Microsoft Defender for Endpoint: Hardening Workstations with Attack Surface Reduction (ASR)
Configuring ASR rules to block executable content from email, prevent Office child processes, and stop credential stealing from LSASS.
What Are Attack Surface Reduction (ASR) Rules?
ASR rules are built-in Windows kernel and Defender controls that prevent common malware exploitation techniques before they can execute. They target typical attack chains like macro-initiated PowerShell downloads and unauthorized process memory reading.
The High-Priority ASR Rules Every Enterprise Needs
Essential rules include: 'Block executable content from email client and webmail', 'Block Office applications from creating child processes', 'Block credential stealing from the Windows local security authority subsystem (lsass.exe)', and 'Block untrusted and unsigned processes that run from USB'.
Deployment Strategy: Audit Mode to Block Mode
Enabling ASR in Block mode without telemetry testing can disrupt legitimate internal engineering scripts. AVENTIQ recommends deploying all rules in Audit mode for 30 days, reviewing event IDs 1121 and 1122 in Advanced Hunting, creating exclusions, and then transitioning to Block mode.
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