Port 1521 (Oracle Database listener)

Oracle TNS listener for database connections.

Registered (user) port, 1024-49151 TCP Databases Do not expose to the internet

What port 1521 is used for

Oracle TNS listener for database connections.

Security: should port 1521 be open?

Do not expose to the internet. Keep internal. Exposed listeners leak version and SID information and face password-guessing against default accounts.

IANA assignment

Service nameProtoDescriptionAssigneeReference

ncube-lm TCP nCube License Manager Maxine Yuen -

ncube-lm UDP nCube License Manager Maxine Yuen -

Registry dates for this port: last modified 2022-02-14.

Check what is listening on port 1521

Linux: is anything listening on TCP 1521?

sudo ss -tlnp 'sport = :1521'

Linux / macOS: which process owns the port

sudo lsof -nP -i :1521

Older Linux / BSD (net-tools)

sudo netstat -tlnp | grep ':1521 '

Windows (Command Prompt)

netstat -ano | findstr :1521

Windows (PowerShell)

Get-NetTCPConnection -LocalPort 1521 -State Listen | Select LocalAddress,OwningProcess

Test it from outside

From another machine

nc -vz -w 5 HOST 1521

From Windows

Test-NetConnection HOST -Port 1521

Block port 1521 in the firewall

ufw

sudo ufw deny 1521/tcp

iptables

sudo iptables -A INPUT -p tcp --dport 1521 -j DROP

nftables

sudo nft add rule inet filter input tcp dport 1521 drop

Windows Firewall

New-NetFirewallRule -DisplayName 'Block TCP 1521' -Direction Inbound -Protocol TCP -LocalPort 1521 -Action Block

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Assignment data: IANA port number registry (public domain), retrieved 2026-11-10.