sigmamediumHunting

Inbox Rules Creation Or Update Activity in O365

Detects inbox rule creation or update via O365 Audit logs, a technique commonly observed in Business Email Compromise (BEC) attacks to hide emails. The usage of inbox rules can be a sign of a compromised mailbox, where an attacker is attempting to evade detections by suppressing or redirecting incoming emails. Analysts should review these rules in context, validate whether they reflect normal user behavior, and correlate with other indicators such as unusual login activity or recent mailbox rule modifications.

MITRE ATT&CK

T1564.008 T1114.003

defense-evasionexfiltrationcollection

Detection Query

selection:
  Operation:
    - New-InboxRule
    - Set-InboxRule
  Parameters|contains:
    - DeleteMessage
    - MarkAsRead
    - MoveToFolder
    - SubjectOrBodyContainsWords
condition: selection

Author

Marco Pedrinazzi (@pedrinazziM) (InTheCyber)

Created

2026-01-09

Data Sources

m365audit

Platforms

m365

References

Tags

attack.defense-evasionattack.t1564.008attack.exfiltrationattack.collectionattack.t1114.003detection.threat-hunting

Raw Content

title: Inbox Rules Creation Or Update Activity in O365
id: d3577be1-42c9-44a7-b56e-2e8de97349d3
status: experimental
description: |
    Detects inbox rule creation or update via O365 Audit logs, a technique commonly observed in Business Email Compromise (BEC) attacks to hide emails.
    The usage of inbox rules can be a sign of a compromised mailbox, where an attacker is attempting to evade detections by suppressing or redirecting incoming emails.
    Analysts should review these rules in context, validate whether they reflect normal user behavior, and correlate with other indicators such as unusual login activity or recent mailbox rule modifications.
references:
    - https://redcanary.com/threat-detection-report/techniques/email-hiding-rules/
    - https://learn.microsoft.com/it-it/powershell/module/exchangepowershell/set-inboxrule?view=exchange-ps
    - https://learn.microsoft.com/it-it/powershell/module/exchangepowershell/new-inboxrule?view=exchange-ps
author: Marco Pedrinazzi (@pedrinazziM) (InTheCyber)
date: 2026-01-09
tags:
    - attack.defense-evasion
    - attack.t1564.008
    - attack.exfiltration
    - attack.collection
    - attack.t1114.003
    - detection.threat-hunting
logsource:
    service: audit
    product: m365
    definition: "Requirements: The 'Parameters' field is a list of dict. A correct mapping to the 'Value' field inside is recommended to avoid greedy search"
detection:
    selection:
        Operation:
            - 'New-InboxRule'
            - 'Set-InboxRule'
        Parameters|contains:
            - 'DeleteMessage'
            - 'MarkAsRead'
            - 'MoveToFolder'
            - 'SubjectOrBodyContainsWords'
    condition: selection
falsepositives:
    - Legitimate inbox rules created by users or administrators to manage email flow such as filtering, organizing, or automating email handling.
level: medium