VBA Vulnerability Makes Office Documents Dangerous

Summary:

• This vulnerability affects: Microsoft Visual Basic for Applications (VBA), which ships with all current versions of Office
• How an attacker exploits it: By tricking one of your users into opening a malicious Office document
• Impact: An attacker can potentially gain complete control of your windows computers (depending on the privileges of the user)
• What to do: Download, test, and install Microsoft’s update as soon as possible, or let Windows Automatic Update do it for you

Exposure:

According to Microsoft, Visual Basic for Applications (VBA) is “a development technology for developing client desktop packaged applications and integrating them with existing data and systems.” In more understandable terms, it’s a programming language that allows developers to make customized applications based on the Office applications. All current versions of Office ship with VBA, and the Office applications make use of it to perform certain functions.

According to this Microsoft security bulletin, VBA suffers from a memory corruption vulnerability having to do with the way it searches for ActiveX controls in a document that supports VBA. Without getting too deep into the technical details, if an attacker can lure one of your users into downloading a specially crafted Office document that supports VBA, he can exploit this flaw to execute code on that user’s computer, with that user’s privileges. If the user has local administrator privileges, that attacker gains full control of the PC. An attacker can trigger this flaw using just about any Office document, including Word, PowerPoint, and Excel documents.

Solution Path:

Microsoft has released patches to fix these vulnerabilities. You should download, test, and deploy the appropriate Office and VBA patches as soon as possible, or let Windows Automatic Update do it for you.

• Office XP
• Office 2003
• 2007 Microsoft Office System
• Microsoft Visual Basic for Applications

For All WatchGuard Users:

You can configure certain WatchGuard Firebox models to block Microsoft Office documents, such as Word, PowerPoint, and Excel documents. However, most organizations need to allow Office documents in order to conduct business. Therefore, Microsoft patches are your best recourse.

Nonetheless, if you do want to block Office documents, follow the links below for video instructions on using your Firebox proxy’s content blocking features by file extensions. Some of the file extensions you’d want to block include:

• .doc
• .docx
• .ppt
• .pptx
• .xls
• .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 patches to fix these vulnerabilities.

References:

• MS Security Bulletin MS10-031

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