O365 Email Transport Rule Changed

name: O365 Email Transport Rule Changed
id: 11ebb7c2-46bd-41c9-81e1-d0b4b34583a2
version: 5
date: '2026-03-10'
author: Steven Dick
status: production
type: Anomaly
description: The following analytic identifies when a user with sufficient access to Exchange Online alters the mail flow/transport rule configuration of the organization. Transport rules are a set of rules that can be used by attackers to modify or delete emails based on specific conditions, this activity could indicate an attacker hiding or exfiltrated data.
data_source:
    - Office 365 Universal Audit Log
search: |-
    `o365_management_activity` Workload=Exchange AND Operation IN ("Set-*","Disable-*","New-*","Remove-*") AND Operation="*TransportRule"
    | eval object_name = case('Parameters{}.Name'=="Name",mvindex('Parameters{}.Value',mvfind('Parameters{}.Name',"^Name$")),true(),ObjectId), object_id = case('Parameters{}.Name'=="Identity",mvindex('Parameters{}.Value',mvfind('Parameters{}.Name',"^Identity$")),true(),Id)
    | stats values(object_name) as object_name, min(_time) as firstTime, max(_time) as lastTime, count by object_id, UserId, Operation, signature
    | rename UserId as user
    | `security_content_ctime(firstTime)`
    | `security_content_ctime(lastTime)`
    | `o365_email_transport_rule_changed_filter`
how_to_implement: You must install the Splunk Microsoft Office 365 Add-on and ingest Office 365 management activity events.
known_false_positives: Legitimate administrative changes for business needs.
references:
    - https://attack.mitre.org/techniques/T1114/003/
    - https://cardinalops.com/blog/cardinalops-contributes-new-mitre-attck-techniques-related-to-abuse-of-mail-transport-rules/
    - https://www.microsoft.com/en-us/security/blog/2022/09/22/malicious-OAuth-applications-used-to-compromise-email-servers-and-spread-spam/
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 changes by $user$
      search: '`o365_management_activity` Workload=Exchange AND Operation IN ("Set-*","Disable-*","New-*","Remove-*") AND Operation="*Transport*" UserId=$user$'
      earliest_offset: $info_min_time$
      latest_offset: $info_max_time$
rba:
    message: The user [$user$] altered the exchange transport rule id [$object_name$]
    risk_objects:
        - field: user
          type: user
          score: 20
    threat_objects:
        - field: object_id
          type: signature
        - field: object_name
          type: signature
tags:
    analytic_story:
        - Data Exfiltration
        - Office 365 Account Takeover
    asset_type: O365 Tenant
    mitre_attack_id:
        - T1114.003
        - T1564.008
    product:
        - Splunk Enterprise
        - Splunk Enterprise Security
        - Splunk Cloud
    security_domain: threat
tests:
    - name: True Positive Test
      attack_data:
        - data: https://media.githubusercontent.com/media/splunk/attack_data/master/datasets/attack_techniques/T1114.003/transport_rule_change/transport_rule_change.log
          source: o365
          sourcetype: o365:management:activity