Detection: O365 Email Suspicious Behavior Alert

Updated Date: 2024-04-01 ID: 85c7555a-05af-4322-81aa-76b4ddf52baa Author: Steven Dick Type: TTP Product: Splunk Enterprise Security

Description

The following analytic identifies when one of O365 the built-in security detections for suspicious email behaviors are triggered. These alerts often indicate that an attacker may have compromised a mailbox within the environment. Any detections from built-in Office 365 capabilities should be monitored and responded to appropriately. Certain premium Office 365 capabilities further enhance these detection and response functions.

1`o365_management_activity` Workload=SecurityComplianceCenter Operation=AlertEntityGenerated Name IN ("Suspicious email sending patterns detected","User restricted from sending email","Suspicious Email Forwarding Activity","Email sending limit exceeded") 
2| fromjson Data 
3| stats count min(_time) as firstTime max(_time) as lastTime by AlertId,ObjectId,Operation,Name 
4| rename Name as signature, AlertId as signature_id, ObjectId as user 
5| `security_content_ctime(firstTime)` 
6| `security_content_ctime(lastTime)` 
7| `o365_email_suspicious_behavior_alert_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_email_suspicious_behavior_alert_filter search *
o365_email_suspicious_behavior_alert_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 Email Collection Collection
T1114.003 Email Forwarding Rule Collection
KillChainPhase.EXPLOITAITON
NistCategory.DE_CM
Cis18Value.CIS_10
Magic Hound
Silent Librarian
Kimsuky
LAPSUS$
Silent Librarian

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. The alerts must be enabled in the o365 security portal.

Known False Positives

Users emailing for legitimate business purposes that appear suspicious.

Associated Analytic Story

Risk Based Analytics (RBA)

Risk Message Risk Score Impact Confidence
The user $user$ triggered the O365 security alert [$signature$] 90 90 100
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: 1