O365 Exfiltration via File Access
The following analytic detects when an excessive number of files are access from o365 by the same user over a short period of time. A malicious actor may abuse the "open in app" functionality of SharePoint through…
Description
The following analytic detects when an excessive number of files are access from o365 by the same user over a short period of time. A malicious actor may abuse the "open in app" functionality of SharePoint through scripted or Graph API based access to evade triggering the FileDownloaded Event. This behavior may indicate an attacker staging data for exfiltration or an insider threat removing organizational data. Additional attention should be take with any Azure Guest (#EXT#) accounts.
Detection logic
Detection requirements
- Platform
- ESXiIaaSLinuxmacOSOffice SuiteSaaSWindows
The rule states no platform. This is derived from the 2 ATT&CK techniques it maps to.
- Log source category
- office_365_universal_audit_log
Known benign triggers
- It is possible that certain file access scenarios may trigger this alert, specifically OneDrive syncing and users accessing personal onedrives of other users. Adjust threshold and filtering as needed.
MITRE ATT&CK mappings
0 exclusive techniques.This is coverage no other published rule has; it is not this rule's total technique count.
References
| Reference | Cited by |
|---|---|
| attack.mitre.org/techniques/T1567/exfil | 3 |
| thedfirjournal.com/posts/m365-data-exfiltration-rclone/ | 3 |
| www.varonis.com/blog/sidestepping-detection-while-exfiltrating-sharepoint-data | 3 |
From the source
- At source
- Open at source
- Upstream identifier
- 80b44ae2-60ff-43f1-8e56-34beb49a340a
- Tagged by the source as
- Data ExfiltrationOffice 365 Account TakeoverO365 TenantcloudSplunk CloudSplunk EnterpriseSplunk Enterprise Securitythreat
Licence
- Published under
- Apache License 2.0Read the licence
- Attribution
- Required
- Obtained under
- Apache-2.0Read the origin licence
Authorship
- Written by
- Published
- Aug 26, 2026
- Version
- 1