Vulnerabilities in Word and Excel Document Parsing

Severity: High

10 August, 2010

Summary:

• These vulnerabilities affect: All current versions of Microsoft Office for Windows and Mac (specifically Word and Excel)
• How an attacker exploits them: By enticing you to open maliciously crafted Office documents
• Impact: An attacker can execute code, potentially gaining complete control of your computer
• What to do: Install the appropriate Office patches immediately

Exposure:

(Editor’s note: Due to an unforeseen technical difficulty, we were unable to post and email the LiveSecurity alerts that were written for Microsoft Patch Day. Please see yesterday’s Wire post)

Today, Microsoft released two security bulletins describing five vulnerabilities found in components or programs that ship with Microsoft Office for Windows and Mac. Some of the vulnerabilities also affect Word Viewer, the Office Compatibility Packs, and the Open XML File Format Converter for Mac. Each vulnerability affects different versions of Office to a different extent. The five flaws affect different components and applications within Office, but the end result is always the same – by enticing one of your users into downloading and opening a maliciously crafted Office document, an attacker can exploit any of these vulnerabilities to execute code on a victim’s computer, usually inheriting that user’s level of privileges and permissions. If your user has local administrative privileges, the attacker gains full control of the user’s machine.

According to Microsoft’s bulletins, an attacker can exploit these flaws using two types of Office documents: Word (.doc) and Excel (.xls). So beware of all unexpected documents you receive with these file extensions.

If you’d like to learn more about each individual flaw, drill into the “Vulnerability Details” section of the security bulletins listed below:

• MS10-056: Multiple Word Code Execution Vulnerabilities, rated Critical
• MS10-057: Excel Code Execution Vulnerability, rated Important

Solution Path

Microsoft has released patches for Office to correct all of these vulnerabilities. You should download, test, and deploy the appropriate patches throughout your network immediately.

Word update for:

• Office XP w/SP3
• Office 2003 w/SP3
• 2007 Microsoft Office System w/SP1
• Office 2004 for Mac
• Office 2008 for Mac
• Open XML File Format Converter for Mac
• Microsoft Office Word Viewer
• Microsoft Office Compatibility Pack for Word, Excel, and PowerPoint 2007 File Formats Service Pack 2
• Microsoft Works 9

Excel update for:

• Office XP w/SP3
• Office 2003 w/SP3
• Office 2004 for Mac
• Office 2008 for Mac
• Open XML File Format Converter for Mac

For All WatchGuard Users:

While you can configure certain WatchGuard Firebox models to block Word and Excel documents, some organizations need to allow them in order to conduct business. Therefore, these patches are your best recourse. Temporarily though, you may still want to block these Office documents until you are able to install Microsoft’s patches.

If you want to block Word, Excel, and Works documents, follow the links below for video instructions on using your Firebox proxy’s content blocking features to block .doc and .xls files by their file extensions:

• Firebox X Edge running 10.x
  • How do I block files with the FTP proxy?
  • How do I block files with the HTTP proxy?
  • How do I block files with the POP3 proxy?
  • How do I block files with the SMTP proxy
• Firebox X Core and X Peak running Fireware 10.x
  • How do I block files with the FTP proxy?
  • How do I block files with the HTTP proxy?
  • How do I block files with the POP3 proxy?
  • How do I block files with the SMTP proxy?

Status:

Microsoft has released Office updates to fix these vulnerabilities.

References:

• MS Security Bulletin MS10-056
• MS Security Bulletin MS10-057

This alert was researched and written by Corey Nachreiner, CISSP.