Detection: Azure AD New MFA Method Registered

Description

The following analytic detects the registration of a new Multi-Factor Authentication (MFA) method for a user account in Azure Active Directory. It leverages Azure AD audit logs to identify changes in MFA configurations. This activity is significant because adding a new MFA method can indicate an attacker's attempt to maintain persistence on a compromised account. If confirmed malicious, the attacker could bypass existing security measures, solidify their access, and potentially escalate privileges, access sensitive data, or make unauthorized changes. Immediate verification and remediation are required to secure the affected account.

Search

 1`azure_monitor_aad` operationName="Update user" 
 2| rename properties.* as * 
 3| eval propertyName = mvindex('targetResources{}.modifiedProperties{}.displayName',0) 
 4| search propertyName = StrongAuthenticationMethod 
 5| eval oldvalue = mvindex('targetResources{}.modifiedProperties{}.oldValue',0) 
 6| eval newvalue = mvindex('targetResources{}.modifiedProperties{}.newValue',0) 
 7| rex field=newvalue max_match=0 "(?i)(?<new_method_type>\"MethodType\")" 
 8| rex field=oldvalue max_match=0 "(?i)(?<old_method_type>\"MethodType\")" 
 9| eval count_new_method_type = coalesce(mvcount(new_method_type), 0) 
10| eval count_old_method_type = coalesce(mvcount(old_method_type), 0) 
11| fillnull 
12| stats count min(_time) as firstTime max(_time) as lastTime by dest user src vendor_account vendor_product newvalue oldvalue signature 
13| `security_content_ctime(firstTime)` 
14| `security_content_ctime(lastTime)` 
15| `azure_ad_new_mfa_method_registered_filter`

Data Source

Name	Platform	Sourcetype	Source
Azure Active Directory Update user	Azure	'azure:monitor:aad'	'Azure AD'

Macros Used

Annotations

Default Configuration

This detection is configured by default in Splunk Enterprise Security to run with the following settings:

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 through an EventHub. This analytic was written to be used with the azure:monitor:aad sourcetype leveraging the AuditLog log category.

Known False Positives

Users may register MFA methods legitimally, investigate and filter as needed.

Associated Analytic Story

• Azure Active Directory Persistence

• Scattered Lapsus$ Hunters

Finding

References

• https://attack.mitre.org/techniques/T1098/005/

• https://www.microsoft.com/en-us/security/blog/2023/06/08/detecting-and-mitigating-a-multi-stage-aitm-phishing-and-bec-campaign/

• https://www.csoonline.com/article/573451/sophisticated-bec-scammers-bypass-microsoft-365-multi-factor-authentication.html

Detection Testing

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: 12