Attack Surface Reduction Rules
Understanding the Concept
Attack Surface Reduction (ASR) rules are policies that block or audit behaviors commonly used by malware and attacks. They target specific attack techniques like Office macro abuse, script-based attacks, credential stealing, and suspicious process behaviors.
ASR rules can run in three modes: Block (prevent the behavior), Audit (log but allow), and Warn (show warning to user). Best practice is to start in Audit mode, analyze the impact, then move to Block.
Key ASR rules include blocking Office apps from creating child processes, blocking execution of potentially obfuscated scripts, blocking credential stealing from LSASS, and blocking untrusted USB processes.
Key Points
- ASR rules block common attack techniques at the endpoint
- Three modes: Block, Audit, Warn
- Best practice: Audit first, then Block
- Key rules: Office macro blocking, script protection, credential theft prevention
- Deployed via Intune, Group Policy, or PowerShell
- ASR rule exclusions for legitimate business processes
Why This Matters in Real Organizations
ASR rules prevent attacks before they execute, reducing the attack surface by blocking the most common exploitation techniques. Organizations using ASR rules report a 50% reduction in endpoint compromises.
Common Mistakes to Avoid
Interview Tips
- Explain how ASR rules differ from traditional antivirus
- Discuss your approach to rolling out ASR rules safely
Exam Tips (SC-200)
- Know the key ASR rules and what each prevents
- Understand the three enforcement modes
- Know how to deploy ASR rules via Intune and GP
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