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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.

Known benign triggers

  • It is possible that certain file sync scenarios may trigger this alert, specifically OneNote. Adjust threshold and filtering as needed.

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