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// Web

Port 20003: Commtact HTTPS

Port 20003 is assigned by IANA to commtact-https (Commtact HTTPS).

20003

How commtact-https works

Web
browser:20003commtact-https browser:20003commtact-https

A browser sends an HTTP request to port 20003 and the commtact-https server sends the page back.

Transport
TCP · UDP
Exposure risk
not rated depends on the program listening
Encryption
Unknownnot stated by the registry
IANA status
Assigned1 registered service
Range
Registered (1024-49151)
Category
Web
01 Security

Is port 20003 dangerous?

We have no specific security note for port 20003. Its risk depends on the program actually listening on it. General advice for web services:

  • Serve it over HTTPS only and check the HTTP security headers.
  • Keep admin consoles and development servers off the Internet.
  • Patch the application server and remove default credentials and sample apps.
02 Registry

IANA registry entries for port 20003

ServicePortTransportDescriptionReferenceUpdated
commtact-https 20003 TCP, UDP Commtact HTTPS - 2004-12

// source: IANA service name and port number registry

03 Check it

Which program uses port 20003, and is it reachable?

Linux

sudo ss -ltnup 'sport = :20003'      # process listening on 20003
sudo lsof -nP -i :20003

macOS

sudo lsof -nP -i :20003

Windows (PowerShell)

Get-NetTCPConnection -LocalPort 20003 -State Listen | Select LocalAddress, OwningProcess
Get-NetUDPEndpoint -LocalPort 20003
netstat -ano | findstr :20003

From another machine

nmap -p 20003 -sV <host>
sudo nmap -sU -p 20003 <host>
nc -zv <host> 20003

Block it in the firewall

sudo ufw deny 20003/tcp                                         # Linux (ufw)
New-NetFirewallRule -DisplayName "Block 20003" -Direction Inbound -LocalPort 20003 -Protocol TCP -Action Block  # Windows
04 FAQ
What is port 20003 used for?

Port 20003 is assigned by IANA to commtact-https (Commtact HTTPS).

Is port 20003 TCP or UDP?

Port 20003 is registered for TCP and UDP.

Is it safe to open port 20003?

It depends on the program that listens on it. Open it only for a service you know and only to the networks that need it. Serve it over HTTPS only and check the HTTP security headers.

How do I check if port 20003 is open?

On Linux run "ss -ltnup 'sport = :20003'", on macOS "lsof -nP -i :20003", and on Windows "netstat -ano | findstr :20003" to see the local process. From another machine, "nmap -p 20003 <host>" shows whether it is reachable.

05 Related
:443 HTTPS tcp · udp · sctp · low risk :80 HTTP tcp · udp · sctp · moderate risk :8080 HTTP alternate tcp · udp · high risk :8443 HTTPS alternate tcp · udp · moderate risk :3000 Dev servers / Grafana tcp · udp · moderate risk :5000 Flask / Docker registry / UPnP tcp · udp · moderate risk :8000 HTTP alternate (dev) tcp · udp · moderate risk :8888 Jupyter / HTTP alternate tcp · udp · high risk

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