Multiple Vendor xpdf DCTStream Baseline Heap Overflow Vulnerability

iDefense Security Advisory 12.05.05
www.idefense.com/application/poi/display?id=342&type=vulnerabilities
December 5, 2005

I. BACKGROUND

Xpdf is an open-source viewer for Portable Document Format (PDF) files.

II. DESCRIPTION

Local exploitation of a heap-based buffer overflow vulnerability in 
xpdf, as included in various vendors' operating system distributions, 
could allow attackers to cause a denial of service condition, 
potentially resulting in arbitrary code execution. 

The vulnerability specifically exists due to insufficient input 
validation in the DCT stream parsing code. The 
DCTStream::readBaselineSOF function from xpdf/Stream.cc takes the value 
of numComps from user-controllable data from within the PDF file. The 
numComps value is used in a loop to copy data from the file into a pre-
allocated buffer in the heap, shown as follows:

GBool DCTStream::readBaselineSOF() {
...
  numComps = str->getChar();
...
  for (i = 0; i < numComps; ++i) {
    compInfo[i].id = str->getChar();
    c = str->getChar();
    compInfo[i].hSample = (c >> 4) & 0x0f;
    compInfo[i].vSample = c & 0x0f;
    compInfo[i].quantTable = str->getChar();
  }
...

Overly large values supplied to numComps will result in corruption of 
heap memory resulting in a DoS condition, potentially resulting in 
arbitrary code execution.

III. ANALYSIS

Successful exploitation of this vulnerability can result in arbitrary 
code execution with privileges of the xpdf process. Currently, 
exploitation resulting in code execution is theoretical and dependant 
on the process memory layout. A typical exploitation attempt would 
require an attacker to supply a malicious .pdf to the victim. The 
victim would need to open the corrupt .pdf file in xpdf, triggering the 
vulnerability. 

IV. DETECTION

iDefense has confirmed the existence of this vulnerability in xpdf 
3.01. All earlier versions of xpdf are suspected vulnerable.

The following vendors include susceptible xpdf packages within their 
operating system distributions:

    . The Debian Project: Linux 3.0 and 3.1 

V. WORKAROUND

iDefense is currently unaware of any effective workarounds for this 
vulnerability.

VI. VENDOR RESPONSE

A patch for this vulnerability is available at:
  
  ftp://ftp.foolabs.com/pub/xpdf/xpdf-3.01pl1.patch

Updated binaries (version 3.01pl1) are available at:

  http://www.foolabs.com/xpdf/download.html

VII. CVE INFORMATION

The Common Vulnerabilities and Exposures (CVE) project has assigned the
name CAN-2005-3191 to this issue. This is a candidate for inclusion in
the CVE list (http://cve.mitre.org), which standardizes names for
security problems.

VIII. DISCLOSURE TIMELINE

10/13/2005  Initial vendor notification
10/19/2005  Initial vendor response
12/05/2005  Coordinated public disclosure

IX. CREDIT

iDefense credits infamous41md@hotpop.com with the discovery of this 
vulnerability.

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X. LEGAL NOTICES

Copyright C 2005 iDefense, Inc.

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at the time of publishing based on currently available information. Use
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