Multiple Vendor xpdf PDF Viewer Buffer Overflow Vulnerability 
 
iDEFENSE Security Advisory 12.21.04
www.idefense.com/application/poi/display?id=172&type=vulnerabilities
December 21, 2004
 
I. BACKGROUND
 
Xpdf is an open-source viewer for Portable Document Format (PDF) files.
 
II. DESCRIPTION
 
Remote exploitation of a buffer overflow vulnerability in the xpdf PDF 
viewer, as included in multiple Linux distributions, could allow 
attackers to execute arbitrary code as the user viewing a PDF file. The 
offending code can be found in the Gfx::doImage() function in the source
 
file xpdf/Gfx.cc. 
 
void Gfx::doImage(Object *ref, Stream *str, GBool inlineImg) {
  Dict *dict;
  int width, height;
  int bits;
  GBool mask;
  GBool invert;
  GfxColorSpace *colorSpace;
  GfxImageColorMap *colorMap;
  Object maskObj;
  GBool haveMask;
  int maskColors[2*gfxColorMaxComps];
  Object obj1, obj2;
  int i;
 
  ...
    // get the mask
    haveMask = gFalse;
    dict->lookup("Mask", &maskObj);
        if (maskObj.isArray()) {
          for (i = 0; i < maskObj.arrayGetLength(); ++i) {
        maskObj.arrayGet(i, &obj1);
[!]         maskColors[i] = obj1.getInt();
            obj1.free();
          }
          haveMask = gTrue;
        }
  ...
}  
 
 
Due to the fact that the loop boundaries are not less than the storage 
area, the maskColors array is eventually filled up. After that, local 
variables and other stack memory is overwritten. This ultimately leads 
to control of program flow and arbitrary code execution.
 
III. ANALYSIS
 
The severity of this issue is mitigated by the fact that several of the 
local overwritten variables in doImage() are referenced prior to EIP 
being restored; therefore, before the attack gains control of the target
 
process. However, an attacker with knowledge of the remote operating 
system can construct and validate a malicious payload before attempting 
exploitation, thus increasing the chances of success. An attacker must 
convince a target user to open the malicious file to exploit this 
vulnerability.
 
IV. DETECTION
 
iDEFENSE has confirmed the existence of this vulnerability in version 
3.00 of xpdf. It is suspected previous versions are also vulnerable. 
 
The following Linux distributions are affected by this vulnerability:
 
	SUSE Linux 
	Redhat Linux 
	Fedora Linux 
	Debian Linux 
	Gentoo Linux 
	FreeBSD (ports) 
	OpenBSD 
 
V. WORKAROUND
 
Only open PDF files from trusted individuals.
 
VI. VENDOR RESPONSE
 
A patch to address this vulnerability is available from:
 
    ftp://ftp.foolabs.com/pub/xpdf/xpdf-3.00pl2.patch
 
Updated binaries (version 3.00pl2) are available from:
 
    http://www.foolabs.com/xpdf/download.html
 
VII. CVE INFORMATION
 
The Common Vulnerabilities and Exposures (CVE) project has assigned the
names CAN-2004-1125 to these issues. This is a candidate for inclusion
in the CVE list (http://cve.mitre.org), which standardizes names for
security problems.
 
VIII. DISCLOSURE TIMELINE
 
11/23/2004  Initial vendor notification
11/29/2004  Initial vendor response
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.
 
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.