Detection: O365 New Email Forwarding Rule Enabled

Updated Date: 2024-05-23 ID: ac7c4d0a-06a3-4278-aa59-88a5e537f981 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 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.

 1`o365_management_activity` Workload=Exchange Operation=UpdateInboxRules  
 2| eval match1=mvfind('OperationProperties{}.Value', "ForwardToRecipientsAction") 
 3| eval match2=mvfind('OperationProperties{}.Value', "ForwardAsAttachmentToRecipientsAction") 
 4| eval match3=mvfind('OperationProperties{}.Value', "RedirectToRecipientsAction") 
 5| eval index = mvfind('OperationProperties{}.Name', "ServerRule") 
 6| where match1>= 0 OR match2>= 0 OR match3>= 0 
 7| eval ServerRule = mvindex('OperationProperties{}.Value', index-1) 
 8| spath input=ServerRule path=Actions{}.Recipients{}.Values{}.Value output=valueExtracted 
 9| mvexpand valueExtracted 
10| search valueExtracted="*@*.*" 
11| eval ForwardTo=if(match(valueExtracted, "^[^@]+@[^@]+\\.[^@]+$"), valueExtracted, null) 
12| dedup ForwardTo 
13| where isnotnull(ForwardTo) 
14| stats count min(_time) as firstTime max(_time) as lastTime values(Name) as Name by user Operation ForwardTo 
15| `security_content_ctime(firstTime)` 
16| `security_content_ctime(lastTime)` 
17| `o365_new_email_forwarding_rule_enabled_filter`

Data Source

Name Platform Sourcetype Source Supported App
N/A N/A N/A N/A N/A

Macros Used

Name Value
o365_management_activity sourcetype=o365:management:activity
o365_new_email_forwarding_rule_enabled_filter search *
o365_new_email_forwarding_rule_enabled_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
KillChainPhase.EXPLOITAITON
NistCategory.DE_CM
Cis18Value.CIS_10
Magic Hound
Silent Librarian
Kimsuky
LAPSUS$
Silent Librarian

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 Risk Score Impact Confidence
A forwarding email inbox rule was created for $user$ 42 70 60
The Risk Score is calculated by the following formula: Risk Score = (Impact * Confidence/100). Initial Confidence and Impact is set by the analytic author.

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: 2