Port 3306 (MySQL / MariaDB)

MySQL and MariaDB client connections.

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

What port 3306 is used for

MySQL and MariaDB client connections.

Security: should port 3306 be open?

Do not expose to the internet. Keep it off the internet: bind to 127.0.0.1 or a private interface (bind-address) and allow only application servers in the firewall. Exposed MySQL servers face constant brute-force attempts and ransom attacks that dump and delete databases. Use TLS for connections between hosts.

IANA assignment

Service nameProtoDescriptionAssigneeReference

mysql TCP MySQL Monty -

mysql UDP MySQL Monty -

Check what is listening on port 3306

Linux: is anything listening on TCP 3306?

sudo ss -tlnp 'sport = :3306'

Linux / macOS: which process owns the port

sudo lsof -nP -i :3306

Older Linux / BSD (net-tools)

sudo netstat -tlnp | grep ':3306 '

Windows (Command Prompt)

netstat -ano | findstr :3306

Windows (PowerShell)

Get-NetTCPConnection -LocalPort 3306 -State Listen | Select LocalAddress,OwningProcess

Test it from outside

From another machine

nc -vz -w 5 HOST 3306

From Windows

Test-NetConnection HOST -Port 3306

Block port 3306 in the firewall

ufw

sudo ufw deny 3306/tcp

iptables

sudo iptables -A INPUT -p tcp --dport 3306 -j DROP

nftables

sudo nft add rule inet filter input tcp dport 3306 drop

Windows Firewall

New-NetFirewallRule -DisplayName 'Block TCP 3306' -Direction Inbound -Protocol TCP -LocalPort 3306 -Action Block

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