Detection: O365 Cross-Tenant Access Change

Updated Date: 2024-09-30 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.

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

No data sources specified for this detection.

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

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: 3