Suspicious Inbox Rule Hiding Mail to Deleted Items via M365 Exchange

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
- T1114.002Remote Email Collection
C2
Exfiltration
Impact

What it detects

This rule detects inbox rules that match on the @ character and move matching messages to the Deleted Items folder in Microsoft 365. This behavior was used in the Huntress traitorware intrusion to hide reply and alert traffic, a common business email compromise evasion technique that conceals ongoing mailbox abuse from the legitimate user.

Reporting behind it

Related detections9 linkedT1564.008 — drag to rearrange

Suspicious SCATTERED SPIDER Exchange Transport Rule Creation to Suppress Alerts (via m365)

Malicious Exchange Mailbox Export to ASPX via New-MailboxExportRequest

Suspicious Email-Hiding Inbox Rule Creation (via exchange)

Suspicious Inbox Rule Moving Mail to Junk for Concealment (via m365)

Suspicious Exchange Online Mail Flow Rule or Connector Creation via Compromised Account

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 Inbox Rule Hiding Mail to Deleted Items via M365 Exchange

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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