Enable Attack Surface Reduction Rules
Implementation Effort: High
This requires IT and Security Operations teams to configure policies via Intune, Group Policy, or PowerShell, and potentially monitor and tune rules over time.
User Impact: Low
These rules operate at the system level and do not require end-user interaction or awareness unless the "Warn" mode is used.
Overview
Attack Surface Reduction (ASR) rules are a set of configurable policies in Microsoft Defender for Endpoint that help block behaviors commonly used by malware, such as launching executable content from email or Office files, or using scripts to download and run code. These rules can be enforced in different modes: Block, Audit, Warn, or Disabled. They are especially effective in reducing exposure to fileless and script-based attacks.
ASR rules can be deployed using Microsoft Intune, Group Policy, Configuration Manager, or PowerShell. While a Windows E5 license provides advanced monitoring and analytics through Microsoft Defender XDR, organizations with E3 or Pro licenses can still use Event Viewer or custom monitoring solutions.
Failing to implement ASR rules leaves endpoints vulnerable to common attack vectors like malicious macros, script-based attacks, and DLL injection techniques. Enabling ASR supports the Zero Trust principle of "Assume Breach" by proactively reducing the attack surface and limiting the ways malware can execute or spread.