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Description

This detection is designed to identify instances where email forwarding has been enabled on mailboxes within an Office 365 environment. By monitoring for the specific operation Set-Mailbox within the o365_management_activity logs, this analytic hones in on changes made to mailbox configurations that initiate the forwarding of emails. It specifically looks for the activation of ForwardingAddress or ForwardingSmtpAddress parameters, indicating that emails are being automatically sent to another email address from the user's mailbox.

  • Type: TTP

  • Product: Splunk Enterprise, Splunk Enterprise Security, Splunk Cloud

  • Last Updated: 2024-03-26
  • Author: Patrick Bareiss, Mauricio Velazco, Splunk
  • ID: 0b6bc75c-05d1-4101-9fc3-97e706168f24

Annotations

ATT&CK

ATT&CK

ID Technique Tactic
T1114 Email Collection Collection
T1114.003 Email Forwarding Rule Collection
Kill Chain Phase
  • Exploitation
NIST
  • DE.CM
CIS20
  • CIS 10
CVE 


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`o365_management_activity` Operation=Set-Mailbox  
| eval match1=mvfind('Parameters{}.Name', "ForwardingAddress") 
| eval match2=mvfind('Parameters{}.Name', "ForwardingSmtpAddress") 
| where match1>= 0 OR match2>= 0 
| eval ForwardTo=coalesce(ForwardingAddress, ForwardingSmtpAddress) 
| search ForwardTo!=""  
| rename user_id as user 
| stats count earliest(_time) as firstTime latest(_time) as lastTime values(ForwardTo) as ForwardTo by user ObjectId 
|`security_content_ctime(firstTime)`  
|`security_content_ctime(lastTime)` 
| `o365_mailbox_email_forwarding_enabled_filter`

Macros

The SPL above uses the following Macros:

:information_source: o365_mailbox_email_forwarding_enabled_filter is a empty macro by default. It allows the user to filter out any results (false positives) without editing the SPL.

Required fields

List of fields required to use this analytic.

  • _time
  • Operation
  • Parameters{}.Name
  • src_user
  • DeliverToMailboxAndForward
  • ObjectId

How To Implement

You must install the Splunk Microsoft Office 365 Add-on and ingest Office 365 management activity events.

Known False Positives

Email forwarding may be configured for legitimate purposes, filter as needed.

Associated Analytic Story

RBA

Risk Score Impact Confidence Message
42.0 70 60 Email forwarding configured by $user$ on mailbox $ObjectId$

:information_source: The Risk Score is calculated by the following formula: Risk Score = (Impact * Confidence/100). Initial Confidence and Impact is set by the analytic author.

Reference

Test Dataset

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 | version: 1