I. BACKGROUND

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.

http://www.adobe.com/products/reader/ http://www.adobe.com/products/acrobatpro/

II. DESCRIPTION

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.

III. ANALYSIS

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.

IV. DETECTION

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

V. WORKAROUND

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)

VI. VENDOR RESPONSE

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

http://www.adobe.com/support/security/bulletins/apsb09-07.html

VII. CVE INFORMATION

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 (http://cve.mitre.org/), which standardizes names for security problems.

VIII. DISCLOSURE TIMELINE

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

IX. CREDIT

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

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X. LEGAL NOTICES

Copyright © 2009 iDefense, Inc.

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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.