Detection: O365 External Identity Policy Changed

Updated Date: 2024-04-11 ID: 29af1725-7a72-4d2d-8a18-e697e79a62d3 Author: Steven Dick Type: TTP Product: Splunk Enterprise Security

Description

The following analytic identifies when changes are made to the external guest policies within Azure AD. With Azure AD B2B collaboration, users and administrators can invite external users to collaborate with internal users. This detection also attempts to highlight what may have changed. 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.

Search

 1`o365_management_activity` Workload=AzureActiveDirectory Operation="Update policy." Target{}.ID="B2BManagementPolicy" 
 2| eval object_attrs = mvindex('ModifiedProperties{}.NewValue',0), object_attrs_old = mvindex('ModifiedProperties{}.OldValue',0), object_name = mvindex('Target{}.ID',3), signature=Operation, user = case(match(mvindex('Actor{}.ID',-1),"User"),mvindex('Actor{}.ID',0),match(mvindex('Actor{}.ID',-1),"ServicePrincipal"),mvindex('Actor{}.ID',3),true(),mvindex('Actor{}.ID',0)) 
 3| spath input=object_attrs_old output=B2BOld path={} 
 4| spath input=B2BOld 
 5| rename B2BManagementPolicy.* as B2BManagementPolicyOld.* 
 6| spath input=object_attrs output=B2BNew path={} 
 7| spath input=B2BNew 
 8| eval object_attrs = 'B2BManagementPolicy.InvitationsAllowedAndBlockedDomainsPolicy.AllowedDomains{}' , object_attrs_old = 'B2BManagementPolicyOld.InvitationsAllowedAndBlockedDomainsPolicy.AllowedDomains{}' 
 9| eval diff_add=mvmap(object_attrs,if(isnull(mvfind(object_attrs_old,object_attrs)),object_attrs,null)) 
10| eval diff_remove=mvmap(object_attrs_old,if(isnull(mvfind(object_attrs,object_attrs_old)),object_attrs_old,null)) 
11| eval result = case(isnotnull(diff_add),"Added ".mvjoin(diff_add,","),isnotnull(diff_remove),"Removed ".mvjoin(diff_remove,",")), action = case(isnotnull(diff_add),"created",isnotnull(diff_remove),"deleted") 
12| stats values(object_attrs) as object_attrs, values(action) as action, values(result) as result, values(B2BManagementPolicy*) as B2BManagementPolicy*, count, min(_time) as firstTime, max(_time) as lastTime by user,signature,object_name 
13| `security_content_ctime(firstTime)`  
14| `security_content_ctime(lastTime)` 
15| `o365_external_identity_policy_changed_filter`

Data Source

Name	Platform	Sourcetype	Source	Supported App
N/A	N/A	N/A	N/A	N/A

Macros Used

Name	Value
o365_management_activity	`sourcetype=o365:management:activity`
o365_external_identity_policy_changed_filter	`search *`

o365_external_identity_policy_changed_filter is an empty macro by default. It allows the user to filter out any results (false positives) without editing the SPL.

Annotations

- MITRE ATT&CK

+ Kill Chain Phases

+ NIST

+ CIS

- Threat Actors

ID	Technique	Tactic
T1136.003	Cloud Account	Persistence

KillChainPhase.INSTALLATION

NistCategory.DE_CM

Cis18Value.CIS_10

APT29

LAPSUS$

Default Configuration

This detection is configured by default in Splunk Enterprise Security to run with the following settings:

Setting	Value
Disabled	true
Cron Schedule	`0 * * * *`
Earliest Time	`-70m@m`
Latest Time	`-10m@m`
Schedule Window	`auto`
Creates Notable	Yes
Rule Title	`%name%`
Rule Description	`%description%`
Notable Event Fields	user, dest
Creates Risk Event	True

This configuration file applies to all detections of type TTP. These detections will use Risk Based Alerting and generate Notable Events.

Implementation

You must install the Splunk Microsoft Office 365 Add-on and ingest Office 365 management activity events.

Known False Positives

Business approved changes by known administrators.

Associated Analytic Story

Azure Active Directory Persistence

Risk Based Analytics (RBA)

Risk Message	Risk Score	Impact	Confidence
User $user$ changed the external identity [$object_name$] policy - $result$	75	75	100

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

References

Detection Testing

Test Type	Status	Dataset	Source	Sourcetype
Validation	✅ Passing	N/A	N/A	N/A
Unit	✅ Passing	Dataset	`o365`	`o365:management:activity`
Integration	✅ Passing	Dataset	`o365`	`o365:management:activity`

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: GitHub | Version: 1