Behavioral Detection of Unauthorized VNC Remote Control Sessions

Technique Detected:  VNC | T1021.005

ID: DET0178
Domains: Enterprise
Analytics: AN0504, AN0505, AN0506
Version: 1.0
Created: 21 October 2025
Last Modified: 21 October 2025

Analytics

AN0504

Detection of VNC service or executable starting unexpectedly, followed by user session creation and interactive desktop activity (mouse/keyboard simulation).

Log Sources
Data Component Name Channel
Process Creation (DC0032) WinEventLog:Sysmon EventCode=1
Logon Session Creation (DC0067) WinEventLog:Security EventCode=4624
Network Traffic Flow (DC0078) NSM:Flow port 5900 inbound
Mutable Elements
Field Description
TimeWindow Correlate VNC process with user logon activity within defined time span
VNCBinaryList Trackable VNC executable names (e.g., vncserver.exe, winvnc.exe)
LogonType Limit detection to interactive logons (type 10)

AN0505

Spawning of VNC-related processes (e.g., x11vnc, vncserver) coupled with authentication logs and port listening behavior on TCP 5900.

Log Sources
Data Component Name Channel
Process Creation (DC0032) auditd:EXECVE None
Logon Session Metadata (DC0088) linux:syslog None
Network Traffic Flow (DC0078) NSM:Flow TCP port 5900 open
Mutable Elements
Field Description
ListeningPort Default VNC port (5900) but may vary in config
ProcessNameFilter Filter specific VNC binaries in process execution logs
UserContext Scope detection to non-service or high-privilege accounts

AN0506

Detection of VNC-based remote control via screensharingd activity in Unified Logs along with concurrent remote login activity or suspicious user interaction.

Log Sources
Data Component Name Channel
Logon Session Creation (DC0067) macos:unifiedlog authentication
Process Creation (DC0032) macos:osquery process_events
Network Traffic Flow (DC0078) NSM:firewall inbound connection to port 5900
Mutable Elements
Field Description
AuthenticationPredicate Unified log predicate to refine suspicious screensharing access
TimeWindow Time between VNC connection and follow-on activity (e.g., 30s)
UserActivitySpike Mouse/keyboard interaction spike immediately post-VNC login