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Description

This detection aims to identify instances where new email forwarding rules are created through the UpdateInboxRules operation within an Office 365 environment. Despite the operation name suggesting an update, this specific scenario involves the addition of new rules that direct emails to external recipients, captured under the ForwardToRecipientsAction. The analytic examines the OperationProperties to extract and validate forwarding addresses, ensuring they adhere to the expected email format.

  • Type: TTP

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

  • Last Updated: 2024-03-28
  • Author: Mauricio Velazco, Splunk
  • ID: ac7c4d0a-06a3-4278-aa59-88a5e537f981

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` 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) 
| stats count min(_time) as firstTime max(_time) as lastTime values(Name) as Name by user Operation ForwardTo 
| `security_content_ctime(firstTime)` 
| `security_content_ctime(lastTime)` 
| `o365_new_email_forwarding_rule_enabled_filter`

Macros

The SPL above uses the following Macros:

:information_source: o365_new_email_forwarding_rule_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
  • Actions
  • Name
  • user

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.

Associated Analytic Story

RBA

Risk Score Impact Confidence Message
42.0 70 60 A forwarding email inbox rule was created for $user$

: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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