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Ports 1883 and 8883 · TCP

Ports 1883 and 8883: MQTT (smart home)

MQTT, the messaging protocol of many smart-home and IoT devices. 8883 is the encrypted version.

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

Seeing it on your PC

Home Assistant, smart plugs and sensors talk MQTT. A broker such as Mosquitto listens on 1883.

Should you block it?

Keep a broker on your local network. Exposed brokers without a password leak everything the house reports.

Check it on your PC

Run this in PowerShell to see what is using port 1883 right now, and which program owns it:

Get-NetTCPConnection -LocalPort 1883 -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 1883,8883" -Direction Inbound -Protocol TCP -LocalPort 1883,8883 -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.