Suspicious Replacement of termsrv DLL to Enable Concurrent RDP via file_event

ATT&CK techniques

Lateral Movement

Recon
Resource Dev
Initial Access
Execution
Persistence
Priv Esc
Defense Evasion
Cred Access
Discovery
Lateral Movement
- T1021.001Remote Desktop Protocol
Collection
C2
Exfiltration
Impact

What it detects

This rule detects a write to the Terminal Services termsrv.dll in System32, the technique OkoBot uses to patch the RDP service and allow multiple concurrent sessions. The genuine termsrv.dll changes only through Windows servicing. An out-of-band modification indicates tampering to enable stealthy remote access.

Reporting behind it

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Malicious RDP Tunneling (via rdp)

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Malicious RDP Session Hijacking via tscon Command Line

Suspicious Replacement of termsrv DLL to Enable Concurrent RDP via file_event

Pivot detection · T1021.001 · 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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