Public Vulnerability Reports

Multiple Vendor xpdf JPX Stream Reader Heap Overflow Vulnerability

12.05.05

BACKGROUND

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

DESCRIPTION

Local exploitation of a heap-based buffer overflow vulnerability in
xpdf, as included by multiple vendor's software distributions, could
allow attackers to cause a denial of service (DoS) condition,
potentially resulting in arbitrary code execution.

The vulnerability specifically exists due to insufficient input
validation in the JPX Stream parsing code for decoding embedded JPEG
2000 images. The JPXStream::readCodestream function from
xpdf/JPXStream.cc takes the value of nXTiles and nYTiles from user-
controllable data from within the PDF file. The nXTiles and nYTiles
values are then used in a gmallocn() call as shown below.

GBool JPXStream::readCodestream(Guint len) {
...
    switch (segType) {
    case 0x4f:            // SOC - start of codestream
      // marker only
      break;
    case 0x51:            // SIZ - image and tile size
      if (!readUWord(&capabilities) ||
      !readULong(&img.xSize) ||
      !readULong(&img.ySize) ||
      !readULong(&img.xOffset) ||
      !readULong(&img.yOffset) ||
      !readULong(&img.xTileSize) ||
      !readULong(&img.yTileSize) ||
      !readULong(&img.xTileOffset) ||
      !readULong(&img.yTileOffset) ||
      !readUWord(&img.nComps)) {
        error(getPos(), "Error in JPX SIZ marker segment");
        return gFalse;
      }
...
      img.nXTiles = (img.xSize - img.xTileOffset + img.xTileSize - 1) /
        img.xTileSize;
      img.nYTiles = (img.ySize - img.yTileOffset + img.yTileSize - 1) /
        img.yTileSize;
 
      img.tiles = (JPXTile *)gmallocn(img.nXTiles * img.nYTiles,
        sizeof(JPXTile));

The values are used again later in JPEG format parsing code to copy
data from the file into a pre-allocated buffer in the heap. Overly
large values supplied to nXTiles and nYTiles result in corruption of
heap memory, which results in a DoS condition. This could result in
arbitrary code execution.

ANALYSIS

Exploitation could 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. Only then would the vulnerability be triggered.

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

WORKAROUND

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

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

CVE INFORMATION

The Common Vulnerabilities and Exposures (CVE) project has assigned the
name CAN-2005-3193 to this issue. This is a candidate for inclusion in
the CVE list (http://cve.mitre.org), which standardizes names for
security problems.

DISCLOSURE TIMELINE

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

CREDIT

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

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LEGAL NOTICES

Copyright © 2005 Verisign, Inc.

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