Privacy and Legal Notice

CIAC INFORMATION BULLETIN

S-359: Vulnerability in Cisco WebEx Meeting Manager ActiveX Control

[Cisco Security Advisory Document ID: 107751]

August 18, 2008 18:00 GMT
[REVISED 10 Sep 2008]
PROBLEM: 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.
PLATFORM: WebEx Meeting Manager
DAMAGE: Execute arbitrary code
SOLUTION: Upgrade to the appropriate version.
VULNERABILITY
ASSESSMENT:		 The risk is MEDIUM. Exploitation of this vulnerability could allow a remote attacker to execute arbitrary code on the user client machine.
CVSS 2 BASE SCORE:
   TEMPORAL SCORE:
   VECTOR:		 7.5
6.2
(AV:N/AC:L/Au:N/C:P/I:P/A:P/E:F/RL:OF/RC:C)
LINKS:  
  CIAC BULLETIN: http://www.ciac.org/ciac/bulletins/s-359.shtml
  ORIGINAL BULLETIN: http://www.cisco.com/en/US/products/products_security_advisory09186a00809e2006.shtml
  CVE: CVE-2008-2737 
REVISION HISTORY:
09/10/2008 - revised S-359 to reflect changed Cisco made in Cisco Security Advisory
             Document ID: 107751 where they updated the Software Fixes section and 
			 updated to the software naming scheme.


[***** Start Cisco Security Advisory Document ID: 107751 *****]

Document ID: 107751


Advisory ID: cisco-sa-20080814-webex

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

Revision 1.3

Last Updated 2008 August 29 1530 UTC (GMT)

For Public Release 2008 August 14 2230 UTC (GMT)

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.

This advisory is posted at http://www.cisco.com/warp/public/707/cisco-sa-20080814-webex.shtml.

[Expand all sections]     [Collapse all sections]

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.

Top of the section     Close Section

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 WBS 23 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. This vulnerability has been assigned Common Vulnerabilities and Exposures (CVE) identifier CVE-2008-3558.

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 WBS 23-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:

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.

Top of the section     Close Section

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

Calculate the environmental score of 292551

CVSS Base Score - 9.3

Access Vector

Access Complexity

Authentication

Confidentiality Impact

Integrity Impact

Availability Impact

Network

Medium

None

Complete

Complete

Complete

CVSS Temporal Score - 8.4

Exploitability

Remediation Level

Report Confidence

Functional

Workaround

Confirmed

Top of the section     Close Section

Impact

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

Top of the section     Close Section

Software Versions and Fixes

The following table contains information on the WebEx meeting service software releases:

Software release

First Fixed release

WBS19

Vulnerable. Migrate to WBS25

WBS20

Vulnerable. Migrate to WBS25

WBS23

Vulnerable. Migration to WBS25 expected to be completed by the end of September 2008.

WBS25

Fixed release expected to be deployed by the end of September 2008.

WBS26

26.49.9.2838

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.

Top of the section     Close Section

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.

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}

Top of the section     Close Section

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

Top of the section     Close Section

Exploitation and Public Announcements

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

Exploit code has been made available.

Top of the section     Close Section

Status of this Notice: FINAL

THIS DOCUMENT IS PROVIDED ON AN "AS IS" BASIS AND DOES NOT IMPLY ANY KIND OF GUARANTEE OR WARRANTY, INCLUDING THE WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR USE. YOUR USE OF THE INFORMATION ON THE DOCUMENT OR MATERIALS LINKED FROM THE DOCUMENT IS AT YOUR OWN RISK. CISCO RESERVES THE RIGHT TO CHANGE OR UPDATE THIS DOCUMENT AT ANY TIME.

A stand-alone copy or Paraphrase of the text of this document that omits the distribution URL in the following section is an uncontrolled copy, and may lack important information or contain factual errors.

 Top of the section     Close Section

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.

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.

Top of the section     Close Section

Revision History

Revision 1.3

2008-August-29

Update to Software Fixes section and update to the software naming scheme.

Revision 1.2

2008-August-18

Updated CVE identifier.

Revision 1.1

2008-August-15

Addition of AMB link, adjustment of site terminology, and update of legacy software impact in Details section.

Revision 1.0

2008-August-14

Initial public release

 

 

 


[***** End Cisco Security Advisory Document ID: 107751 *****]
CIAC wishes to acknowledge the contributions of Cisco for the information contained in this bulletin.
DOE-CIRC can be contacted at: 
    Voice:          +1 866-941-2472 (7 x 24)
    E-mail:          doecirc@doecirc.energy.gov
    World Wide Web:  http://www.doecirc.energy.gov/