Public Vulnerability Reports

Adobe Reader and Acrobat JBIG2 Encoded Stream Heap Overflow Vulnerability

03.24.09

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/

DESCRIPTION

Remote exploitation of a heap based buffer overflow vulnerability in Adobe Systems Inc.'s Reader and Acrobat could allow an attacker to execute arbitrary code with the privileges of the current user.

The vulnerability occurs when parsing a JBIG2-encoded stream inside of a PDF file. JBIG2 is an image encoding format that is primarily used for encoding monochrome images such as faxes.

When parsing the contents of a JBIG2 stream, a 32-bit value that represents the number of values in a table is used to allocate a heap buffer. This buffer is then filled with values from the file, without properly checking the bounds of the buffer. This leads to a heap based buffer overflow that can result in arbitrary code execution.

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.

Typically, heap based buffer overflows can be difficult to exploit due to modern heap implementations that perform heap integrity checks. However, Abode Reader and Acrobat use a custom heap allocator which can be abused to write arbitrary values to arbitrary locations. Labs testing has demonstrated this vulnerability is highly exploitable.

JavaScript is not required to exploit this vulnerability, however, it does make exploitation simpler.

DETECTION

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

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 in the vulnerable products. Follow best practice methodologies by avoiding opening files from untrusted or unsolicited sources. Deploy DEP (Data Execution Prevention). 

VENDOR RESPONSE

Adobe has released a patch which addresses this issue. For more information, consult their advisory (APSB09-04) at the following URL:

http://www.adobe.com/support/security/bulletins/apsb09-04.html

CVE INFORMATION

The Common Vulnerabilities and Exposures (CVE) project has assigned the name CVE-2009-0928 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

02/24/2009 - Initial Contact
02/24/2009 - Initial Response
02/24/2009 - PoC Requested
02/25/2009 - PoC Sent
03/06/2009 - Status update received - proposed release date of 03/18/2009
03/17/2009 - Vendor proposes new release date of 03/24/2009
03/24/2009 - Coordinated public disclosure

CREDIT

This vulnerability was discovered by Sean Larsson, iDefense Labs.

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LEGAL NOTICES

Copyright © 2009 Verisign, 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 customer service 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.