Azure AD External Guest User Invited
Description
The following analytic identifies the invitation of an external guest user within Azure AD. With Azure AD B2B collaboration, users and administrators can invite external users to collaborate with internal users. External guest account invitations should be monitored by security teams as they could potentially lead to unauthorized access. An example of this attack vector was described at BlackHat 2022 by security researcher Dirk-Jan during his tall Backdooring and Hijacking Azure AD Accounts by Abusing External Identities
- Type: TTP
-
Product: Splunk Enterprise, Splunk Enterprise Security, Splunk Cloud
- Last Updated: 2022-08-18
- Author: Gowthamaraj Rajendran, Mauricio Velazco, Splunk
- ID: c1fb4edb-cab1-4359-9b40-925ffd797fb5
Annotations
Kill Chain Phase
- Installation
NIST
- DE.CM
CIS20
- CIS 10
CVE
Search
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`azuread` "body.operationName"="Invite external user"
| rename body.properties.* as *
| rename targetResources{}.userPrincipalName as userPrincipalName
| rename initiatedBy.user.userPrincipalName as initiatedBy
| rename targetResources{}.type as type
| stats values(userPrincipalName) by _time, type, initiatedBy, result, body.operationName
| `azure_ad_external_guest_user_invited_filter`
Macros
The SPL above uses the following Macros:
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
- body.properties.targetResources{}.userPrincipalName
- body.properties.targetResources{}.type
- body.properties.initiatedBy.user.userPrincipalName
- body.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. Specifically, this analytic leverages the AuditLogs log category.
Known False Positives
Administrator may legitimately invite external guest users. Filter as needed.
Associated Analytic Story
RBA
Risk Score | Impact | Confidence | Message |
---|---|---|---|
45.0 | 50 | 90 | External Guest User $userPrincipalName$ 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: 1