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// IoT & industrial (ICS)

Port 8883: MQTT over TLS

MQTT over TLS.

8883

How MQTT over TLS works

IoT & industrial (ICS)
producerconsumerqueuePUBLISH producerconsumerqueuePUBLISH

Producers publish messages into a queue on port 8883; consumers pick them up in order, at their own pace. Everything is encrypted: someone on the path only sees unreadable bytes.

Transport
TCP · UDP
Exposure risk
4/10 moderate if reachable from the Internet
Encryption
EncryptedTLS or built-in crypto
IANA status
Assigned1 registered service
Range
Registered (1024-49151)
Category
IoT & industrial (ICS)
01 Security

Is port 8883 dangerous?

Common attacks and weaknesses

  • Weak device credentials shared across fleets.

How to secure it

  • Use per-device client certificates.
02 Registry

IANA registry entries for port 8883

ServicePortTransportDescriptionReferenceUpdated
secure-mqtt 8883 TCP, UDP Secure MQTT - 2015-03-06

// source: IANA service name and port number registry

03 Check it

Which program uses port 8883, and is it reachable?

Linux

sudo ss -ltnup 'sport = :8883'      # process listening on 8883
sudo lsof -nP -i :8883

macOS

sudo lsof -nP -i :8883

Windows (PowerShell)

Get-NetTCPConnection -LocalPort 8883 -State Listen | Select LocalAddress, OwningProcess
Get-NetUDPEndpoint -LocalPort 8883
netstat -ano | findstr :8883

From another machine

nmap -p 8883 -sV <host>
sudo nmap -sU -p 8883 <host>
nc -zv <host> 8883

Block it in the firewall

sudo ufw deny 8883/tcp                                         # Linux (ufw)
New-NetFirewallRule -DisplayName "Block 8883" -Direction Inbound -LocalPort 8883 -Protocol TCP -Action Block  # Windows
04 FAQ
What is port 8883 used for?

MQTT over TLS.

Is port 8883 TCP or UDP?

Port 8883 is registered for TCP and UDP. In practice the service mostly uses TCP.

Is it safe to open port 8883?

It is rated 4/10 (moderate) when exposed to the Internet. Weak device credentials shared across fleets. Use per-device client certificates.

How do I check if port 8883 is open?

On Linux run "ss -ltnup 'sport = :8883'", on macOS "lsof -nP -i :8883", and on Windows "netstat -ano | findstr :8883" to see the local process. From another machine, "nmap -p 8883 <host>" shows whether it is reachable.

05 Related
:1883 MQTT tcp · udp · high risk :502 Modbus TCP tcp · udp · critical risk :102 Siemens S7 (ISO-TSAP) tcp · udp · critical risk :47808 BACnet udp · tcp · critical risk :20000 DNP3 tcp · udp · sctp · critical risk :44818 EtherNet/IP tcp · udp · critical risk :802 Modbus Application Protocol Secure tcp · udp :2221 EtherNet/IP over TLS tcp · udp

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