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Vulnerability Note VU#661827

Cisco WebEx Meeting Manager WebexUCFObject ActiveX Control stack buffer overflow

Overview

The WebexUCFObject ActiveX control, which comes with Cisco WebEx Meeting Manager, contains a stack buffer overflow, which can allow a remote, unauthenticated attacker to execute arbitrary code on a vulnerable system.

I. Description

Cisco WebEx is an online meeting and collaboration software package. WebEx Meeting Manager is the client-side application that is used by the WebEx meeting service. WebEx Meeting Manager includes an ActiveX control called WebexUCFObject, which is provided by the file atucfobj.dll. The WebexUCFObject ActiveX control contains a stack buffer overflow in the NewObject() method.

Limited testing has indicated that not every version of the WebexUCFObject ActiveX control is marked as Safe For Scripting, which means that some versions of the control may not be exploitable by using a default configuration of Internet Explorer. The Cisco Security Advisory indicates that WBS 23, WBS25, and WBS26 are vulnerable.

II. Impact

By convincing a user to view a specially crafted HTML document (e.g., a web page or an HTML email message or attachment), an attacker may be able to execute arbitrary code with the privileges of the user.

III. Solution

Apply an update

The Cisco Security Advisory indicates that WebEx meeting participants will automatically receive a fixed version of atucfobj.dll when they join a meeting on a server with fixed software. Version 26.49.9.2838 is the first fixed version for WBS 26 users.

Disable the WebexUCFObject ActiveX control in Internet Explorer

The vulnerable ActiveX control can be disabled in Internet Explorer by setting the kill bit for the following CLSID:

    {E06E2E99-0AA1-11D4-ABA6-0060082AA75C}
More information about how to set the kill bit is available in Microsoft Support Document 240797. Alternatively, the following text can be saved as a .REG file and imported to set the kill bit for this control:
    Windows Registry Editor Version 5.00

    [HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Internet Explorer\ActiveX Compatibility\{E06E2E99-0AA1-11D4-ABA6-0060082AA75C}]
    "Compatibility Flags"=dword:00000400
Disable ActiveX

Disabling ActiveX controls in the Internet Zone (or any zone used by an attacker) appears to prevent exploitation of this and other ActiveX vulnerabilities. Instructions for disabling ActiveX in the Internet Zone can be found in the "Securing Your Web Browser" document. 

Systems Affected
VendorStatusDate Updated
Cisco Systems, Inc.Vulnerable15-Aug-2008
WebEx Communications, INCVulnerable15-Aug-2008

References


http://www.cisco.com/warp/public/707/cisco-sa-20080814-webex.shtml
http://secunia.com/advisories/31397/
http://lists.grok.org.uk/pipermail/full-disclosure/2008-August/063692.html

Credit

This vulnerability was publicly reported by Elazar Broad.

This document was written by Will Dormann.

Other Information

Date Public08/07/2008
Date First Published08/15/2008 01:44:50 PM
Date Last Updated08/15/2008
CERT Advisory 
CVE NameCVE-2008-3558, CVE-2008-2737
Metric30.07
Document Revision6

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Copyright 2008 Carnegie Mellon University