EIDAUTH-015: Legacy Authentication Protocol Usage
- Platform
- Entra ID / M365
- Category
- Entra ID Authentication Methods & MFA
- Severity
- High
- 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 including POP3, IMAP4, SMTP AUTH, and Exchange ActiveSync Basic do not support modern authentication or MFA, allowing attackers to bypass MFA entirely using stolen credentials. These protocols transmit credentials in ways that are susceptible to interception and are the primary vector for password spray attacks against Microsoft 365 tenants. All legacy authentication should be blocked via Conditional Access policies.
Recommended value
All legacy authentication protocols blocked via Conditional Access with no active usage detected in sign-in logs
Remediation
Review legacy authentication usage in Entra ID > Monitoring > Sign-in logs > Filter by client app (legacy protocols). Create a Conditional Access policy to block legacy authentication for all users and all cloud apps. Monitor for blocked sign-in attempts and work with affected users to migrate to modern authentication clients.
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 |
| no-data | 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