Eight Excel Vulnerabilities Makes Spreadsheets Risky

Severity: High

14 June, 2011

Summary:

• These vulnerabilities affect: Most current versions of Excel, which ships with Microsoft Office
• How an attacker exploits it: By enticing one of your users to open a malicious Excel document
• Impact: In the worst case, an attacker executes code on your user’s computer, gaining complete control of it
• What to do: Install Microsoft Office updates as soon as possible, or let Microsoft’s automatic update do it for you

Exposure:

As part of today’s Patch Day, Microsoft released a security bulletin describing eight vulnerabilities found in Excel — part of Microsoft Office for Windows and Mac. The flaws also affect some of the Office document viewer and converter applications

Though the eight vulnerabilities differ technically, they share the same scope and impact. If an attacker can entice one of your users into downloading and opening a maliciously crafted Excel document, he 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.

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, or let the Microsoft Automatic Update feature do it for you.

Excel update for:

• Office XP w/SP3
• Office 2003 w/SP3
• Office 2007 w/SP2
• Office 2010 32-bit
• Office 2010 64-bit

• Office 2004  for Mac
• Office 2008  for Mac
• Office for Mac 2011
• Open XML File Format Converter for Mac

• Excel Viewer
• Office Compatibility Pack for Word, Excel, and PowerPoint 2007 File Formats

For All WatchGuard Users:

While you can configure certain WatchGuard Firebox models to block Microsoft Excel documents, some organizations need to allow them in order to conduct business. Therefore, these patches are your best recourse.

If you want to block Excel documents, follow the links below for video instructions on using your Firebox proxy’s content blocking features by file extensions (.xls and .xlsx). Keep in mind, blocking files by extension blocks both malicious and legitimate documents.

• 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 MS11-045

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