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Description

The following analytic monitors for the creation of new mail flow rules in Office 365 that could potentially redirect or copy emails to unauthorized or external addresses. This analytic works by querying the Office 365 Management Activity logs for any operation tagged as "New-TransportRule". It specifically looks for parameters indicative of mail forwarding actions, such as "BlindCopyTo", "CopyTo", and "RedirectMessageTo". If any of these parameters are present, indicating that a forwarding rule has been set up, the detection then captures the details of this rule, including the user ID responsible for the creation, the name of the rule, the forwarding target, and the timestamps of the rule's creation and last modification.

  • Type: TTP

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

  • Last Updated: 2024-04-10
  • Author: Mauricio Velazco, Splunk
  • ID: 289ed0a1-4c78-4a43-9321-44ea2e089c14

Annotations

ATT&CK

ATT&CK

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


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`o365_management_activity` Workload=Exchange Operation="New-TransportRule" 
| eval match1=mvfind('Parameters{}.Name', "BlindCopyTo") 
| eval match2=mvfind('Parameters{}.Name', "CopyTo") 
| eval match3=mvfind('Parameters{}.Name', "RedirectMessageTo") 
| where match1>= 0 OR match2>= 0 OR match3>=0 
| eval ForwardTo=coalesce(BlindCopyTo, CopyTo, RedirectMessageTo) 
| search ForwardTo!=""  
| rename UserId as user  
| stats count earliest(_time) as firstTime latest(_time) as lastTime by Operation, user, Name, ForwardTo  
| `security_content_ctime(firstTime)` 
| `security_content_ctime(lastTime)`   
| `o365_new_forwarding_mailflow_rule_created_filter`

Macros

The SPL above uses the following Macros:

:information_source: o365_new_forwarding_mailflow_rule_created_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
  • user
  • Name

How To Implement

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

Known False Positives

Forwarding mail flow rules may be created for legitimate reasons, filter as needed.

Associated Analytic Story

RBA

Risk Score Impact Confidence Message
42.0 70 60 A new forwarding mailflow rule was created by $user$

: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

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