Detection: O365 Elevated Mailbox Permission Assigned

Updated Date: 2024-09-24 ID: 2246c142-a678-45f8-8546-aaed7e0efd30 Author: Patrick Bareiss, Mauricio Velazco, Splunk Type: TTP Product: Splunk Enterprise Security

Description

The following analytic identifies the assignment of elevated mailbox permissions in an Office 365 environment via the Add-MailboxPermission operation. It leverages logs from the Exchange workload in the o365_management_activity data source, focusing on permissions such as FullAccess, ChangePermission, or ChangeOwner. This activity is significant as it indicates potential unauthorized access or control over mailboxes, which could lead to data exfiltration or privilege escalation. If confirmed malicious, attackers could gain extensive access to sensitive email data and potentially manipulate mailbox settings, posing a severe security risk.

Search

1`o365_management_activity` Workload=Exchange Operation=Add-MailboxPermission 
2| search (AccessRights=FullAccess OR AccessRights=ChangePermission OR AccessRights=ChangeOwner) 
3| rename Identity AS dest_user 
4| stats count earliest(_time) as firstTime latest(_time) as lastTime by user dest_user Operation AccessRights 
5|`security_content_ctime(firstTime)` 
6|`security_content_ctime(lastTime)` 
7| `o365_elevated_mailbox_permission_assigned_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_elevated_mailbox_permission_assigned_filter	`search *`

o365_elevated_mailbox_permission_assigned_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
T1098	Account Manipulation	Persistence
T1098.002	Additional Email Delegate Permissions	Privilege Escalation

KillChainPhase.EXPLOITAITON

KillChainPhase.INSTALLATION

NistCategory.DE_CM

Cis18Value.CIS_10

APT3

APT41

APT5

Dragonfly

FIN13

HAFNIUM

Kimsuky

Lazarus Group

Magic Hound

APT28

APT29

Magic Hound

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

FullAccess mailbox delegation may be assigned for legitimate purposes, filter as needed.

Associated Analytic Story

Office 365 Collection Techniques

Risk Based Analytics (RBA)

Risk Message	Risk Score	Impact	Confidence
Elevated mailbox permissions were assigned on $dest_user$	42	60	70

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:management:activity`	`o365:management:activity`
Integration	✅ Passing	Dataset	`o365:management:activity`	`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