BRev Port 8080 — HTTP alternate
Port 8080 exists because of a Unix rule: only root can bind a port below 1024. Application servers that wanted to run as an unprivileged user picked the visually obvious “80, but higher”, and it stuck. Tomcat, Jetty, Jenkins, JBoss/WildFly, Spring Boot, many Docker images and almost every reverse-proxy backend default to it, which is why the answer to “what runs on 8080” is genuinely “whichever of those you installed most recently”.
That ambiguity is the security problem. Our reference marks it care: a real service behind a reverse proxy on 8080 is entirely normal, but the same port hosting a bare Jenkins, an open forward proxy or a container management UI is a takeover. Jenkins in particular runs builds, which means arbitrary code execution is its designed feature — an unauthenticated Jenkins on a public 8080 is a compromised host, not a misconfiguration to schedule.
The other recurring mistake is leaving 8080 reachable alongside the proxy. A typical deployment puts nginx on 443 with TLS, authentication and rate limiting, forwarding to the app on 8080 — and then never firewalls 8080 itself, so anyone can bypass every one of those controls by adding a port to the URL. Bind the backend to 127.0.0.1, not 0.0.0.0.
Port 8080 at a glance
| Field | Value | Detail |
|---|---|---|
| Port | 8080 | Registered |
| Service | HTTP alt / proxy | The classic alternate web port — Tomcat, Jenkins, proxies. (TCP) |
| Category | Web | HTTP(S) and things browsers speak |
| Exposure | Care | Expose with care |
Should port 8080 face the internet? Fine for a real service behind a reverse proxy; a naked Jenkins or an open proxy here is a takeover.
Legitimately public in some setups, but only hardened — current version, real authentication, rate limits, and ideally an allow-list.
What commonly goes wrong
“Address already in use” on 8080
Something is already there, and on a developer machine that is usually a previous run of the same app that did not exit, a Docker container still publishing the port, or a second JVM. The local commands on this page print the PID holding it; kill that rather than picking 8081, or you will accumulate half-dead servers all week.
The proxy is secured and the app is still reachable directly
Because the backend is bound to 0.0.0.0 and the port is open. Every control you put in the proxy — TLS, auth, rate limits, WAF rules — is bypassed by requesting host:8080 directly. Bind the application to 127.0.0.1 (or a private container network) and let only the proxy reach it.
Check port 8080 yourself
No browser can open a raw TCP socket, so no web page can honestly tell you whether this port is open on a remote host. These are the real commands, generated for port 8080 — swap example.com for the host you are actually testing.
What on this machine is holding port 8080?
sudo ss -tlnp | grep :8080Lists the listening socket and the PID/program holding it. Drop sudo and you get the socket but not the process name.
sudo lsof -i :8080The macOS answer to "address already in use". Kill it with `kill -9 <PID>` once you are sure what it is.
netstat -ano | findstr :8080The last column is the PID. Match it in Task Manager’s Details tab, or `taskkill /PID <pid> /F`.
Is port 8080 reachable on another host?
nc -vz example.com 8080"succeeded!" means the TCP handshake completed — the port is open. "Connection refused" is closed; a hang until timeout means filtered (a firewall dropped it silently).
nmap -Pn -p 8080 example.comThe only common tool that distinguishes open / closed / filtered. -Pn skips the ping sweep, so it still works against hosts that ignore ICMP.
Test-NetConnection example.com -Port 8080Read TcpTestSucceeded: True = open. It is built in — nothing to install.
telnet example.com 8080A blank screen or a banner means it connected. "Connection refused" means closed. Quit with Ctrl-] then `quit`.
curl -v --max-time 5 telnet://example.com:8080Handy when telnet is not installed: "Connected to …" proves the TCP handshake, without curl trying to speak HTTP.
No web page can tell you whether a port is open on a remote host
A browser cannot open a raw TCP socket — there is no API for it, by design. So a site that reports “port 3389 is OPEN on 203.0.113.10” is not checking from your browser; it is asking its own server to scan on your behalf. That works, but it means their server sees the host you asked about, scans from their address rather than yours, and answers a question about their network path, not yours.
