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 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@xxxxxxxxxxxx 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.
