Network ports · 445
445 — SMB
Port 445 carries SMB file sharing on Windows networks and must never face the internet.
Key facts
| Port | 445 |
|---|---|
| Transport | TCP |
| Service | SMB |
| Encryption | SMB 3 supports it, often optional |
| Exposure | Never expose to the public internet |
| Range | Well-known (0–1023) |
Windows file sharing
SMB provides shared folders, printers and named pipes on Windows networks. Port 445 replaced the older NetBIOS session service and is the port modern clients use. It is a rich protocol with authentication, file locking and remote procedure calls.
It is also a repeated source of critical vulnerabilities. Internet-facing SMB was the vector for WannaCry and NotPetya, which spread without user interaction once they reached an exposed host.
Keeping SMB private
Block 445 at the network edge. Share files across sites with a VPN, a document service or SFTP instead. Inside a LAN, segment the network, disable SMBv1, require signing and least-privilege accounts.
If a scan shows 445 open on a public address, treat it as an incident until proven otherwise. The service may be an appliance or a forgotten server, and either way it should not be there.
Frequently asked questions
Why is port 445 so dangerous?
It exposes a complex file-sharing service that has had remote code execution vulnerabilities, and it can spread worms across a network.
Can SMB be encrypted?
SMB 3 supports encryption, but that does not make internet exposure acceptable.