Port 1504 — Unassigned

Port 1504 is an unassigned port in the registered range (1024-49151). It has no official service assignment from IANA and no RFC defining what should run here.

What the Registered Range Means

Ports 1024-49151 are registered ports. Organizations can register these with IANA for specific services, but registration is optional. Many ports in this range—including 1504—remain unassigned.

This means port 1504 can be used by any application that needs it. A custom database server. An internal monitoring tool. A game server. Anything.

Known Uses

Port 1504 has no widely recognized legitimate service associated with it.

However, security databases note that port 1504 has been used by malware in the past.¹² This doesn't mean the port itself is dangerous—just that some trojans chose it as a communication channel. Unassigned ports are common targets for malware because they're less likely to conflict with legitimate services.

Checking What's Listening

If you need to see what's listening on port 1504 on your system:³

Linux/macOS:

sudo lsof -i :1504
sudo netstat -tulpn | grep 1504

Windows:

netstat -ano | findstr :1504

If something is listening and you don't recognize it, investigate. It could be a custom application you installed, or it could be something you didn't.

Why Unassigned Ports Matter

The Internet has 65,535 ports per protocol (TCP and UDP). Only a fraction are assigned to well-known services. The rest—the registered and dynamic ranges—exist for everything else.

Unassigned ports like 1504 are the working space of the Internet. They're where custom applications live, where developers test new protocols, where your video game finds a home when you host a server for friends.

They're also where malware hides when it needs a communication channel. The same flexibility that makes unassigned ports useful makes them a security concern.

The Reality of Port Numbers

Port 1504 has no story because no one claimed it. No RFC. No protocol. No service that millions depend on. It's just a number in a registry, waiting.

Most ports are like this. The famous ones—80, 443, 22—are the exception. The rest are tools. Numbers. Available when you need them.