Suspicious Inbox Rule Creation That Deletes Incoming Mail via Exchange (via m365)

ATT&CK techniques

Defense Evasion → Collection

Recon
Resource Dev
Initial Access
Execution
Persistence
Priv Esc
Defense Evasion
- T1564.008Email Hiding Rules
Cred Access
Discovery
Lateral Movement
Collection
- T1114.003Email Forwarding Rule
C2
Exfiltration
Impact

What it detects

This rule detects the creation or modification of Exchange inbox rules that silently delete or hide incoming mail, a technique used in the back-to-school email account compromise campaign reported by Red Canary. Adversaries who take over an educational mailbox create hidden rules with obscure names to auto-delete replies and warnings while they conduct internal spearphishing, and this activity should be reviewed to catch account takeover before it spreads.

Reporting behind it

Related detections9 linkedT1564.008 — drag to rearrange

Malicious Inbox Rule Hiding Security Mail to RSS Feeds via M365 (via m365)

Malicious Exchange Inbox Rule Hiding Direct Deposit and Bank Emails via Payroll Pirate Compromise (via m365)

Detect Email Forwarding/Redirecting via Exchange PowerShell InboxRule Cmdlets on Windows

Windows PowerShell: New-InboxRule/Set-InboxRule Script Block Activity

Microsoft 365 Audit Logs: Inbox Rule Creation or Update with Email Hiding Actions

O365 Mail Forwarding and Redirecting Rule Changes

Suspicious Exchange Inbox Forwarding Rule Creation via M365 (via m365)

Suspicious Inbox Rule Hiding Mail to Deleted Items via M365 Exchange

Suspicious Mailbox Forwarding Rule Creation Following AiTM Phishing

Suspicious Inbox Rule Creation That Deletes Incoming Mail via Exchange (via m365)

Pivot detection · T1564.008 · 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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