Introduction
In today’s evolving threat landscape, cybercriminals continuously exploit vulnerabilities in systems and applications. Attack Surface Reduction (ASR) rules help mitigate these risks by limiting the ways malware and threat actors can infiltrate an organization. By enforcing strict policies on script execution, Office macros, and other attack vectors, ASR rules reduce exposure to common exploits. With businesses relying on digital tools more than ever, implementing ASR is a crucial step in strengthening security posture and minimizing the risk of breaches. This proactive approach helps organizations stay ahead of cyber threats while maintaining operational efficiency.
The Urgency of Verifying ASR Rule Configuration
There are multiple ways to deploy ASR rules, including Microsoft Intune, SCCM, and PowerShell scripts. While configuring ASR is an important step, I won’t dive into the setup process in this post, as many other excellent resources already cover it in depth. If you’re looking for a detailed guide on deploying ASR rules, check out these great articles:
https://call4cloud.nl/asr-rules-explanined-automate-with-powershell/
https://jeffreyappel.nl/microsoft-defender-for-endpoint-series-attack-surface-reduction-and-additional-protection-part4b/
Instead, I want to focus on why ASR rules need to be monitored and verified on the endpoints themselves. Simply enabling ASR rules via Microsoft Intune or another deployment method isn’t enough—you can’t blindly trust that policies have applied correctly. Various factors, such as misconfigurations, conflicts with existing settings, or failed deployments, can prevent ASR rules from being enforced on devices. Many of you probably are familiar with these kind of misassumptions. Without proper auditing and testing, you might assume your systems are protected when, in reality, critical rules could be missing or inactive.
What is the “ASR Rule Inspector” and how does it work?
I designed this Powershell script because I sometimes questioned whether everything was actually applied correctly and because I wanted to have a simple overview of what is (or not) applied and with the assigned value.
I couldn’t a fine overview where you could easily read which ASR rules are (not) configured and which ones might not been configured on the device. The script will check the following:
- Configured ASR Rules and which ones are missing
- Exclusions
- Controlled Folder Access (Protected Folders and Allowed Apps)
Conclusion
Configuring ASR rules is one thing, but verifying their actual enforcement is what truly matters. Policies can fail to apply, and assumptions about security can lead to blind spots. By checking the actual values on the device, you ensure that ASR rules are doing what they’re supposed to.