We don't have a server here and won't pretend to. So this page does three honest things instead:
| Port | Proto | Service | What it is | Exposure | |
|---|---|---|---|---|---|
| 8080 | tcp | HTTP alt / proxy | The classic alternate web port — Tomcat, Jenkins, proxies.Fine for a real service behind a reverse proxy; a naked Jenkins or an open proxy here is a takeover. | Care |
http://host:port/ and times it. A connection that is established proves a socket is open; an instant refusal usually means nothing is listening; anything else is honestly reported as “can't tell”. Each attempt gives up after 2.5s.nc -vz example.com 443
nmap -Pn -p 443 example.com
telnet example.com 443
curl -v --max-time 5 telnet://example.com:443
This page cannot answer that, and neither can any other page — from your browser. Opening a TCP connection to an arbitrary host and port is not something JavaScript is allowed to do. Every “open port checker” that gives you a green tick is running the scan on their server. Which is fine, as long as you know what you are agreeing to: they learn which host and port you were worried about, and the answer they give you is about the route from their data centre — not from the internet as your users see it.
What to do instead
Run the check from outside your own network. Copy an nmap or nc line from the card above and run it from a machine that is not behind the same router — a phone on mobile data with a terminal app, a cheap VPS, a colleague's laptop. Running it from inside the LAN tests the LAN, not the internet, and will happily say “open” while the world sees nothing.
Then check the thing that is actually blocking it, in this order: the service is bound to0.0.0.0 and not 127.0.0.1 · the host firewall (ufw, firewalld, Windows Defender Firewall) · the cloud security group or the router's port-forward rule · and finally your ISP, which commonly blocks 25, 80 and 445 on residential lines whatever you configure.
What a browser genuinely can verify
One thing: that an HTTPS service answers. If what you actually want to know is “is my site up and how fast is it”, the latency test measures real round trips to a CORS-open URL. If the name doesn't resolve, or resolves somewhere unexpected, that is a DNS problem, not a port problem — and it is the more common cause of “my port is closed” than an actual firewall.
An IP address finds the machine; a port picks which program on it gets the traffic. TCP sets up a connection first — a handshake, ordered delivery, retransmission — which is why the web, email and SSH use it. UDP just sends the packet with no handshake and no guarantee it arrives, which is why DNS, video calls and games use it: late data is worse than lost data.
That difference is why a UDP port is so much harder to test. TCP either completes a handshake or it doesn't, so a tool can tell you. A UDP service that has nothing to say to an unexpected packet stays silent — and silence looks identical to a firewall dropping it.
The three ranges
0–1023Assigned by IANA to core services. On Unix, binding one needs root (or CAP_NET_BIND_SERVICE).1024–49151Registered by vendors for their applications. Any user can bind these — which is why every dev server lives here.49152–65535Never assigned. The OS hands these out as the SOURCE port of your outgoing connections. (Linux actually uses 32768–60999 by default.)Closed is not the same as filtered
Closed means the host answered: the packet arrived, nothing is listening, and you got an immediate refusal (a TCP RST). Filtered means nothing answered at all — a firewall dropped your packet in silence, so you wait for a timeout and learn nothing. The difference matters: closed proves the host is reachable and the port is free; filtered tells you only that something between you and it is discarding traffic.nmap reports the two separately. A browser cannot distinguish them, which is why this page reports a timeout as “can't tell” rather than guessing.
The one habit worth keeping
Bind services to 127.0.0.1 instead of 0.0.0.0 unless something outside the machine genuinely needs them, and reach them over SSH or a VPN. Every database on the never-expose list above ships with that advice, and the leaks all begin the same way: a default bind address, a cloud instance with a public IP, and a scanner that found it within the hour.
The blocked-port list this page uses is the WHATWG Fetch Standard's “bad port” table — the ports every browser refuses to connect to (Chrome calls it ERR_UNSAFE_PORT). Local probing is additionally gated by Chrome's Local Network Access permission, which replaced Private Network Access and ships in Chrome 142.
FAQ
Is port 8080 the same as port 80?
Only by convention. It is an ordinary unprivileged port that people use for HTTP; nothing in any browser or protocol treats it specially, so URLs need the port explicitly. It is not encrypted by default either — 8443 is the usual TLS counterpart.
Is it safe to expose port 8080?
It depends entirely on what is behind it. A patched, authenticated application is as safe as it would be on 443 — put TLS in front of it. A dev server, a Jenkins, an open proxy or an admin console is not, and those are the common cases.
What is using port 8080 on my machine?
Run the local command for your platform on this page — ss on Linux, lsof on macOS, netstat -ano plus tasklist on Windows. Each one names the process, which is the only reliable answer.