Troubleshooting Microsoft 365 Defender Attack Surface Reduction (ASR) False Positives

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Understanding Microsoft 365 Defender Attack Surface Reduction (ASR) False Positives

Deploying ASR rules in your Windows endpoints can help bolster security, but they may also generate false positives. This article provides practical solutions for troubleshooting common issues.

Recommended Approach: Start with Audit Mode

Before enforcing new ASR rules, it’s crucial to deploy them in Audit mode for at least 30 days. This allows you to monitor their impact and adjust as needed without causing disruptions.

Identifying Legitimate Triggers with KQL

To find the triggering rule, use Advanced Hunting: DeviceEvents | where ActionType startswith ‘Asr’ | summarize by ActionType, FileName, FolderPath. This will help you identify which applications or files are causing false positives.

Exclusion Granularity and Scope

To exclude legitimate triggers from ASR rules, use full path specifications. For example:

\Program Files (x86)\Microsoft Officeoot\Office16\outlook.exe

Addressing High-Volume False Positives

For rules generating high volumes of false positives in specific applications, consider creating per-rule exclusions instead of disabling the rule entirely.

Utilizing Warn Mode for User Override

Use Warn mode for high-impact rules to allow informed user override during initial enforcement. This ensures that legitimate activities are not unintentionally blocked while you fine-tune your ASR rule configuration.

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