Port 1904 has no officially assigned service. IANA — the Internet Assigned Numbers Authority, which manages the global port registry — lists it as unassigned.1
That doesn't mean nothing uses it. It means nothing is supposed to.
The Registered Port Range
Port 1904 falls in the registered port range (1024–49151). This range sits between the well-known ports (0–1023), which are reserved for foundational protocols like HTTP, SSH, and DNS, and the ephemeral ports (49152–65535), which operating systems assign temporarily to outgoing connections.
The registered range is where applications go to stake a claim. A company building a database, a game developer needing a multiplayer port, an enterprise software vendor — they submit a request to IANA, get a port assigned, and that port becomes theirs in the registry. Thousands of ports in this range have legitimate owners.
Port 1904 never got one.
Known Unofficial Uses
Port databases flag 1904 with a historical malware association. A trojan identified as using kgiloa.exe was observed communicating on port 1904.2 This doesn't mean the port is dangerous — it means an attacker once chose this quiet, unassigned address precisely because nothing legitimate lived there. An unassigned port draws less attention than, say, something knocking on port 80.
The flag lives on in security databases as a caution, not a condemnation. The port did nothing wrong.
No documented legitimate application claims port 1904 as a standard.
How to Check What's Listening on This Port
If you see activity on port 1904 and want to know what's causing it:
On Linux or macOS:
On Windows:
The process ID in the output will tell you exactly which application opened the port. From there, check the process name in Task Manager or with ps aux | grep <PID> on Linux.
Why Unassigned Ports Exist
The port space has 65,535 slots. Many thousands are assigned; thousands more sit empty, unclaimed. IANA doesn't pre-populate the registry — it fills in as applications need permanent, documented homes.
Unassigned ports aren't wasted space. They're the address system working as designed: space held in reserve, available when something real needs it. Until then, they're quiet. Which is exactly why attackers and developers alike occasionally choose them — quiet neighborhoods attract less scrutiny.
Port 1904 is available. Whether that's an opportunity or a warning depends entirely on what shows up.
Frequently Asked Questions
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