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Port 4366 (shadowstream)

IANA assigns port 4366 to shadowstream: ShadowStream System.

Registered (user) port, 1024-49151 UDP

Port 4366 is normally used over UDP; the checker tests TCP only, so a "filtered" result does not mean the UDP service is down.

IANA assignment

Service nameProtoDescriptionAssigneeReference
shadowstream UDP ShadowStream System StorageCraft Technology Corporation -

Registry dates for this port: registered 2014-12-17.

Check what is listening on port 4366

Linux: UDP 4366
sudo ss -ulnp 'sport = :4366'
Linux / macOS: which process owns the port
sudo lsof -nP -i :4366
Windows (Command Prompt)
netstat -ano | findstr :4366
Windows (PowerShell)
Get-NetUDPEndpoint -LocalPort 4366

Test it from outside

UDP probe (no reply does not prove it is closed)
nc -vzu -w 5 HOST 4366

Block port 4366 in the firewall

ufw
sudo ufw deny 4366/udp
iptables
sudo iptables -A INPUT -p udp --dport 4366 -j DROP
nftables
sudo nft add rule inet filter input udp dport 4366 drop
Windows Firewall
New-NetFirewallRule -DisplayName 'Block UDP 4366' -Direction Inbound -Protocol UDP -LocalPort 4366 -Action Block

Related ports

4361nacnl4362afore-vdp-disc4368wxbrief4369Erlang Port Mapper (EPMD)

All port numbers · Open port checker
Assignment data: IANA port number registry (public domain), retrieved 2026-11-10.