Detection: O365 Mailbox Email Forwarding Enabled

Updated Date: 2024-05-24 ID: 0b6bc75c-05d1-4101-9fc3-97e706168f24 Author: Patrick Bareiss, Mauricio Velazco, Splunk Type: TTP Product: Splunk Enterprise Security

Description

The following analytic identifies instances where email forwarding has been enabled on mailboxes within an Office 365 environment. It detects this activity by monitoring the Set-Mailbox operation within the o365_management_activity logs, specifically looking for changes to the ForwardingAddress or ForwardingSmtpAddress parameters. This activity is significant as unauthorized email forwarding can lead to data exfiltration and unauthorized access to sensitive information. If confirmed malicious, attackers could intercept and redirect emails, potentially compromising confidential communications and leading to data breaches.

Search

 1`o365_management_activity` Operation=Set-Mailbox  
 2| eval match1=mvfind('Parameters{}.Name', "ForwardingAddress") 
 3| eval match2=mvfind('Parameters{}.Name', "ForwardingSmtpAddress") 
 4| where match1>= 0 OR match2>= 0 
 5| eval ForwardTo=coalesce(ForwardingAddress, ForwardingSmtpAddress) 
 6| search ForwardTo!=""  
 7| rename user_id as user 
 8| stats count earliest(_time) as firstTime latest(_time) as lastTime values(ForwardTo) as ForwardTo by user ObjectId 
 9|`security_content_ctime(firstTime)`  
10|`security_content_ctime(lastTime)` 
11| `o365_mailbox_email_forwarding_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_mailbox_email_forwarding_enabled_filter	`search *`

o365_mailbox_email_forwarding_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

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

Associated Analytic Story

Office 365 Collection Techniques

Risk Based Analytics (RBA)

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