[c-nsp] Cisco Security Advisory: Vulnerability in Cisco WebEx Meeting Manager ActiveX Control

Thu Aug 14 23:15:00 EDT 2008

An ActiveX control (atucfobj.dll) that is used by the Cisco WebEx
Meeting Manager contains a buffer overflow vulnerability that may
result in a denial of service or remote code execution. The WebEx
Meeting Manager is a client-side program that is provided by the
Cisco WebEx meeting service. The Cisco WebEx meeting service
automatically downloads, installs, and configures Meeting Manager the
first time a user begins or joins a meeting.

When users connect to the WebEx meeting service, the WebEx Meeting
Manager is automatically upgraded to the latest version. There is a
manual workaround available for users who are not able to connect to
the WebEx meeting service.

Cisco WebEx is in the process of upgrading the meeting service
infrastructure with fixed versions of the affected file.

This advisory is posted at:

http://www.cisco.com/warp/public/707/cisco-sa-20080814-webex.shtml

Affected Products
=================

Vulnerable Products
+------------------

The WebEx Meeting Manager downloads several components to meeting
participants before they join a WebEx meeting. The vulnerability in
this Security Advisory affects the atucfobj.dll library.

Products Confirmed Not Vulnerable
+--------------------------------

No other Cisco products are currently known to be affected by this
vulnerability.

Details
=======

The WebEx meeting service is a hosted multimedia conferencing
solution that is managed by and maintained by Cisco WebEx. When a
meeting participant connects to the WebEx meeting service through a
web browser, the WebEx meeting service installs several components of
the WebEx Meeting Manager browser plugin on the meeting participant's
system.

WebEx Meeting Manager includes atucfobj.dll, a DLL that allows
meeting participants to view Unicode fonts. This library contains a
buffer overflow vulnerability that could allow an attacker to execute
arbitrary code.

The WebEx meeting service currently maintains three different
versions of software. WebEx meeting service servers run one of the
following versions: WBS 23, WBS 25, or WBS 26.

This vulnerability is documented in WebEx Bug IDs 292551 for WBS 26
and 306639 for WBS 25. This vulnerability has been assigned Common
Vulnerabilities and Exposures (CVE) identifier CVE-2008-2737.

Identifying WebEx Meeting Service Version
+----------------------------------------

The following procedure allows meeting participants to identify the
version of client software that is provided by a WebEx server. The
procedure varies slightly depending on the version of the WebEx
server software. The URL in all the following examples is provided to
meeting participants as part of the WebEx meeting invite.

Client build numbers adhere to the format of XX.YY.ZZ.WWWW. The first
number indicates the major version number of the software build. For
example, a client build number of 26.49.9.2838 indicates a WBS
26-based software version.

For the WBS 26 version:

 1. Browse to the WebEx meeting server at
    https://<servername>.webex.com/.
 2. Select Support from the left side of the web page.
 3. Select Downloads from the left side of the web page.
 4. The version of the client software that is provided by the server
    is listed next to Client build.

For WebEx servers that are running WBS 26, the first fixed version is
26.49.9.2838. Client build versions prior to 26.49.9.2838 are
vulnerable.

For the WBS 25 version:

 1. Browse to the WebEx meeting server at
    https://<servername>.webex.com/.
 2. Select Assistant on the left side of the page.
 3. Select the Support link.
 4. Select the Version link, which is displayed on the right side of
    the top of the page.
 5. The Client Build version is displayed in a pop-up window.

There is currently no fixed version for the WBS 25-based WebEx
meeting service. This section of the Security Advisory will be
updated when fixed version information is available.

For the WBS 23 version:

Servers that run WBS 23-based WebEx meeting service display version
information using the following URL format:

https://<servername>.webex.com/version/wbxversionlist.do?siteurl=<servername>

On the redisplayed page the Client versions in files field will
indicate the Client Build.

For example: The 'T23' in WBXclient-T23L10NSP33EP13-1092.txt
indicates a WBS 23-based system.

Cisco WebEx is not planning to repair WBS 23-based software. Affected
WBS 23-based servers will be upgraded to fixed WBS 25 or WBS 26-based
software.

Attack Vector Details
+--------------------

This Security Advisory addresses a vulnerable ActiveX control
(atucfobj.dll). If atucfobj.dll is present on a client's computer, it
may be possible for an attacker to embed malicious code into HTML
content that calls an affected function in atucfobj.dll via ActiveX.

Users could encounter the malicious HTML in several ways. The most
common manners are:

  * Browsing to a web-site that contains the malicious content

  * HTML that is embedded in e-mail messages

  * HTML that is delivered via instant messaging applications

WebEx Upgrade Timeline
+---------------------

Upgrades from WBS 23 versions to WBS 26 are expected to be complete
by the end of September 2008.

Fixed versions of WBS 25 are expected to be deployed by the end of
September 2008.

Deployed versions of WBS 26 are fixed.

Vulnerability Scoring Details
=============================

Cisco has provided scores for the vulnerabilities in this advisory
based on the Common Vulnerability Scoring System (CVSS). The CVSS
scoring in this Security Advisory is done in accordance with CVSS
version 2.0.

CVSS is a standards-based scoring method that conveys vulnerability
severity and helps determine urgency and priority of response.

Cisco has provided a base and temporal score. Customers can then
compute environmental scores to assist in determining the impact of
the vulnerability in individual networks.

Cisco has provided an FAQ to answer additional questions regarding
CVSS at:

http://www.cisco.com/web/about/security/intelligence/cvss-qandas.html

Cisco has also provided a CVSS calculator to help compute the
environmental impact for individual networks at:

http://intellishield.cisco.com/security/alertmanager/cvss

The CVSS scoring for WebEx bug IDs 292551 and 306639 are identical
because they reference the same vulnerability. The below scoring
applies to both 292551 and 306639.

