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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.

  • Type: TTP

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

  • Last Updated: 2024-05-23
  • 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

source | version: 2