Port 445 (SMB) — What It Is and How to Use It

Port 445 is the primary port used by the Server Message Block (SMB) protocol, which provides file sharing, printer sharing, and inter-process communication over a network. It's crucial for network functionality in Windows environments and increasingly in other operating systems as well, enabling resource access and management across devices.

Last updated: 2026-03-02

                Port Number
                445
            

Protocol SMB

Common Use Cases

File sharing between Windows computers
Printer sharing on a network
Domain authentication and Active Directory services

Check if Port 445 is Open

nmap -p 445 <target_ip>

Test-NetConnection -ComputerName <target_ip> -Port 445

⚠️ Security Note: Port 445 is a frequent target for malware and ransomware attacks, such as WannaCry, making it critical to secure and monitor. Leaving it exposed to the internet can allow unauthorized access to shared resources and system compromise.

Related Ports

Frequently Asked Questions

Is port 445 dangerous to leave open?

Yes, leaving port 445 open to the internet is highly dangerous. It allows potential attackers to attempt to exploit vulnerabilities in the SMB protocol, potentially leading to data breaches, ransomware infections, and complete system compromise. It should be firewalled off from the public internet.

What service uses port 445?

Port 445 is primarily used by the Server Message Block (SMB) protocol, specifically the direct TCP transport of SMB (SMB over TCP). This allows SMB to function without relying on NetBIOS.