O365 Email Transport Rule Changed

name: O365 Email Transport Rule Changed
id: 11ebb7c2-46bd-41c9-81e1-d0b4b34583a2
version: 7
creation_date: '2025-01-15'
modification_date: '2026-05-13'
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/
intermediate_findings:
    entities:
        - field: user
          type: user
          score: 20
          message: The user [$user$] altered the exchange transport rule id [$object_name$]
threat_objects:
    - field: object_id
      type: signature
    - field: object_name
      type: signature
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
category: cloud
security_domain: threat