libtiff STRIPOFFSETS Integer Overflow Vulnerability

iDEFENSE Security Advisory 12.21.04
www.idefense.com/application/poi/display?id=173&type=vulnerabilities
December 21, 2004

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 (c) 2004 iDEFENSE, Inc.

Permission is granted for the redistribution of this alert
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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
of the information constitutes acceptance for use in an AS IS condition.
There are no warranties with regard to this information. Neither the
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or consequential loss or damage arising from use of, or reliance on,
this information.