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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.

  • Type: TTP
  • Product: Splunk Enterprise, Splunk Enterprise Security, Splunk Cloud
  • Datamodel: Change
  • Last Updated: 2024-05-15
  • Author: Patrick Bareiss, Mauricio Velazco, Splunk
  • ID: 2246c142-a678-45f8-8546-aaed7e0efd30

Annotations

ATT&CK

ATT&CK

ID Technique Tactic
T1098 Account Manipulation Persistence, Privilege Escalation
T1098.002 Additional Email Delegate Permissions Persistence, Privilege Escalation
Kill Chain Phase
  • Installation
  • Exploitation
NIST
  • DE.CM
CIS20
  • CIS 10
CVE 


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 `o365_management_activity` Workload=Exchange Operation=Add-MailboxPermission 
| search (AccessRights=FullAccess OR AccessRights=ChangePermission OR AccessRights=ChangeOwner) 
| rename Identity AS dest_user 
| stats count earliest(_time) as firstTime latest(_time) as lastTime by user dest_user Operation AccessRights 
|`security_content_ctime(firstTime)` 
|`security_content_ctime(lastTime)` 
| `o365_elevated_mailbox_permission_assigned_filter`

Macros

The SPL above uses the following Macros:

:information_source: o365_elevated_mailbox_permission_assigned_filter is a empty macro by default. It allows the user to filter out any results (false positives) without editing the SPL.

Required fields

List of fields required to use this analytic.

  • _time
  • Workload
  • Operation
  • AccessRights
  • user
  • src_user
  • dest_user

How To Implement

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

RBA

Risk Score Impact Confidence Message
42.0 60 70 Elevated mailbox permissions were assigned on $dest_user$

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

Reference

Test Dataset

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 | version: 2