Detection: O365 Mailbox Read Access Granted to Application

Updated Date: 2024-09-30 ID: 27ab61c5-f08a-438a-b4d3-325e666490b3 Author: Mauricio Velazco, Splunk Type: TTP Product: Splunk Enterprise Security

Description

The following analytic identifies instances where the Mail.Read Graph API permissions are granted to an application registration within an Office 365 tenant. It leverages O365 audit logs, specifically events related to changes in application permissions within the AzureActiveDirectory workload. This activity is significant because the Mail.Read permission allows applications to access and read all emails within a user's mailbox, which often contain sensitive or confidential information. If confirmed malicious, this could lead to data exfiltration, spear-phishing attacks, or further compromise based on the information gathered from the emails.

 1`o365_management_activity` Operation="Update application." 
 2| eval json_data=mvindex('ModifiedProperties{}.NewValue', 0) 
 3| eval json_data=replace(json_data, "^\[\s*", "") 
 4| eval json_data=replace(json_data, "\s*\]$", "") 
 5| spath input=json_data path=RequiredAppPermissions{}.EntitlementId output=EntitlementIds 
 6| eval match_found=mvfind(EntitlementIds, "810c84a8-4a9e-49e6-bf7d-12d183f40d01") 
 7| where isnotnull(match_found) 
 8| stats max(_time) as lastTime values(EntitlementIds) as EntitlementIds by Operation, user, object 
 9| `security_content_ctime(lastTime)` 
10| `o365_mailbox_read_access_granted_to_application_filter`

Data Source

Name Platform Sourcetype Source
O365 Update application. N/A 'o365:management:activity' 'o365'

Macros Used

Name Value
o365_management_activity sourcetype=o365:management:activity
o365_mailbox_read_access_granted_to_application_filter search *
o365_mailbox_read_access_granted_to_application_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
T1114.002 Remote Email Collection Collection
T1114 Email Collection Collection
T1098 Account Manipulation Persistence
T1098.003 Additional Cloud Roles Privilege Escalation
KillChainPhase.EXPLOITAITON
KillChainPhase.INSTALLATION
NistCategory.DE_CM
Cis18Value.CIS_10
APT1
APT28
APT29
Chimera
Dragonfly
FIN4
HAFNIUM
Ke3chang
Kimsuky
Leafminer
Magic Hound
Star Blizzard
Ember Bear
Magic Hound
Scattered Spider
Silent Librarian
HAFNIUM
Lazarus Group
LAPSUS$
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

There are legitimate scenarios in wich an Application registrations requires Mailbox read access. Filter as needed.

Associated Analytic Story

Risk Based Analytics (RBA)

Risk Message Risk Score Impact Confidence
Application registration $object$ was grandes mailbox read access by $user$ 45 90 50
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