| ID | Technique | Tactic |
|---|---|---|
| T1136.003 | Cloud Account | Persistence |
Detection: O365 External Identity Policy Changed
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
No data sources specified for this detection.
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
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
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: 3