Port 445 — SMB
Quick reference for TCP/UDP port 445, used by SMB. Includes what the service does, security guidance and related ports.
What is port 445?
Windows file sharing. Block on the WAN — exploited by EternalBlue / WannaCry.
What port does SMB use?
SMB listens on port 445 by default.
Is port 445 open? How to check
Run one of these from your computer, replacing HOST with the IP address or domain you want to test.
nc -zv HOST 445
Test-NetConnection HOST -Port 445
nmap -p 445 HOST
A refused or timed-out connection means the port is closed or filtered by a firewall.
Security guidance
High risk — do not expose to the internet
Port 445 (SMB) is high-risk because the service it carries is a frequent target for credential attacks, brute force or unpatched-vulnerability scanning. Keep it bound to localhost or your VPN, never forward it directly on a router, and require strong authentication.
Related ports
Frequently asked
What is port 445 used for?+
Port 445 is the standard TCP/UDP port for SMB. Windows file sharing. Block on the WAN — exploited by EternalBlue / WannaCry.
What port does SMB use?+
SMB listens on port 445 by default.
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