Port 445 — SMB

Security guidance

The vector for WannaCry and countless ransomware outbreaks. It must never be reachable from the internet, and most ISPs block it anyway.

Test port 445 yourself

From your own machine, against any host (swap in your domain):

macOS / Linux — netcat

nc -vz example.com 445

Any OS — nmap

nmap -p 445 example.com

Windows — PowerShell

Test-NetConnection example.com -Port 445

open = a service answered on port 445; closed = the host replied but nothing is listening; filtered = a firewall silently dropped the probe. These test from your network — our port checker tests from the outside, the view that matters for security.

Other common ports