Port 139 (TCP) — NetBIOS session

Check if port 139 is open

On the server, see what is listening:

sudo ss -tulpn | grep ':139 '

From another machine, test reachability:

nc -zv your-server.example.com 139

Block port 139 from the internet

With UFW (Ubuntu/Debian):

sudo ufw deny 139

With firewalld (RHEL/AlmaLinux/Rocky):

sudo firewall-cmd --permanent --remove-port=139/tcp && sudo firewall-cmd --reload

← All common ports