Public Vulnerability Reports

Adobe Reader and Acrobat FlateDecode Integer Overflow Vulnerability



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 difficult.

 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 Labs

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Copyright © 2009 Verisign, Inc.

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