O365 New Email Forwarding Rule Enabled

name: O365 New Email Forwarding Rule Enabled
id: ac7c4d0a-06a3-4278-aa59-88a5e537f981
version: 10
creation_date: '2024-04-17'
modification_date: '2026-05-13'
author: Mauricio Velazco, Splunk
status: production
type: TTP
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.
data_source: []
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/
finding:
    title: A forwarding email inbox rule was created for $user$
    entity:
        field: user
        type: user
        score: 50
analytic_story:
    - Office 365 Collection Techniques
asset_type: O365 Tenant
mitre_attack_id:
    - T1114.003
product:
    - Splunk Enterprise
    - Splunk Enterprise Security
    - Splunk Cloud
category: cloud
security_domain: audit