EIDCA-008: Legacy Authentication Blocking via CA
- Platform
- Entra ID / M365
- Category
- Entra ID Conditional Access
- Severity
- Critical
- Zero Trust pillar
- Identity (weight 3)
- Golden fixtures
- 3
- Branch coverage
- Observed: fixtures prove the verdicts they exercise
- Provenance
- baseline
What it checks
Legacy authentication protocols such as IMAP, POP3, SMTP, and ActiveSync do not support modern authentication or MFA, making them a primary attack vector for password spray and brute-force attacks. Blocking legacy authentication through Conditional Access is essential to prevent these protocols from bypassing MFA controls.
Recommended value
All legacy authentication protocols blocked via Conditional Access for all users
Remediation
Create a Conditional Access policy targeting all users and all cloud applications with the client apps condition set to Exchange ActiveSync clients and other clients, then set the grant control to block access. Verify the policy is in enabled state and monitor sign-in logs for any remaining legacy authentication attempts. Coordinate with application owners to migrate any remaining legacy protocol dependencies to modern authentication.
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
- CISA SCuBA
- MS.AAD.1.1v1
- NIST SP 800-53
- IA-2, AC-17(2)
- CIS M365 Benchmark
- 5.2.2.3
- MITRE ATT&CK
- T1078, T1110.001