What is port 445 used for?

Port 445 is the standard TCP port used for SMB / CIFS (Windows File Sharing). It is commonly used by Windows File Sharing (LanmanServer), Samba (Linux). Server Message Block protocol providing shared access to files, printers, and serial ports.

How do I check if port 445 is open?

Enter your public IP or hostname into the scanner tool and click Check. A sub-second raw TCP socket handshake will be initiated from our edge server to port 445 on your target. If the 3-way handshake finishes with SYN-ACK, the port is OPEN. If an RST packet is returned, the host is reachable but the port is CLOSED. If packets time out without response, the port is FILTERED by an ISP or firewall.

Why does port 445 show as closed or filtered?

Residential internet service providers (ISPs) often block inbound connections on port 445 by default to prevent spam, botnets, or unauthorized server hosting. If the scanner reports FILTERED, verify your router port forwarding configuration and confirm with your ISP whether inbound port 445 is restricted.

PORT 445 TCP File Transfer Critical Risk

Port 445 (SMB / CIFS (Windows File Sharing)) Open Check

Q: Is port 445 safe to expose to the public internet?

Exposing port 445 carries elevated security risks (Critical risk). Severe danger. Direct internet exposure of SMB is universally targeted by wormable exploits (EternalBlue, WannaCry). Blocked by virtually all ISPs. For remote services, consider placing them behind a secure VPN (such as WireGuard or Tailscale) or restricting inbound access with strict IP firewall rules.

Server Message Block protocol providing shared access to files, printers, and serial ports.

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Port Specifications & Network Behavior

Standard Port Number 445

Primary Service SMB / CIFS (Windows File Sharing)

Transport Protocol TCP

Traffic Classification File Transfer

Residential ISP Status Commonly filtered/blocked by residential ISPs

Security Exposure Critical Exposure discouraged without VPN or firewall protection

Security Advisory: SMB / CIFS (Windows File Sharing) (Port 445)

Severe danger. Direct internet exposure of SMB is universally targeted by wormable exploits (EternalBlue, WannaCry). Blocked by virtually all ISPs.

Recommendation: Keep port 445 closed to WAN traffic. Connect remotely using WireGuard, Tailscale, or an SSH tunnel.

Port Forwarding & Troubleshooting Checklist

If port 445 returns CLOSED or FILTERED, work through this verified diagnostic checklist:

1 Do NOT forward port 445 to the public internet.
2 To access shared drives remotely, connect through WireGuard VPN (port 51820) or Tailscale.
3 If testing internal LAN connectivity, ensure Windows 'File and Printer Sharing' is allowed in private network firewall.

Verify Host Is Listening Locally

Windows (PowerShell) netstat -ano | findstr :445

Linux / macOS (Bash) ss -tulpn | grep :445