iDefense Security Advisory 01.13.09: RIM BlackBerry Enterprise Server Attachment Service PDF Distiller 'bitmaps' Heap Overflow Vulnerability
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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 data stream inside of a PDF
file. During parsing, a dynamic array is filled up with pointers to
certain objects without properly checking to see whether the array is
large enough to hold all of the pointers. By inserting a large number
of pointers, it is possible to overflow the array, and corrupt object
pointers. This can lead to the EIP register 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 e-mail 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.
In Labs testing, it was possible to gain code execution, albeit
unreliably. It is likely that with additional heap sculpting reliable
code execution is possible.
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
Research In Motion (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.
Get paid for vulnerability research
http://labs.idefense.com/methodology/vulnerability/vcp.php
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http://labs.idefense.com/
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 customerservice@xxxxxxxxxxxx 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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