Azure AD External Guest User Invited

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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.

• Type: TTP

• Product: Splunk Enterprise, Splunk Enterprise Security, Splunk Cloud

• Last Updated: 2024-05-11
• Author: Gowthamaraj Rajendran, Mauricio Velazco, Splunk
• ID: c1fb4edb-cab1-4359-9b40-925ffd797fb5

Annotations

ATT&CK

ATT&CK

ID	Technique	Tactic
T1136.003	Cloud Account	Persistence

Kill Chain Phase

• Installation

NIST

• DE.CM

CIS20

• CIS 10

CVE

Search

`azure_monitor_aad` operationName="Invite external user" 
| rename properties.*  as * 
| rename initiatedBy.user.userPrincipalName as initiatedBy 
| rename targetResources{}.type as type 
| stats count min(_time) as firstTime max(_time) as lastTime values(user) as user by type, initiatedBy, result, operationName 
| `security_content_ctime(firstTime)` 
| `security_content_ctime(lastTime)` 
| `azure_ad_external_guest_user_invited_filter`

Macros

The SPL above uses the following Macros:

• azure_monitor_aad
• security_content_ctime

azure_ad_external_guest_user_invited_filter is a empty macro by default. It allows the user to filter out any results (false positives) without editing the SPL.

Required fields

List of fields required to use this analytic.

• _time
• user
• properties.targetResources{}.type
• properties.initiatedBy.user.userPrincipalName
• properties.result

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.

Associated Analytic Story

• Azure Active Directory Persistence

RBA

Risk Score	Impact	Confidence	Message
45.0	50	90	External Guest User $user$ initiated by $initiatedBy$

The Risk Score is calculated by the following formula: Risk Score = (Impact * Confidence/100). Initial Confidence and Impact is set by the analytic author.

Reference

• 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

Test Dataset

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 | version: 3