Suspicious Spoofed Inbound Email With Failed Authentication and Anonymous Internal Sender (via m365)

ATT&CK techniques

Initial Access

Recon
Resource Dev
Initial Access
- T1566.002Spearphishing Link
Execution
Persistence
Priv Esc
Defense Evasion
Cred Access
Discovery
Lateral Movement
Collection
C2
Exfiltration
Impact

What it detects

This rule detects inbound messages that fail SPF, DKIM, and composite authentication yet are marked as internal organization senders while authenticating anonymously. This combination reflects the routing and misconfiguration abuse used by phishing actors to spoof trusted internal domains and bypass tenant protections. Detecting the mismatch between claimed internal origin and failed authentication surfaces domain-spoofing phishing that would otherwise appear trustworthy to recipients.

Reporting behind it

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AWS CloudTrail SSM SendCommand Successful Execution for Instance

Suspicious Spoofed Inbound Email With Failed Authentication and Anonymous Internal Sender (via m365)

Pivot detection · T1566.002 · 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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