445
Windows file and printer sharing (SMB)
Server Message Block / Microsoft-DS
What is port 445?
SMB (Server Message Block) on port 445 is the Windows protocol for shared network drives, printers, and inter-process communication. It is also used by Samba on Linux and macOS. It is one of the most dangerous ports to expose to the internet: the NSA's EternalBlue exploit targeting port 445 was weaponized by WannaCry in 2017, infecting hundreds of thousands of systems worldwide. This port must ALWAYS be blocked at the internet perimeter.
Quick checks
$
nc -zv example.com 445
$
nmap -p 445 example.com
$
telnet example.com 445