Detection: Azure AD New Custom Domain Added

Updated Date: 2024-09-24 ID: 30c47f45-dd6a-4720-9963-0bca6c8686ef Author: Mauricio Velazco, Gowthamaraj Rajendran, Splunk Type: TTP Product: Splunk Enterprise Security

Description

The following analytic detects the addition of a new custom domain within an Azure Active Directory (AD) tenant. It leverages Azure AD AuditLogs to identify successful "Add unverified domain" operations. This activity is significant as it may indicate an adversary attempting to establish persistence by setting up identity federation backdoors, allowing them to impersonate users and bypass authentication mechanisms. If confirmed malicious, this could enable attackers to gain unauthorized access, escalate privileges, and maintain long-term access to the Azure AD environment, posing a severe security risk.

Search

1`azure_monitor_aad`  operationName="Add unverified domain" properties.result=success 
2| rename properties.* as * 
3| rename targetResources{}.displayName as domain 
4| stats count min(_time) as firstTime max(_time) as lastTime by user, domain, result, operationName, src_ip 
5| `security_content_ctime(firstTime)` 
6| `security_content_ctime(lastTime)` 
7| `azure_ad_new_custom_domain_added_filter`

Data Source

Name	Platform	Sourcetype	Source	Supported App
Azure Active Directory Add unverified domain	Azure	`'azure:monitor:aad'`	`'Azure AD'`	N/A

Macros Used

Name	Value
azure_monitor_aad	`sourcetype=azure:monitor:aad`
azure_ad_new_custom_domain_added_filter	`search *`

azure_ad_new_custom_domain_added_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
T1484	Domain or Tenant Policy Modification	Defense Evasion
T1484.002	Trust Modification	Privilege Escalation

KillChainPhase.EXPLOITAITON

NistCategory.DE_CM

Cis18Value.CIS_10

Scattered Spider

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 latest version of Splunk Add-on for Microsoft Cloud Services from Splunkbase (https://splunkbase.splunk.com/app/3110/#/details). You must be ingesting Azure Active Directory events into your Splunk environment. This analytic was written to be used with the azure:monitor:aad sourcetype leveraging the AuditLogs log category.

Known False Positives

In most organizations, new customm domains will be updated infrequently. Filter as needed.

Associated Analytic Story

Azure Active Directory Persistence

Risk Based Analytics (RBA)

Risk Message	Risk Score	Impact	Confidence
A new custom domain, $domain$ , was added by $user$	54	60	90

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	`Azure AD`	`azure:monitor:aad`
Integration	✅ Passing	Dataset	`Azure AD`	`azure:monitor:aad`

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: 4