Detection: O365 Cross-Tenant Access Change

Updated Date: 2024-04-11 ID: 7c0fa490-12b0-4d0b-b9f5-e101d1e0e06f Author: Steven Dick Type: TTP Product: Splunk Enterprise Security

Description

The following analytic identifies when cross-tenant access/synchronization policies are changed in an Azure tenant. Adversaries have been observed altering victim cross-tenant policies as a method of lateral movement or maintaining persistent access to compromised environments. These policies should be considered sensitive and monitored for changes and/or loose configuration.

Search

1`o365_management_activity` Workload=AzureActiveDirectory Operation IN ("Add a partner to cross-tenant access setting.","Delete partner specific cross-tenant access setting.") 
2| eval 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| stats values(Workload) as category, values(ClientIP) as src, values(ModifiedProperties{}.Name) as object_name, values(ModifiedProperties{}.NewValue) as object_attrs, count, min(_time) as firstTime, max(_time) as lastTime by Id,user,Operation 
4| rename Operation as signature, Id as signature_id 
5| `security_content_ctime(firstTime)`  
6| `security_content_ctime(lastTime)` 
7| `o365_cross_tenant_access_change_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_cross_tenant_access_change_filter	`search *`

o365_cross_tenant_access_change_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
T1484.002	Trust Modification	Defense Evasion

KillChainPhase.EXPLOITAITON

NistCategory.DE_CM

Cis18Value.CIS_10

Scattered Spider

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
The user [$user$] changed the Azure cross-tenant access settings for $object_name$ $object_attrs$ [$signature$]	56	75	75

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