From the Cisco Security Advisory :
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.
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.
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:
- Browse to the WebEx meeting server at https://<sitename>.webex.com/.
- Select Support from the left side of the web page.
- Select Downloads from the left side of the web page.
- 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:
- Browse to the WebEx meeting server at https://<sitename>.webex.com/.
- Select Assistant on the left side of the page.
- Select the Support link.
- Select the Version link, which is displayed on the right side of the top of the page.
- 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:
- 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.
No other Cisco products are currently known to be affected by this vulnerability.
