Port 445 SMB · TCP

What runs on port 445

SMB over TCP: Windows file and printer sharing, Samba, and the transport for a lot of Windows administration (admin shares, PsExec, group policy). SMB 3 encrypts and signs; SMB 1 is the protocol behind WannaCry and EternalBlue and should be disabled. Internet-exposed 445 is scanned within minutes and is the single most common way ransomware enters small networks.

Software that uses it: Windows · Samba · NAS devices (Synology, QNAP, TrueNAS) · macOS file sharing

Should port 445 be open?

Private network or VPN only. Nothing good comes from this port being reachable from the internet. Keep it on an internal network, reach it over a VPN or an SSH tunnel, and firewall it from everything that does not need it.

• Never forward 445 from the internet; use a VPN. Many ISPs block it anyway.
• Disable SMBv1 (Windows: Set-SmbServerConfiguration -EnableSMB1Protocol $false; Samba: server min protocol = SMB2).
• smbclient -L host and nmap --script smb-protocols show what a server offers.

Check port 445

# on the host: is anything listening, and which process?
ss -ltnp 'sport = :445'
sudo lsof -i :445

# from another machine: is it reachable?
nc -zv host 445
nmap -p 445 host
curl -v telnet://host:445      # raw TCP connect test, Ctrl-C to leave

A port that answers from the internet when it should not is the finding; nmap from a machine outside your network (or a VPS) is the honest test, because scans from inside the LAN pass the firewall you are trying to verify.

Allow or block port 445

# ufw (Ubuntu/Debian)
sudo ufw allow from 10.0.0.0/8 to any port 445 proto tcp
sudo ufw deny 445/tcp

# nftables
nft add rule inet filter input ip saddr 10.0.0.0/8 tcp dport 445 accept
nft add rule inet filter input tcp dport 445 drop

# iptables (legacy)
iptables -A INPUT -p tcp --dport 445 -s 10.0.0.0/8 -j ACCEPT
iptables -A INPUT -p tcp --dport 445 -j DROP

# firewalld
sudo firewall-cmd --permanent --add-rich-rule='rule family=ipv4 source address=10.0.0.0/8 port port=445 protocol=tcp accept'

Replace 10.0.0.0/8 with the networks that need access. Allowing by source address is the rule that matters; "allow 445" with no source is just "open".

Related ports

• 139 NetBIOS session — Old SMB over NetBIOS
• 135 MS RPC — Windows RPC endpoint mapper
• 3389 RDP — Windows Remote Desktop
• 2049 NFS — Network file system

Part of the port number reference. Ports are 16-bit numbers; see also the subnet calculator and the packet decoder, which shows ports inside TCP and UDP headers.

Questions