ActiveX Vulnerability in WebEx Meeting Manager

CVSS Base Score - 9.3
    Access Vector - Network
    Access Complexity - Medium
    Authentication - None
    Confidentiality Impact - Complete
    Integrity Impact - Complete
    Availability Impact - Complete

CVSS Temporal Score - 8.4
    Exploitability - Functional
    Remediation Level - Official Fix
    Report Confidence - Confirmed

Impact
======

Successful exploitation of the vulnerability may result in execution
of arbitrary code.

Software Versions and Fixes
===========================

The WebEx meeting service currently maintains three different
versions of software. WebEx meeting service servers run one of the
following versions: WBS 23, WBS 25, or WBS 26. Clients will receive
an upgrade automatically in accordance with the process that is
outlined in the Obtaining Fixed Software section of this advisory
within the time frame that is outlined in the WebEx Upgrade Timeline
subsection of this advisory.

Cisco WebEx will not offer the modified atucfobj.dll as a separate
download.

Workarounds
===========

WebEx meeting participants who join a WebEx meeting that is hosted by
a server with fixed software will download a fixed version of
atucfobj.dll prior to joining the meeting.

Several other workarounds are described below in the following
subsections.

Manually Upgrading WebEx Meeting Manager
+---------------------------------------

Users can verify that the WebEx meeting service server they are
connecting to is running fixed code via the method that is described
in the subsection entitled Identifying WebEx Version subsection of
the Details section of this Security Advisory.

If the WebEx server is running a version of software that is fixed,
users can manually download and install the Meeting Manager client to
ensure their versions of atucfobj.dll are not vulnerable.

Removing WebEx Meeting Manager
+-----------------------------

It is possible to remove the WebEx Meeting Manager component from
Microsoft Windows by using the Add or Remove Programs utility in the
Windows Control Panel:

 1. In Windows, choose Start > Control Panel.
 2. Double-click Add or Remove Programs.
 3. Double-click WebEx.
 4. In the pop-up menu, check the Meeting Manager box and click 
    Uninstall.
 5. Follow the prompts to complete the uninstall process and restart
    the system.

NOTE: After uninstalling the WebEx Meeting Manager, users that join a
WebEx meeting that is hosted by a vulnerable version will again
download and install a vulnerable atucfobj.dll.

Disabling atucfobj.dll by Setting the Kill Bit
+---------------------------------------------

It is possible to disable the execution of atucfobj.dll by using a
configuration setting in Microsoft Windows. This method is called
setting the kill bit for the DLL. Once set, this method prevents
atucfobj.dll from loading, which prevents exploitation of the
vulnerability.

Instructions for setting the kill bit in Microsoft Windows are
available at the following location:

http://support.microsoft.com/kb/240797

Setting the kill bit for atucfobj.dll will persist even after a fixed
version of the DLL is installed. To re-enable the use of
atucfobj.dll, the kill bit will need to be unset.

To disable atucfobj.dll users must know the CLSID for the DLL. The
CLSID for atucfobj.dll is {32E26FD9-F435-4A20-A561-35D4B987CFDC}

Additional mitigation techniques that can be deployed on Cisco
devices within the network are available in the Cisco Applied
Mitigation Bulletin companion document for this advisory:

http://www.cisco.com/warp/public/707/cisco-amb-20080814-webex.shtml

Obtaining Fixed Software
========================

As outlined in WebEx Upgrade Timeline section, WebEx meeting
participants who join a WebEx meeting that is hosted by a server with
fixed software will automatically download a fixed version of
atucfobj.dll prior to joining the meeting.

Clients can also upgrade manually by following the instructions in
the Manually Upgrading WebEx Meeting Manager subsection of the
Workarounds section of this advisory.

Clients can protect themselves without first accessing a WebEx server
by following the instructions in the Removing WebEx Meeting Manager
subsection of the Workarounds section of this advisory.

Customers that need additional information can contact WebEx Global
Support Services and Technical Support. WebEx Global Support Services
and Technical Support can be reached through the WebEx support site
at http://support.webex.com/support/support-overview.html or by phone
at +1-866-229-3239 or +1-408-435-7088.

Customers outside of the United States can reference the following
link for local support numbers:

http://support.webex.com/support/phone-numbers.html

Exploitation and Public Announcements
=====================================

This issue has been publicly announced on multiple external forums
and mailing lists.

Exploit code has been made available.

Status of this Notice: FINAL

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factual errors.

Distribution
============

This advisory is posted on Cisco's worldwide website at:

http://www.cisco.com/warp/public/707/cisco-sa-20080814-webex.shtml

In addition to worldwide web posting, a text version of this notice
is clear-signed with the Cisco PSIRT PGP key and is posted to the
following e-mail and Usenet news recipients.

  * cust-security-announce at cisco.com
  * first-bulletins at lists.first.org
  * bugtraq at securityfocus.com
  * vulnwatch at vulnwatch.org
  * cisco at spot.colorado.edu
  * cisco-nsp at puck.nether.net
  * full-disclosure at lists.grok.org.uk
  * comp.dcom.sys.cisco at newsgate.cisco.com

Future updates of this advisory, if any, will be placed on Cisco's
worldwide website, but may or may not be actively announced on
mailing lists or newsgroups. Users concerned about this problem are
encouraged to check the above URL for any updates.

Revision History
================

+---------------------------------------+
| Revision |                | Initial   |
| 1.0      | 2008-August-14 | public    |
|          |                | release   |
+---------------------------------------+

Cisco Security Procedures
=========================

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