Suspicious Copy of Outlook OST Email Data File for Exfiltration
- Product
- windows
- Category
- process_creation
- Author
- HuntRule
- Published
- 2026-05-26
- Updated
- 2026-08-28
ATT&CK techniques
CollectionRecon
Resource Dev
Initial Access
Execution
Persistence
Priv Esc
Defense Evasion
Cred Access
Discovery
Lateral Movement
Collection
C2
Exfiltration
Impact
What it detects
This rule detects copying of an Outlook OST offline data file, a collection step used by the ToddyCat APT before extracting messages with XstExport. The attackers used xcopy to duplicate the .ost mailbox cache to a .ost2 file so its contents could be parsed offline. Copying a locked mailbox data file is a strong indicator of local email collection ahead of exfiltration.
Reporting behind it
Detection content is published as a reviewed draft. Tune thresholds and exclusions against your own telemetry before enabling this rule for alerting.
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Also included
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