Inbox Rules Creation Or Update Activity Via ExchangePowerShell Cmdlet

SIGMA detection rule by Marco Pedrinazzi (@pedrinazziM) (InTheCyber) · GPL-2.0

Detects inbox rule creation or update via ExchangePowerShell cmdlet, 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.

title: Inbox Rules Creation Or Update Activity Via ExchangePowerShell Cmdlet
id: e95a1630-e48b-41c3-b2ca-2bd6f33e1bce
related:
    - id: d3577be1-42c9-44a7-b56e-2e8de97349d3
      type: similar
    - id: 04580eed-e1d6-426b-a570-f6e64a4577f7
      type: derived
status: experimental
description: |
    Detects inbox rule creation or update via ExchangePowerShell cmdlet, 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/new-inboxrule?view=exchange-ps
    - https://learn.microsoft.com/it-it/powershell/module/exchangepowershell/set-inboxrule?view=exchange-ps
author: Marco Pedrinazzi (@pedrinazziM) (InTheCyber)
date: 2026-02-10
tags:
    - attack.stealth
    - attack.t1564.008
    - attack.exfiltration
    - attack.collection
    - attack.t1114.003
    - detection.threat-hunting
logsource:
    product: windows
    category: ps_script
    definition: 'Requirements: Script Block Logging must be enabled'
detection:
    ps_script:
        EventID: 4104
        Channel:
            - Microsoft-Windows-PowerShell/Operational
            - PowerShellCore/Operational
    selection_cmdlet:
        ScriptBlockText|contains:
            - New-InboxRule
            - Set-InboxRule
    selection_params:
        ScriptBlockText|contains:
            - DeleteMessage
            - MarkAsRead
            - MoveToFolder
            - SubjectOrBodyContainsWords
    condition: ps_script and (all of selection_*)
falsepositives:
    - Legitimate inbox rules created by users or administrators to manage email flow such as filtering, organizing, or automating email handling.
level: medium
ruletype: Sigma

[[ currentRule.title && currentRule.title.length > 60 ? currentRule.title.slice(0, 60) + '…' : currentRule.title ]]

2ff21374-0eb7-45ef-b46d-84b39254ef46

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Executable code, not a declarative rule

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