LoFP / the sourceanchor (also called immutableid) azure ad attribute has legitimate uses for directory synchronization. investigate and filter as needed.

Techniques

• T1098

Sample rules

Azure AD User ImmutableId Attribute Updated

• source: splunk
• technicques:
  • T1098

Description

The following analytic identifies the modification of the SourceAnchor (ImmutableId) attribute for an Azure Active Directory user. This detection leverages Azure AD audit logs, specifically monitoring the “Update user” operation and changes to the SourceAnchor attribute. This activity is significant as it is a step in setting up an Azure AD identity federation backdoor, allowing an adversary to establish persistence. If confirmed malicious, the attacker could impersonate any user, bypassing password and MFA requirements, leading to unauthorized access and potential data breaches.

Detection logic

`azure_monitor_aad`  operationName="Update user" properties.targetResources{}.modifiedProperties{}.displayName=SourceAnchor 
| rename properties.* as * 
| rename initiatedBy.user.userPrincipalName as initiatedBy 
| rename targetResources{}.modifiedProperties{}.newValue as modifiedProperties 
| stats count min(_time) as firstTime max(_time) as lastTime values(user) as user values(modifiedProperties) as modifiedProperties by initiatedBy, src_ip, result, operationName 
| `security_content_ctime(firstTime)` 
| `security_content_ctime(lastTime)` 
| `azure_ad_user_immutableid_attribute_updated_filter`