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Microsoft Patch Tuesday Roundup - November 2010 - "Stuck In The Mud" Edition

Balancing Risk

Security continues to be a balance between providing users with features and mitigating risk. . Client-side vulnerabilities seem to be the hole that many of us are stuck spinning our wheels in.

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This month Microsoft fixed a buffer overflow vulnerability in Word that resulted from the processing of RTF documents in security bulletin MS10-87. This has already received some immediate attention, primarily because Outlook can be an attack vector due to the preview pane automatically displaying the contents of file attachments. At some point, you have to ask yourself "How important is it for the users to use the preview pane in Microsoft Outlook?" Viewing emails in plain text still allows users to view so-called "rich content" as attachments, forcing them to open an attachment, rather than having an infection occur if the email is previewed and automatically rendering the contents of the attachment (I've always been a huge fan of plain text email, stemming from my early email days of using Pine). It still allows you to communicate effectively via email, but removes a large percentage of potential attack vectors including images, HTML/JavaScript and attachments (e.g., Microsoft Office documents).

Even if you are patched...

There are still users who will be tricked, or will open any attachment just out of sheer curiosity. Let’s face it, it is likely part of their job to open documents (my favorite example is HR personnel, forced to open resumes in PDF and Word formats). Being up-to-date on the latest software is important, however VBScript macros embedded inside of Office documents can often lead to code execution just as easily as a software vulnerability. This month's patch update from Microsoft fixes seven vulnerabilities in Microsoft Office, but we shouldn't get hung up on the vulnerabilities themselves. We need to prevent the attacks from happening in the first place.

Getting to the bottom of the problem

Organizations need to look beyond patches and software security and define the real problem: users are receiving documents that allow code execution. Whether this stems from a software vulnerability or an embedded macro, the result is the same and attackers are bypassing the security mechanisms put in place. There are a few different ways to prevent this attack vector and a combination of the following approaches will likely be the most effective:

  • Manage the configuration of the client, hardening the operating system and applications
  • Read emails in plain text
  • Disallow certain attachment types
  • Scan documents with antivirus software both on the gateways and on the client system
  • Disable features such as Office document macros
  • Implement a security awareness program for end users

All of these measures go a long way to frustrate attackers. While you may never be able to stop a determined attacker 100% of the time, you can make the attacker's life more difficult. Another defensive measure that shows great promise is tracking where processes are connecting. For example, why should a Microsoft Word program be making an outbound TCP connection to the Internet? This behavior is anomalous and needs to be monitored and flagged as suspicious (or even blocked) by the operating system.

To further aid in your efforts to evaluate the dangers of the Microsoft Patch Tuesday mayhem, Tenable's Research team has published plugins for each of the security bulletins issued this month:

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