Port 5000 dev servers · TCP

What runs on port 5000

Shared by far too many things: Flask's development server, the Docker registry, Synology DSM (5000/5001), UPnP on some devices, .NET's Kestrel default (5000/5001), and macOS AirPlay Receiver, which since Monterey occupies 5000 on Macs and breaks every Flask tutorial. On a server, find out which one you have before opening anything.

Software that uses it: Flask (dev server) · Docker registry (registry:2) · Synology DSM · ASP.NET Core Kestrel · macOS AirPlay Receiver · UPnP/DLNA on some devices

Should port 5000 be open?

Loopback or the host's own network only. The service should listen on 127.0.0.1 (or a Unix socket) and be reached by a reverse proxy or by the application on the same host. If it answers on a public address, that is a misconfiguration.

• On macOS: System Settings → General → AirDrop & Handoff → AirPlay Receiver off, or run Flask on another port.
• A Docker registry on 5000 without TLS and auth lets anyone push images that your servers will pull.

Check port 5000

# on the host: is anything listening, and which process?
ss -ltnp 'sport = :5000'
sudo lsof -i :5000

# from another machine: is it reachable?
nc -zv host 5000
nmap -p 5000 host
curl -v telnet://host:5000      # raw TCP connect test, Ctrl-C to leave

A port that answers from the internet when it should not is the finding; nmap from a machine outside your network (or a VPS) is the honest test, because scans from inside the LAN pass the firewall you are trying to verify.

Allow or block port 5000

# ufw (Ubuntu/Debian)
sudo ufw allow from 10.0.0.0/8 to any port 5000 proto tcp
sudo ufw deny 5000/tcp

# nftables
nft add rule inet filter input ip saddr 10.0.0.0/8 tcp dport 5000 accept
nft add rule inet filter input tcp dport 5000 drop

# iptables (legacy)
iptables -A INPUT -p tcp --dport 5000 -s 10.0.0.0/8 -j ACCEPT
iptables -A INPUT -p tcp --dport 5000 -j DROP

# firewalld
sudo firewall-cmd --permanent --add-rich-rule='rule family=ipv4 source address=10.0.0.0/8 port port=5000 protocol=tcp accept'

Replace 10.0.0.0/8 with the networks that need access. Allowing by source address is the rule that matters; "allow 5000" with no source is just "open".

Putting it behind nginx

server {
    listen 443 ssl;
    server_name app.example.com;
    location / {
        proxy_pass http://127.0.0.1:5000;
        proxy_set_header Host $host;
        proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
        proxy_set_header X-Forwarded-Proto https;
    }
}

Then make the application listen on 127.0.0.1:5000 only. Test which location block a request hits with the nginx location tester.

Related ports

• 3000 dev servers — Grafana, Rails, Node apps
• 8000 dev servers — Django, python -m http.server
• 5001 DSM (TLS) / iperf3
• 5173 Vite dev

Part of the port number reference. Ports are 16-bit numbers; see also the subnet calculator and the packet decoder, which shows ports inside TCP and UDP headers.

Questions