O365 New Email Forwarding Rule Enabled

name: O365 New Email Forwarding Rule Enabled
id: ac7c4d0a-06a3-4278-aa59-88a5e537f981
version: 8
date: '2026-03-10'
author: Mauricio Velazco, Splunk
data_source: []
type: TTP
status: production
description: The following analytic identifies the creation of new email forwarding rules in an Office 365 environment via the UpdateInboxRules operation. It leverages Office 365 management activity events to detect rules that forward emails to external recipients by examining the OperationProperties for specific forwarding actions. This activity is significant as it may indicate unauthorized email redirection, potentially leading to data exfiltration. If confirmed malicious, attackers could intercept sensitive communications, leading to data breaches and information leakage.
search: "`o365_management_activity` Workload=Exchange Operation=UpdateInboxRules | eval match1=mvfind('OperationProperties{}.Value', \"ForwardToRecipientsAction\") | eval match2=mvfind('OperationProperties{}.Value', \"ForwardAsAttachmentToRecipientsAction\") | eval match3=mvfind('OperationProperties{}.Value', \"RedirectToRecipientsAction\") | eval index = mvfind('OperationProperties{}.Name', \"ServerRule\") | where match1>=0 OR match2>= 0 OR match3>= 0 | eval ServerRule = mvindex('OperationProperties{}.Value',index-1) | spath input=ServerRule path=Actions{}.Recipients{}.Values{}.Value output=valueExtracted | mvexpand valueExtracted | search valueExtracted=\"*@*.*\" | eval ForwardTo=if(match(valueExtracted,\"^[^@]+@[^@]+\\\\.[^@]+$\"), valueExtracted, null) | dedup ForwardTo | where isnotnull(ForwardTo) | fillnull | stats count min(_time) as firstTime max(_time) as lastTime values(Name) as Name by signature dest user src vendor_account vendor_product ForwardTo | `security_content_ctime(firstTime)` | `security_content_ctime(lastTime)` | `o365_new_email_forwarding_rule_enabled_filter`"
how_to_implement: You must install the Splunk Microsoft Office 365 Add-on and ingest Office 365 management activity events.
known_false_positives: Users may create email forwarding rules for legitimate purposes. Filter as needed.
references:
    - https://attack.mitre.org/techniques/T1114/003/
drilldown_searches:
    - name: View the detection results for - "$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: $info_max_time$
rba:
    message: A forwarding email inbox rule was created for $user$
    risk_objects:
        - field: user
          type: user
          score: 50
    threat_objects: []
tags:
    analytic_story:
        - Office 365 Collection Techniques
    asset_type: O365 Tenant
    mitre_attack_id:
        - T1114.003
    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/T1114.003/o365_email_forwarding_rule_created/o365_email_forwarding_rule_created.log
          sourcetype: o365:management:activity
          source: o365