O365 New MFA Method Registered

name: O365 New MFA Method Registered
id: 4e12db1f-f7c7-486d-8152-a221cad6ac2b
version: 11
creation_date: '2023-12-06'
modification_date: '2026-05-13'
author: Mauricio Velazco, Splunk
status: production
type: TTP
description: The following analytic detects the registration of a new Multi-Factor Authentication (MFA) method for a user account within Office 365. It leverages O365 audit logs to identify changes in MFA configurations. This activity is significant as it may 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 or access sensitive data. Immediate verification and remediation are required to secure the affected account.
data_source:
    - O365 Update user.
search: |
    `o365_management_activity`
    Workload=AzureActiveDirectory
    Operation="Update user."
    | eval propertyName = mvindex('ModifiedProperties{}.Name', 0)
    | search propertyName IN ("StrongAuthenticationMethod", "StrongAuthenticationPhoneAppDetail")
    | eval oldvalue = mvindex('ModifiedProperties{}.OldValue',0)
    | eval newvalue = mvindex('ModifiedProperties{}.NewValue',0)
    | rex field=newvalue max_match=0 "(?i)(?<new_method_type>MethodType|DeviceName)"
    | rex field=oldvalue max_match=0 "(?i)(?<old_method_type>MethodType|DeviceName)"
    | eval count_new_method_type = coalesce(mvcount(new_method_type), 0)
    | eval count_old_method_type = coalesce(mvcount(old_method_type), 0)
    | where count_new_method_type > count_old_method_type
    | fillnull
    | stats earliest(_time) as firstTime
            latest(_time) as lastTime
            values(propertyName) as propertyName
      by user newvalue oldvalue vendor_account
         vendor_product dest signature src
    | `security_content_ctime(firstTime)`
    | `security_content_ctime(lastTime)`
    | `o365_new_mfa_method_registered_filter`
how_to_implement: You must install the Splunk Microsoft Office 365 Add-on and ingest Office 365 management activity events.
known_false_positives: Users may register MFA methods legitimately, investigate and filter as needed.
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
finding:
    title: A new MFA method was added for $user$
    entity:
        field: user
        type: user
        score: 50
analytic_story:
    - Office 365 Persistence Mechanisms
asset_type: O365 Tenant
mitre_attack_id:
    - T1098.005
product:
    - Splunk Enterprise
    - Splunk Enterprise Security
    - Splunk Cloud
category: cloud
security_domain: identity