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Port 5900 · TCP

Port 5900: VNC (remote control)

Virtual Network Computing, remote control of a desktop (TightVNC, RealVNC, UltraVNC and others).

Protocol
TCP
On Windows
Not part of Windows; installed software uses it
Risk if open to the internet
High

Seeing it on your PC

A listener on 5900 means a VNC server is installed.

Should you block it?

Many VNC setups use weak or no passwords and send the screen unencrypted. Never expose 5900 to the internet; use it over a VPN.

Check it on your PC

Run this in PowerShell to see what is using port 5900 right now, and which program owns it:

Get-NetTCPConnection -LocalPort 5900 -ErrorAction SilentlyContinue | Select-Object LocalAddress,LocalPort,RemoteAddress,RemotePort,State,@{n='Process';e={(Get-Process -Id $_.OwningProcess -ErrorAction SilentlyContinue).ProcessName}}

No output means nothing is using the port at the moment. For every connection at once, paste netstat -ano into the netstat explainer.

Block it in Windows Firewall

In PowerShell run as administrator, this stops other computers from connecting to this port on your PC. It does not stop your own programs connecting out.

New-NetFirewallRule -DisplayName "Block inbound TCP 5900" -Direction Inbound -Protocol TCP -LocalPort 5900 -Action Block

Undo it with Remove-NetFirewallRule -DisplayName "Block inbound …", using the same name. If you depend on the service on your local network, this rule stops that too.