[NT] Vulnerability in Cisco WebEx Meeting Manager ActiveX Control



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Vulnerability in Cisco WebEx Meeting Manager ActiveX Control
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SUMMARY

A buffer overflow vulnerability exists in an ActiveX control used by the
WebEx Meeting Manager. Exploitation of this vulnerability could allow a
remote attacker to execute arbitrary code on the user client machine. 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.

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 Universal Communication Format (UCF) contents. 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.

Note: In addition to the three currently maintained versions of WebEx
software, pre T23 software versions may also be impacted by this
vulnerability.

This vulnerability is documented in WebEx Bug IDs 292551 for WBS 26 and
306639 for WBS 25

CVE Information:
<http://www.cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2008-2737>
CVE-2008-2737

Identifying WebEx Meeting Service Version
The following procedure will allow a meeting participant to identify the
version of client software provided by a WebEx site. The procedure varies
slightly depending on the software version. The URL in all the following
examples is provided to meeting participants in the WebEx meeting
invitation.

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

For the WBS 26 version:
1. Browse to the WebEx meeting server at https://<sitename>.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://<sitename>.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://<sitename>.webex.com/version/wbxversionlist.do?siteurl=<sitename>

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 T23-based software. Affected WBS
23-based servers will be upgraded to fixed 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.

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

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.

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

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>
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 INFORMATION

The information has been provided by <mailto:psirt@xxxxxxxxx> Cisco
Systems Product Security Incident Response Team.
The original article can be found at:
<http://www.cisco.com/warp/public/707/cisco-sa-20080814-webex.shtml#@ID>
http://www.cisco.com/warp/public/707/cisco-sa-20080814-webex.shtml#@ID



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