ID | Technique | Tactic |
---|---|---|
T1114.002 | Remote Email Collection | Collection |
Detection: O365 OAuth App Mailbox Access via EWS
Description
The following analytic detects when emails are accessed in Office 365 Exchange via Exchange Web Services (EWS) using OAuth-authenticated applications. It leverages the ClientInfoString field to identify EWS interactions and aggregates metrics such as access counts, timing, and client IP addresses, categorized by user, ClientAppId, OperationCount, and AppId. Monitoring OAuth applications accessing emails through EWS is crucial for identifying potential abuse or unauthorized data access. If confirmed malicious, this activity could lead to unauthorized email access, data exfiltration, or further compromise of sensitive information.
Search
1`o365_management_activity` Workload=Exchange Operation=MailItemsAccessed AppId=* ClientAppId=*
2| regex ClientInfoString="^Client=WebServices;ExchangeWebServices"
3| stats count earliest(_time) as firstTime latest(_time) as lastTime values(ClientIPAddress) as src_ip by user ClientAppId OperationCount AppId ClientInfoString
4| `security_content_ctime(firstTime)`
5| `security_content_ctime(lastTime)`
6| `o365_oauth_app_mailbox_access_via_ews_filter`
Data Source
Name | Platform | Sourcetype | Source | Supported App |
---|---|---|---|---|
O365 MailItemsAccessed | N/A | 'o365:management:activity' |
'o365' |
N/A |
Macros Used
Name | Value |
---|---|
o365_management_activity | sourcetype=o365:management:activity |
o365_oauth_app_mailbox_access_via_ews_filter | search * |
o365_oauth_app_mailbox_access_via_ews_filter
is an empty macro by default. It allows the user to filter out any results (false positives) without editing the SPL.
Annotations
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 |
Implementation
You must install the Splunk Microsoft Office 365 Add-on and ingest Office 365 management activity events.
Known False Positives
OAuth applications may access mailboxes for legitimate purposes, you can use the src_ip to add trusted sources to an allow list.
Associated Analytic Story
Risk Based Analytics (RBA)
Risk Message | Risk Score | Impact | Confidence |
---|---|---|---|
An OAuth application identified with id $ClientAppId$ accesed mailboxes through the Graph API. | 42 | 70 | 60 |
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