Detection: O365 New Email Forwarding Rule Created

Updated Date: 2024-11-14 ID: 68469fd0-1315-44ba-b7e4-e92847bb76d6 Author: Mauricio Velazco, Splunk Type: TTP Product: Splunk Enterprise Security

Description

The following analytic identifies the creation of new email forwarding 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 like ForwardTo, ForwardAsAttachmentTo, and RedirectTo. This activity is significant as unauthorized email forwarding can lead to data exfiltration and unauthorized access to sensitive information. If confirmed malicious, attackers could intercept and redirect emails, potentially compromising confidential communications and leading to data breaches.

 1`o365_management_activity` (Operation=New-InboxRule OR Operation=set-InboxRule) 
 2| eval match1=mvfind('Parameters{}.Name', "ForwardTo") 
 3| eval match2=mvfind('Parameters{}.Name', "ForwardAsAttachmentTo") 
 4| eval match3=mvfind('Parameters{}.Name', "RedirectTo") 
 5| where match1>= 0 OR match2>= 0 OR match3>= 0 
 6| eval ForwardTo=coalesce(ForwardTo, ForwardAsAttachmentTo, RedirectTo) 
 7| stats count min(_time) as firstTime max(_time) as lastTime values(Name) as Name by user Operation ForwardTo 
 8| `security_content_ctime(firstTime)` 
 9| `security_content_ctime(lastTime)` 
10| `o365_new_email_forwarding_rule_created_filter`

Data Source

No data sources specified for this detection.

Macros Used

Name Value
o365_management_activity sourcetype=o365:management:activity
o365_new_email_forwarding_rule_created_filter search *
o365_new_email_forwarding_rule_created_filter is an empty macro by default. It allows the user to filter out any results (false positives) without editing the SPL.

Annotations

- MITRE ATT&CK
+ Kill Chain Phases
+ NIST
+ CIS
- Threat Actors
ID Technique Tactic
T1114 Email Collection Collection
T1114.003 Email Forwarding Rule Collection
Exploitation
DE.CM
CIS 10

Default Configuration

This detection is configured by default in Splunk Enterprise Security to run with the following settings:

Setting Value
Disabled true
Cron Schedule 0 * * * *
Earliest Time -70m@m
Latest Time -10m@m
Schedule Window auto
Creates Notable Yes
Rule Title %name%
Rule Description %description%
Notable Event Fields user, dest
Creates Risk Event True
This configuration file applies to all detections of type TTP. These detections will use Risk Based Alerting and generate Notable Events.

Implementation

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.

Associated Analytic Story

Risk Based Analytics (RBA)

Risk Message:

A forwarding email inbox rule was created for $user$

Risk Object Risk Object Type Risk Score Threat Objects
user user 42 No Threat Objects

References

Detection Testing

Test Type Status Dataset Source Sourcetype
Validation ✅ Passing N/A N/A N/A
Unit ✅ Passing Dataset o365 o365:management:activity
Integration ✅ Passing Dataset o365 o365:management:activity

Replay any dataset to Splunk Enterprise by using our replay.py tool or the UI. Alternatively you can replay a dataset into a Splunk Attack Range

Source: GitHub | Version: 4