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Date: Thu, 11 Jun 2009 15:32:45 -0500
From: iDefense Labs <>
Subject: iDefense Security Advisory 06.11.09: Adobe Reader and Acrobat FlateDecode
 Integer Overflow Vulnerability

iDefense Security Advisory 06.09.09
Jun 09, 2009


Adobe Acrobat Reader/Acrobat are programs for viewing and editing
Portable Document Format (PDF) documents. For more information, see the
vendor's site found at the following link.


Remote exploitation of an integer overflow vulnerability in multiple
versions of Adobe Systems Inc's Reader and Acrobat PDF reader and
processor could allow an attacker to execute arbitrary code with the
privileges of the current user.

The vulnerability occurs when parsing a FlateDecode filter inside a PDF
file. FlateDecode is a filter for data compressed with zlib deflate
compression method. Several parameters can be specified for the
FlateDecode filter. Those values are used in an arithmetic operation
that calculates the number of bytes to allocate for a heap buffer. This
calculation can overflow, which results in an undersized heap buffer
being allocated. This buffer is then overflowed with data decompressed
from the FlateDecode stream. This leads to a heap-based buffer overflow
that can result in arbitrary code execution.


Exploitation of this vulnerability allows the attacker to execute
arbitrary code with the privileges of the user opening the file. The
attacker will have to create a malicious PDF file and convince the
victim to open it. This can be accomplished by embedding the PDF file
into an IFRAME inside of a Web page, which will result in automatic
exploitation once the page is viewed. The file could also be e-mailed
as an attachment or placed on a file share. In these cases, a user
would have to manually open the file to trigger exploitation. If
preview is enable in Windows Explorer, this vulnerability can be
triggered simply by accessing a folder containing PDF files.


Acrobat Reader and Acrobat Professional versions 7.1.0, 8.1.3, 9.0.0 and
prior versions are vulnerable.


None of the following workarounds will prevent exploitation, but they
can reduce potential attack vectors and make exploitation more

  Prevent PDF documents from being opened automatically by the Web browser
  Disable JavaScript
  Disable PDFShell extention by removing or renaming Acrord32info.exe file.
  Follow best practice methodologies by avoiding opening files from
untrusted or unsolicited sources
  Deploy DEP (Data Execution Prevention)


Adobe has released a patch which addresses this issue. For more
information, consult their advisory (APSB09-07) at the following URL:


The Common Vulnerabilities and Exposures (CVE) project has assigned the
name CVE-2009-1856 to this issue. This is a candidate for inclusion in
the CVE list (, which standardizes names for
security problems.


02/25/2009  - Initial Contact
02/25/2009  - Initial Response
02/25/2009  - PoC Requested
02/25/2009  - PoC Sent
06/05/2009  - Tentative disclosure date of 06/09/2009 set
06/09/2009  - Coordinated public disclosure


This vulnerability was discovered by Jun Mao and Ryan Smith, iDefense

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Copyright © 2009 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 e-mail 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.

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