O365 Exfiltration via File Sync Download
The following analytic detects when an excessive number of files are sync from o365 by the same user over a short period of time. A malicious actor abuse the user-agent string through GUI or API access to evade…
Description
The following analytic detects when an excessive number of files are sync from o365 by the same user over a short period of time. A malicious actor abuse the user-agent string through GUI or API 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 taken 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 sync scenarios may trigger this alert, specifically OneNote. 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
- 350837b5-13d3-4c06-b688-db07afbe5050
- 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