Malicious OAuth Application Granted Full Mailbox and EWS Permissions (via m365)

ATT&CK techniques

Persistence → Cred Access

Recon
Resource Dev
Initial Access
Execution
Persistence
- T1098.002Additional Email Delegate Permissions
Priv Esc
- T1098.002Additional Email Delegate Permissions
Defense Evasion
Cred Access
- T1528Steal Application Access Token
Discovery
Lateral Movement
Collection
C2
Exfiltration
Impact

What it detects

This rule detects OAuth application permission grants for high privilege mailbox scopes such as full_access_as_app EWS.AccessAsUser.All and ApplicationImpersonation. Midnight Blizzard granted these permissions to attacker-controlled applications to access mailboxes across the tenant.

Reporting behind it

Related detections9 linkedT1528 — drag to rearrange

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Suspicious Salesforce Connected App OAuth Authorization from VPN Egress

Suspicious M365 Device Code Authentication Flow via m365

Malicious OAuth Application Granted Full Mailbox and EWS Permissions (via m365)

Pivot detection · T1528 · 9 related

Detection content is published as a reviewed draft. Tune thresholds and exclusions against your own telemetry before enabling this rule for alerting.

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