Detection: O365 OAuth App Mailbox Access via Graph API

Updated Date: 2024-05-18 ID: 9db0d5b0-4058-4cb7-baaf-77d8143539a2 Author: Mauricio Velazco, Splunk Type: TTP Product: Splunk Enterprise Security

Description

The following analytic detects when emails are accessed in Office 365 Exchange via the Microsoft Graph API using the client ID '00000003-0000-0000-c000-000000000000'. It leverages the 'MailItemsAccessed' operation within the Exchange workload, focusing on OAuth-authenticated applications. This activity is significant as unauthorized access to emails can lead to data breaches and information theft. If confirmed malicious, attackers could exfiltrate sensitive information, compromise user accounts, and further infiltrate the organization’s network.

Search

1 `o365_management_activity` Workload=Exchange Operation=MailItemsAccessed AppId=* AppId=00000003-0000-0000-c000-000000000000 
2|  stats count earliest(_time) as firstTime latest(_time) as lastTime values(ClientIPAddress) by user ClientAppId OperationCount AppId 
3| `security_content_ctime(firstTime)` 
4| `security_content_ctime(lastTime)` 
5| `o365_oauth_app_mailbox_access_via_graph_api_filter`

Data Source

Name	Platform	Sourcetype	Source	Supported App
O365 MailItemsAccessed	N/A	`'o365:management:activity'`	`'o365'`	N/A

Macros Used

Name	Value
o365_management_activity	`sourcetype=o365:management:activity`
o365_oauth_app_mailbox_access_via_graph_api_filter	`search *`

o365_oauth_app_mailbox_access_via_graph_api_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
T1114.002	Remote Email Collection	Collection

KillChainPhase.EXPLOITAITON

NistCategory.DE_CM

Cis18Value.CIS_10

APT1

APT28

APT29

Chimera

Dragonfly

FIN4

HAFNIUM

Ke3chang

Kimsuky

Leafminer

Magic Hound

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

OAuth applications may access mailboxes for legitimate purposes, you can use the ClientAppId to add trusted applications to an allow list.

Associated Analytic Story

Risk Based Analytics (RBA)

Risk Message	Risk Score	Impact	Confidence
An OAuth application identified with id $ClientAppId$ accesed mailboxes through the Graph API.	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