VNC:
Persistence
Guides on maintaining access via reverse VNC callbacks
VNC persistence installs a remote desktop channel that survives reboots and user sessions. A hidden VNC server (x11vnc, TightVNC, or UltraVNC) configured to start at boot gives you graphical access whenever you need it. On Linux, add it as a systemd service or drop it in rc.local. On Windows, install it as a system service through the installer's silent mode or manual registry entries.
Reverse VNC connections flip the model so the target connects out to you, bypassing inbound firewall rules. Configure the VNC server with the -connect flag pointing to your listener, triggered by a scheduled task or cron job. This approach also avoids opening an additional listening port on the target.
Registry-based autostart on Windows (HKLM\SOFTWARE\Microsoft\Windows\CurrentVersion\Run) ensures the VNC server launches with every boot. For stealth, use a non-standard port, disable the tray icon, set a password you control, and name the binary something that blends with legitimate services. Combine VNC persistence with SSH tunneling to encrypt the traffic and reduce detection signatures.