Azure AD User ImmutableId Attribute Updated

name: Azure AD User ImmutableId Attribute Updated
id: 0c0badad-4536-4a84-a561-5ff760f3c00e
version: 13
creation_date: '2022-09-02'
modification_date: '2026-05-13'
author: Mauricio Velazco, Gowthamaraj Rajendran, Splunk
status: production
type: TTP
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.
data_source:
    - Azure Active Directory Update user
search: |-
    `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
      | fillnull
      | stats count min(_time) as firstTime max(_time) as lastTime
        BY dest user src
           vendor_account vendor_product initiatedBy
           signature
      | `security_content_ctime(firstTime)`
      | `security_content_ctime(lastTime)`
      | `azure_ad_user_immutableid_attribute_updated_filter`
how_to_implement: 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 AuditLog log category.
known_false_positives: The SourceAnchor (also called ImmutableId) Azure AD attribute has legitimate uses for directory synchronization. Investigate and filter as needed.
references:
    - https://docs.microsoft.com/en-us/azure/active-directory/hybrid/plan-connect-design-concepts
    - https://www.mandiant.com/resources/remediation-and-hardening-strategies-microsoft-365-defend-against-apt29-v13
    - https://o365blog.com/post/federation-vulnerability/
    - https://www.inversecos.com/2021/11/how-to-detect-azure-active-directory.html
    - https://www.mandiant.com/resources/blog/detecting-microsoft-365-azure-active-directory-backdoors
    - https://attack.mitre.org/techniques/T1098/
finding:
    title: The SourceAnchor or ImmutableID attribute has been modified for user $user$ by $initiatedBy$
    entity:
        field: initiatedBy
        type: user
        score: 50
intermediate_findings:
    entities:
        - field: user
          type: user
          score: 50
          message: The SourceAnchor or ImmutableID attribute has been modified for user $user$ by $initiatedBy$
analytic_story:
    - Azure Active Directory Persistence
    - Hellcat Ransomware
asset_type: Azure Active Directory
mitre_attack_id:
    - T1098
product:
    - Splunk Enterprise
    - Splunk Enterprise Security
    - Splunk Cloud
category: cloud
security_domain: threat