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iDefense Security Advisory 01.12.09
http://labs.idefense.com/intelligence/vulnerabilities/ Jan 12, 2009
I. BACKGROUND The BlackBerry Enterprise Server is a suite of applications used to connect enterprise email and messaging services to BlackBerry device users. It consists of a variety of applications, one of which is the Attachment Service. This application is used to convert email attachments into a format that is easily rendered on BlackBerry devices. When a user requests an attachment on their BlackBerry device, the Attachment Service will obtain the attachment, parse and convert it, and then send it to the user for viewing. The Attachment Service is capable of converting a variety of different file formats, including PDF files. This vulnerability affects the PDF filter/distiller. For more information, see the vendor's site found at the following link.
II. DESCRIPTION Remote exploitation of a heap overflow vulnerability in Research In Motion Ltd. (RIM)'s BlackBerry Enterprise Server could allow an attacker to execute arbitrary code with the privileges of the affected service, usually SYSTEM.
The vulnerability occurs when parsing a certain stream inside of a PDF file. During parsing, a heap buffer is filled up with without properly checking to see whether the buffer is large enough to hold the current value. By inserting a large number of values, it is possible to overflow the buffer, and corrupt object pointers. This can lead to pointers being controlled, which results in the execution of arbitrary code.
III. ANALYSIS Exploitation of this vulnerability results in the execution of arbitrary code with the privileges of the Attachment Service, usually SYSTEM. In order to exploit this vulnerability, an attacker must email an enterprise BlackBerry user a malicious PDF file. Then, the user must attempt to view the file on their device. It is important to note that a user must request the attachment in order to trigger the parsing. It is not possible to exploit this vulnerability in a completely automated fashion without a user asking to view the file. However, after a user has requested the attachment, no further interaction is necessary.
Exploitation of heap overflow vulnerabilities on modern operating systems can be difficult due to heap integrity checks. However, the code in the PDF Distiller offers a wide variety of application specific targets for overwriting. By sculpting the heap it is possible place pointers in the buffer and use these to gain arbitrary code execution.
IV. DETECTION iDefense has confirmed the existence of this vulnerability in BlackBerry Enterprise Server version 4.1.5 and 4.1.6 (4.1 SP5, SP6). 4.1.6 is the most current version, as of the publishing of this report. This vulnerability was confirmed in BlackBerry Enterprise Server for Microsoft Exchange, but is believed to affect the Lotus and Novell versions as well. Previous versions may also be affected.
V. WORKAROUND It is possible to disable the PDF Distiller, which will prevent the conversion of PDF files by the Attachment Server. The following workaround was suggested by RIM for a previous PDF Distiller vulnerability, and has been verified to prevent the vulnerability described in this report. This workaround can be accomplished as follows:
To remove the PDF file extension from the list of supported file format extensions, complete the following actions:
After this, it is also necessary to completely disable the PDF distiller from loading, which will prevent an attacker from renaming a PDF to some other format extension. In order to do this, complete the following steps:
In Microsoft Exchange and Novell GroupWise environments, complete the following additional steps:
In IBM Lotus Domino environments, complete the following additional steps:
VI. VENDOR RESPONSE RIM has released a patch which addresses this issue. For more information, consult their advisories at the following URLs:
VII. CVE INFORMATION A Mitre Corp. Common Vulnerabilities and Exposures (CVE) number has not been assigned yet.
VIII. DISCLOSURE TIMELINE 12/17/2008 Initial Vendor Notification 12/17/2008 Initial Vendor Reply 12/17/2008 PoC Code Provided To Vendor 12/17/2008 Request Additional Information 01/06/2009 Additional Vendor Feedback 01/12/2009 Coordinated Public Disclosure
IX. CREDIT This vulnerability was discovered by Sean Larsson, iDefense Labs.
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X. LEGAL NOTICES 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 firstname.lastname@example.org 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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