M365EXO-003: Anti-malware policy audit
- Platform
- Entra ID / M365
- Category
- Advanced Threat Protection
- Severity
- High
- Zero Trust pillar
- Applications & Workloads (weight 2)
- Golden fixtures
- 3
- Branch coverage
- Observed: fixtures prove the verdicts they exercise
- Provenance
- baseline
What it checks
Anti-malware policies in Exchange Online scan email attachments for known malware, viruses, and malicious content before delivery. Default anti-malware settings may not block all dangerous file types, and certain attachment types commonly used in attacks such as executables and scripts may pass through without filtering. A comprehensive anti-malware policy with common attachment type filtering is essential to prevent malware delivery via email.
Recommended value
Common attachment types filter enabled blocking executable and script file types; zero-hour auto purge enabled; admin notifications enabled for malware detection
Remediation
Review the anti-malware policy and enable the common attachments filter to block dangerous file types including exe, vbs, js, ps1, bat, cmd, and other executable formats. Enable zero-hour auto purge (ZAP) to retroactively remove malware detected in already-delivered messages. Configure administrator notifications to alert the security team when malware is detected and verify that the policy is applied to all recipients in the organization.
Fixture-proven verdicts
Every verdict below is proven by a golden fixture in the module's gating test suite. This table derives from the last green run; it cannot be edited by hand.
| Scenario | Expected verdict |
|---|---|
| clean | PASS |
| known-bad | WARN |
| throttled | Not Assessed |
Framework mappings
- NIST SP 800-53
- SI-3
- CIS M365 Benchmark
- 2.1.3
- MITRE ATT&CK
- T1204