M365EXO-011: OAuth/SMTP AUTH per-mailbox audit
- Plataforma
- Entra ID / M365
- Categoría
- Advanced Threat Protection
- Severidad
- High
- Pilar de Zero Trust
- Applications & Workloads (peso 2)
- Fixtures de referencia
- 3
- Cobertura de ramas
- Observada: los fixtures prueban los veredictos que ejercitan
- Procedencia
- baseline
Qué comprueba
Legacy authentication protocols such as SMTP AUTH allow mailbox authentication using only username and password, bypassing multi-factor authentication and Conditional Access controls. Attackers who obtain mailbox credentials through phishing or password spraying can use SMTP AUTH to access email without triggering MFA challenges. Disabling SMTP AUTH and legacy OAuth flows on mailboxes that do not require them closes a significant authentication bypass vector.
Valor recomendado
SMTP AUTH disabled organization-wide with per-mailbox exceptions only for documented service accounts; legacy OAuth disabled
Remediación
Disable SMTP AUTH at the organization level using Set-TransportConfig and then selectively enable it only for specific service account mailboxes that require it for application integration. Audit all mailboxes with SMTP AUTH enabled to verify there is a documented business justification and that the credentials are managed securely. Monitor sign-in logs for SMTP AUTH usage to detect potential credential abuse and plan migration of legacy applications to modern authentication methods.
Veredictos probados con fixtures
Cada veredicto de esta tabla está probado por un fixture de referencia en la suite de pruebas que valida el módulo. La tabla se deriva de la última ejecución en verde; no puede editarse a mano.
| Escenario | Veredicto esperado |
|---|---|
| clean | PASS |
| known-bad | FAIL |
| throttled | Not Assessed |
Mapeos a marcos de referencia
- CISA SCuBA
- MS.EXO.5.1v1
- NIST SP 800-53
- IA-2
- CIS M365 Benchmark
- 1.1.16
- MITRE ATT&CK
- T1078