Suspicious DLL Sideloading via usysdiag.exe Loading sensapi.dll via NailaoLocker (via image_load)

ATT&CK techniques

Execution → Defense Evasion

Recon
Resource Dev
Initial Access
Execution
- T1574.001DLL
Persistence
- T1574.001DLL
Priv Esc
- T1574.001DLL
Defense Evasion
- T1574.001DLL
Cred Access
Discovery
Lateral Movement
Collection
C2
Exfiltration
Impact

What it detects

This rule detects the NailaoLoader stage of NailaoLocker ransomware which side loads a malicious sensapi.dll through the legitimate security tool usysdiag.exe to decrypt and run the locker payload. The genuine sensapi.dll ships in System32 so a copy loaded from the usysdiag application directory is anomalous. This pairing indicates the loader.

Reporting behind it

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Suspicious DLL Sideloading via usysdiag.exe Loading sensapi.dll via NailaoLocker (via image_load)

Pivot detection · T1574.001 · 9 related

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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