M365EXO-035: No IP allow list in connection filter (MS.EXO.12.1)
- 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
SCuBA MS.EXO.12.1 recommends that IP allow lists not be created. Addresses on the connection filter allow list bypass spam filtering, SPF, DKIM, DMARC, and FROM-address enforcement. Any entry on this list is a hole through which an attacker who can send from that address can deliver mail that skips all inbound security controls.
Recommended value
Connection filter policy IPAllowList empty for all policies
Remediation
Edit the connection filter policy and remove all entries from the allowed IP address list so no senders bypass spam filtering and authentication checks. If a sender must be allowed to avoid false positives, prefer a narrowly scoped allowed-sender entry over an IP allow list. Verify no custom connection filter policy reintroduces allow-list entries.
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 | FAIL |
| throttled | Not Assessed |
Framework mappings
- NIST SP 800-53
- SC-7, SI-8
- CIS M365 Benchmark
- 2.1.12
- MITRE ATT&CK
- T1566.001