Multi-Mailbox Access by Single IP via Cloud App Permissions
Identifies a single IP address accessing an abnormally large number of distinct mailboxes via MailItemsAccessed events, indicating a service principal or OAuth app silently reading mail across the organization using…
Description
Identifies a single IP address accessing an abnormally large number of distinct mailboxes via MailItemsAccessed events, indicating a service principal or OAuth app silently reading mail across the organization using granted permissions. Empty UserAgent combined with high mailbox count indicates programmatic API access consistent with app-based exfiltration.
Detection logic
Detection requirements
- Platform
- ESXiIaaSLinuxmacOSNetwork DevicesOffice SuiteSaaSWindows
The rule states no platform. This is derived from the 3 ATT&CK techniques it maps to.
- Log source product
- microsoftcloudappsecuritymicrosoftdefenderthreatintelligence
- Log source service
- cloudappeventsthreatintelindicators
MITRE ATT&CK mappings
0 exclusive techniques.This is coverage no other published rule has; it is not this rule's total technique count.
No references are available for this detection.
From the source
- At source
- Open at source
- Upstream identifier
- c53bf4ae-bd8b-4c72-b9c3-10baa8c13885
- Tagged by the source as
- CollectionExfiltration
Licence
- Published under
- MIT LicenseRead the licence
- Attribution
- Required
- Obtained under
- MITRead the origin licence
Authorship
- Published
- Sep 1, 2026
- Version
- 1