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Description

The following analytic identifies instances where read permissions are granted to mailbox folders within an Office 365 environment. It detects this activity by monitoring the o365_management_activity data source for the Set-MailboxFolderPermission and Add-MailboxFolderPermission operations. This behavior is significant as it may indicate unauthorized access or changes to mailbox folder permissions, potentially exposing sensitive email content. If confirmed malicious, an attacker could gain unauthorized access to read email communications, leading to data breaches or information leakage.

  • Type: TTP

  • Product: Splunk Enterprise, Splunk Enterprise Security, Splunk Cloud

  • Last Updated: 2024-05-25
  • Author: Mauricio Velazco, Splunk
  • ID: cd15c0a8-470e-4b12-9517-046e4927db30

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="Set-MailboxFolderPermission" OR Operation="Add-MailboxFolderPermission" ) 
| eval isReadRole=if(match(AccessRights, "^(ReadItems
|Author
|NonEditingAuthor
|Owner
|PublishingAuthor
|Reviewer)$"), "true", "false") 
| search isReadRole="true" 
| rename UserId as user 
| stats count earliest(_time) as firstTime latest(_time) as lastTime by Operation, user, Identity, AccessRights 
| `security_content_ctime(firstTime)` 
| `security_content_ctime(lastTime)` 
| `o365_mailbox_folder_read_permission_granted_filter`

Macros

The SPL above uses the following Macros:

:information_source: o365_mailbox_folder_read_permission_granted_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
  • Operation
  • AccessRights
  • UserId
  • Identity
  • User

How To Implement

You must install the Splunk Microsoft Office 365 Add-on and ingest Office 365 management activity events.

Known False Positives

Mailbox folder permissions may be configured for legitimate purposes, filter as needed.

Associated Analytic Story

RBA

Risk Score Impact Confidence Message
42.0 70 60 A folder was granted read permission by $user$

: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