O365 Email New Inbox Rule Created

name: O365 Email New Inbox Rule Created
id: 449f525a-7b42-47be-96a7-d9724e336c19
version: 4
date: '2026-03-10'
author: Steven Dick
status: production
type: Anomaly
description: The following analytic identifies the creation of new email inbox rules in an Office 365 environment. It detects events logged under New-InboxRule and Set-InboxRule operations within the o365_management_activity data source, focusing on parameters that may indicate mail forwarding, removal, or obfuscation. Inbox rule creation is a typical end-user activity however attackers also leverage this technique for multiple reasons.
data_source:
    - Office 365 Universal Audit Log
search: |-
    `o365_management_activity` Workload=Exchange AND (Operation=New-InboxRule OR Operation=Set-InboxRule) Parameters{}.Name IN (SoftDeleteMessage,DeleteMessage,ForwardTo,ForwardAsAttachmentTo,RedirectTo,MoveToFolder,CopyToFolder)
    | eval file_path = mvappend(MoveToFolder,CopyToFolder), recipient=mvappend(ForwardTo, ForwardAsAttachmentTo, RedirectTo), user = lower(UserId), signature = Operation, src = if(match(ClientIP, "^\["), ltrim(mvindex(split(ClientIP, "]:"), 0), "["), mvindex(split(ClientIP,":"),0)), desc = Name, action = 'Parameters{}.Name'

    | stats values(action) as action, values(src) as src, values(recipient) as recipient, values(file_path) as file_path, count, min(_time) as firstTime, max(_time) as lastTime by user, signature, desc
    | `security_content_ctime(firstTime)`
    | `security_content_ctime(lastTime)`
    | `o365_email_new_inbox_rule_created_filter`
how_to_implement: You must install the Splunk Microsoft Office 365 Add-on and ingest Office 365 management activity events.
known_false_positives: Users may create email rules for legitimate purposes. Filter as needed.
references:
    - https://attack.mitre.org/techniques/T1114/
    - https://www.hhs.gov/sites/default/files/help-desk-social-engineering-sector-alert-tlpclear.pdf
    - https://intelligence.abnormalsecurity.com/attack-library/threat-actor-convincingly-impersonates-employee-requesting-direct-deposit-update-in-likely-ai-generated-attack
drilldown_searches:
    - name: View the detection results for - "$user$"
      search: '%original_detection_search% | search user = "$user$"'
      earliest_offset: $info_min_time$
      latest_offset: $info_max_time$
    - name: View risk events for the last 7 days for - "$user$"
      search: '| from datamodel Risk.All_Risk | search normalized_risk_object IN ("$user$") starthoursago=168  | stats count min(_time) as firstTime max(_time) as lastTime values(search_name) as "Search Name" values(risk_message) as "Risk Message" values(analyticstories) as "Analytic Stories" values(annotations._all) as "Annotations" values(annotations.mitre_attack.mitre_tactic) as "ATT&CK Tactics" by normalized_risk_object | `security_content_ctime(firstTime)` | `security_content_ctime(lastTime)`'
      earliest_offset: $info_min_time$
      latest_offset: $info_max_time$
    - name: Investigate Inbox Rules for $user$
      search: '`o365_management_activity` Workload=Exchange AND (Operation=New-InboxRule OR Operation=Set-InboxRule) AND UserId = "$user$"'
      earliest_offset: $info_min_time$
      latest_offset: $info_max_time$
rba:
    message: A new email inbox rule was created for $user$
    risk_objects:
        - field: user
          type: user
          score: 20
    threat_objects:
        - field: desc
          type: signature
tags:
    analytic_story:
        - Office 365 Collection Techniques
    asset_type: O365 Tenant
    mitre_attack_id:
        - T1114.003
        - T1564.008
    product:
        - Splunk Enterprise
        - Splunk Enterprise Security
        - Splunk Cloud
    security_domain: audit
tests:
    - name: True Positive Test
      attack_data:
        - data: https://media.githubusercontent.com/media/splunk/attack_data/master/datasets/attack_techniques/T1114/o365_suspect_email_actions/o365_exchange_suspect_events.log
          source: o365
          sourcetype: o365:management:activity