iDefense Security Advisory 01.13.09: RIM BlackBerry Enterprise Server Attachment Service PDF Distiller 'symWidths' Heap Overflow Vulnerability

[iDefense Labs <labs-no-reply@xxxxxxxxxxxx>]

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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.

http://na.blackberry.com/eng/services/server/

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:

   1. From the Windows Desktop, open the BlackBerry Server Configuration
tool.
   2. Click the Attachment Server tab.
   3. In the Format Extensions field, delete pdf: from the colon
delimited list of extensions.
   4. Click Apply.
   5. Click OK.

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:

   1. On the Windows Desktop, open the BlackBerry Server Configuration tool.
   2. Click the Attachment Server tab.
   3. In the Configuration Option drop-down list, select Attachment Server.
   4. In the Distiller Settings section, next to the distiller name
Adobe PDF, clear the check box in the Enabled column.
   5. Click Apply.
   6. Click OK.
   7. On the Windows Desktop, in Administrative Tools, open Services.
   8. Right-click BlackBerry Attachment Service and click Stop.
   9. Right-click BlackBerry Attachment Service and click Start.
  10. Close Services.

In Microsoft Exchange and Novell GroupWise environments, complete the
following additional steps:

   1. On the Windows Desktop, in Administrative Tools, open Services.
   2. Right-click BlackBerry Dispatcher and click Stop.
   3. Right-click BlackBerry Dispatcher and click Start.
   4. Close Services.

In IBM Lotus Domino environments, complete the following additional
steps:

   1. Open the IBM Lotus Domino Administrator.
   2. Click the Server tab.
   3. Click the Status tab.
   4. Click Server Console.
   5. In the Domino Command field, type tell BES quit and press ENTER.
   6. In the Domino Command field, type load BES and press ENTER.
   7. Close the IBM Lotus Domino Administrator.

VI. VENDOR RESPONSE

RIM has released a patch which addresses this issue. For more
information, consult their advisories at the following URLs:

http://www.blackberry.com/btsc/search.do?cmd=displayKC&docType=kc&externalId=KB17118

http://www.blackberry.com/btsc/search.do?cmd=displayKC&docType=kc&externalId=KB17119

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
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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.
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