# WHATPORT(1521)

## NAME

port 1521 — Oracle Database listener (TNS) — The Oracle Net listener — the front door to an Oracle database, squatting on a registration for something else entirely.

Protocol: TCP  
IANA registry

## DESCRIPTION

Oracle's listener process accepts TNS (Transparent Network Substrate) connections on TCP 1521 by default; the database's PMON registers its services with the listener there, and every sqlplus, JDBC thin, and OCI client connects through it. IANA never assigned 1521 to Oracle — the registry still reads "ncube-lm", the nCube License Manager — Oracle simply took the port and the world followed. A TNS listener will answer a version query before you authenticate, and older ones would dump their whole service list to an unauthenticated `lsnrctl status`. On a scan it means a database server, an Oracle E-Business/PeopleSoft tier, or an appliance that embedded Oracle XE.

## EXPOSURE

**Do not expose.** This is a database's authentication surface with the entire dataset behind it, and TNS has a long CVE history including listener poisoning — bind it to a private interface and reach it over a VPN or SSH tunnel.

## CHECK

```sh
nmap -sV -p 1521 TARGET
```

## SEE ALSO

- docs — [Oracle Database Net Services Reference — Protocol Address Configuration (default port 1521)](https://docs.oracle.com/en/database/oracle/oracle-database/19/netrf/protocol-address-configuration.html) (docs.oracle.com)
- iana — [IANA port registry — 1521 (registered as ncube-lm, not Oracle)](https://www.iana.org/assignments/service-names-port-numbers/service-names-port-numbers.xhtml?search=1521) (iana.org)

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HTML: <https://whatport.net/1521/> · JSON: <https://whatport.net/1521.json> · full dataset: <https://whatport.net/ports.json>