisory 12.21.04*
http://www.idefense.com/application/poi/display?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

The discoverer of this vulnerability wishes to remain anonymous.

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

X. LEGAL NOTICES

Copyright (c) 2004 iDEFENSE, Inc.

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Disclaimer: The information in the advisory is believed to be accurate
at the time of publishing based on currently available information. Use
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There are no warranties with regard to this information. Neither the
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