Software Engineering Institute

The Office Web Components Spreadsheet ActiveX control contains a code execution vulnerability. Public reports indicate that this vulnerability is being actively exploited.

Per the MSRC blog, the following products may install the affected control on a system:
Microsoft Office XP Service Pack 3, Microsoft Office 2003 Service Pack 3, Microsoft Office XP Web Components Service Pack 3, Microsoft Office Web Components 2003 Service Pack 3, Microsoft Office 2003 Web Components for the 2007 Microsoft Office system Service Pack 1, Microsoft Internet Security and Acceleration Server 2004 Standard Edition Service Pack 3, Microsoft Internet Security and Acceleration Server 2004 Enterprise Edition Service Pack 3, Microsoft Internet Security and Acceleration Server 2006, Internet Security and Acceleration Server 2006 Supportability Update, Microsoft Internet Security and Acceleration Server 2006 Service Pack 1, Microsoft Office Small Business Accounting 2006.
Further details are available from the Microsoft Security Research & Defense blog.

A remote attacker may be able to take control of a vulnerable system.

Install the updates described in Microsoft Security Bulletin MS09-043.

Disable the Office Web Components Spreadsheet ActiveX controls in Internet Explorer

The vulnerable controls can be disabled in Internet Explorer by setting the kill bit for the following CLSIDs:
{0002E541-0000-0000-C000-000000000046} (OWC10)
{0002E559-0000-0000-C000-000000000046} (OWC11)
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 these controls:

Windows Registry Editor Version 5.00

[HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Internet Explorer\ActiveX Compatibility\{0002E541-0000-0000-C000-000000000046}]
"Compatibility Flags"=dword:00000400
[HKEY_LOCAL_MACHINE\SOFTWARE\Wow6432Node\Microsoft\Internet Explorer\ActiveX Compatibility\{0002E541-0000-0000-C000-000000000046}]
"Compatibility Flags"=dword:00000400

[HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Internet Explorer\ActiveX Compatibility\{0002E559-0000-0000-C000-000000000046}]
"Compatibility Flags"=dword:00000400
[HKEY_LOCAL_MACHINE\SOFTWARE\Wow6432Node\Microsoft\Internet Explorer\ActiveX Compatibility\{0002E559-0000-0000-C000-000000000046}]
"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.