Azure AD External Guest User Invited

SPLUNK detection rule by Gowthamaraj Rajendran, Mauricio Velazco, Splunk · Apache-2.0

The following analytic detects the invitation of an external guest user within Azure AD. It leverages Azure AD AuditLogs to identify events where an external user is invited, using fields such as operationName and initiatedBy. Monitoring these invitations is crucial as they can lead to unauthorized access if abused. If confirmed malicious, this activity could allow attackers to gain access to internal resources, potentially leading to data breaches or further exploitation of the environment.

name: Azure AD External Guest User Invited
id: c1fb4edb-cab1-4359-9b40-925ffd797fb5
version: 12
creation_date: '2022-08-19'
modification_date: '2026-05-13'
author: Gowthamaraj Rajendran, Mauricio Velazco, Splunk
status: production
type: TTP
description: The following analytic detects the invitation of an external guest user within Azure AD. It leverages Azure AD AuditLogs to identify events where an external user is invited, using fields such as operationName and initiatedBy. Monitoring these invitations is crucial as they can lead to unauthorized access if abused. If confirmed malicious, this activity could allow attackers to gain access to internal resources, potentially leading to data breaches or further exploitation of the environment.
data_source:
    - Azure Active Directory Invite external user
search: |-
    `azure_monitor_aad` operationName="Invite external user"
      | rename properties.* as *
      | rename initiatedBy.user.userPrincipalName as initiatedBy
      | rename targetResources{}.type as type
      | rename userAgent as user_agent
      | fillnull
      | stats count min(_time) as firstTime max(_time) as lastTime
        BY dest user src
           vendor_account vendor_product user_agent
           initiatedBy type signature
      | `security_content_ctime(firstTime)`
      | `security_content_ctime(lastTime)`
      | `azure_ad_external_guest_user_invited_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 AuditLogs log category.
known_false_positives: Administrator may legitimately invite external guest users. Filter as needed.
references:
    - https://dirkjanm.io/assets/raw/US-22-Mollema-Backdooring-and-hijacking-Azure-AD-accounts_final.pdf
    - https://www.blackhat.com/us-22/briefings/schedule/#backdooring-and-hijacking-azure-ad-accounts-by-abusing-external-identities-26999
    - https://attack.mitre.org/techniques/T1136/003/
    - https://docs.microsoft.com/en-us/azure/active-directory/external-identities/b2b-quickstart-add-guest-users-portal
drilldown_searches:
    - name: View the detection results for - "$user$"
      search: '%original_detection_search% | search  user = "$user$"'
      earliest_offset: $info_min_time$
      latest_offset: $info_max_time$
    - name: View risk events for the last 7 days for - "$user$"
      search: '| from datamodel Risk.All_Risk | search normalized_risk_object IN ("$user$") | stats count min(_time) as firstTime max(_time) as lastTime values(search_name) as "Search Name" values(risk_message) as "Risk Message" values(analyticstories) as "Analytic Stories" values(annotations._all) as "Annotations" values(annotations.mitre_attack.mitre_tactic) as "ATT&CK Tactics" by normalized_risk_object | `security_content_ctime(firstTime)` | `security_content_ctime(lastTime)`'
      earliest_offset: 7d
      latest_offset: "0"
finding:
    title: External Guest User $user$ initiated by $initiatedBy$
    entity:
        field: user
        type: user
        score: 50
intermediate_findings:
    entities:
        - field: initiatedBy
          type: user
          score: 50
          message: External Guest User $user$ initiated by $initiatedBy$
analytic_story:
    - Azure Active Directory Persistence
asset_type: Azure Active Directory
mitre_attack_id:
    - T1136.003
product:
    - Splunk Enterprise
    - Splunk Enterprise Security
    - Splunk Cloud
category: cloud
security_domain: threat
tests:
    - name: True Positive Test
      attack_data:
        - data: https://media.githubusercontent.com/media/splunk/attack_data/master/datasets/attack_techniques/T1136.003/azure_ad_external_guest_user_invited/azure-audit.log
          source: Azure AD
          sourcetype: azure:monitor:aad
      test_type: unit

[[ currentRule.title && currentRule.title.length > 60 ? currentRule.title.slice(0, 60) + '…' : currentRule.title ]]

13bada22-06ee-44e1-b241-9cc605d1d67e

Propose edits, view related rules, and engage with the community through comments.

Executable code, not a declarative rule

This submission is arbitrary [[ currentRule.format ? currentRule.format.toUpperCase() : '' ]] code, not a declarative detection rule — review it as you would any script before running it, and note that it cannot be safely aggregated or auto-executed alongside YARA/Sigma/Suricata/CRS rules.

Rejected pattern present

[[ reason ]]

What does this mean?

Format & documentation suggestions

Not a security issue — this rule is valid and was accepted as-is. These are optional fields/conventions its own format recommends, mainly affecting its quality score and how well it documents itself for other reviewers.

[[ reason ]]

What do these messages mean?

[[ currentRule.title && currentRule.title.length > 60 ? currentRule.title.slice(0, 60) + '…' : currentRule.title ]]

[[ currentRule.title ]]

Community Discussion