A Major Shift in Office Security: Microsoft to Retire Application Guard
Microsoft is making a significant change to its security lineup by announcing the deprecation of Microsoft Defender Application Guard for Office. This feature, which provided an extra layer of protection by opening untrusted documents in an isolated, virtualized container, will be phased out. For IT administrators and security-conscious users, this change necessitates a shift in strategy for defending against malicious Word, Excel, and PowerPoint files.
While the removal of a security feature may sound alarming, Microsoft is not leaving users unprotected. Instead, the company is consolidating its security approach, steering users toward a more integrated and robust solution: Microsoft Defender for Endpoint’s Attack Surface Reduction (ASR) rules, complemented by the existing Protected View functionality.
What Was Application Guard and Why Is It Changing?
Application Guard for Office was a powerful tool designed to neutralize threats embedded in documents. When you opened a file from an untrusted source, such as an email attachment or an internet download, Application Guard would launch it in a secure, hardware-isolated “sandbox.” This sandbox environment effectively prevented any malicious code within the document from accessing your computer’s data, network, or core operating system.
The primary reason for this change is to streamline security management. Rather than relying on a separate containerization technology, Microsoft is integrating this protection directly into its broader endpoint security platform. This move simplifies the security stack for administrators and aligns document protection with the same advanced tools used to protect the rest of the operating system.
The New Standard: Attack Surface Reduction (ASR) Rules
The designated replacement for Application Guard’s functionality is a set of powerful policies known as Attack Surface Reduction (ASR) rules. These rules are a core component of Microsoft Defender for Endpoint and are designed to block common behaviors and techniques used by malware to launch attacks.
Instead of isolating the entire document, ASR rules target the specific malicious actions an attacker might attempt. Key ASR rules relevant for Office security include:
- Blocking Office applications from creating executable content.
- Preventing Office applications from injecting code into other processes.
- Blocking Win32 API calls from Office macros.
- Preventing Office communication applications from creating child processes.
By focusing on these high-risk behaviors, ASR rules can stop an attack at its source without the performance overhead of virtualization. This approach is both more efficient and more comprehensive, as it is part of a unified security platform that correlates signals from across your entire digital environment.
It’s also important to remember that Protected View will continue to be the first line of defense. This built-in Office feature opens documents from potentially unsafe locations in a restricted, read-only mode, disabling macros, editing, and other active content until you explicitly trust the document.
Actionable Steps: How to Prepare for the Transition
With Application Guard for Office being retired, IT administrators must take proactive steps to ensure their organization’s security posture remains strong. Here is a recommended checklist to guide your transition:
Audit Your Current Configuration: The first step is to understand if your organization currently uses and relies on Application Guard for Office. This feature was primarily available for users with Microsoft 365 E5 or E5 Security licenses.
Deploy and Configure ASR Rules: If you haven’t already, begin planning the deployment of Attack Surface Reduction rules. Microsoft recommends starting in “audit mode,” which allows you to see which rules would be triggered without actually blocking any actions. This is a critical step to identify potential impacts on legitimate business workflows before full enforcement.
Prioritize Key Office-Related Rules: Focus on implementing the ASR rules specifically designed to mitigate threats from Office applications. Review Microsoft’s official documentation to understand which rules provide the most relevant protection for your environment.
Educate Your Users: Reinforce the importance of security best practices. Remind users to be cautious with email attachments and downloads. Crucially, instruct them never to disable Protected View or enable content from an untrusted document unless they are absolutely certain of its origin and safety.
By transitioning from Application Guard to a robust ASR ruleset, organizations can maintain, and even enhance, their protection against document-based threats in a more integrated and manageable way. This change reflects the evolving cybersecurity landscape, moving from isolated solutions toward unified, behavior-based threat prevention.
Source: https://www.bleepingcomputer.com/news/microsoft/microsoft-removing-defender-application-guard-from-office/
