1521
Oracle Database server (TNS Listener)
Oracle Database
What is port 1521?
Port 1521 is the default port for the Oracle Database TNS (Transparent Network Substrate) Listener. Oracle DB is widely deployed in large enterprises, banks, and government agencies. When exposed to the internet it is extremely dangerous — multiple publicly known exploits exist. Always place Oracle DB behind a firewall and restrict access to trusted application servers only.
Quick checks
$
nc -zv example.com 1521
$
nmap -p 1521 example.com
$
telnet example.com 1521