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Port 5423 (virtualuser)

IANA assigns port 5423 to virtualuser: VIRTUALUSER.

Registered (user) port, 1024-49151 TCPUDP

IANA assignment

Service nameProtoDescriptionAssigneeReference
virtualuser TCP VIRTUALUSER Chad Williams -
virtualuser UDP VIRTUALUSER Chad Williams -

Check what is listening on port 5423

Linux: is anything listening on TCP 5423?
sudo ss -tlnp 'sport = :5423'
Linux: UDP 5423
sudo ss -ulnp 'sport = :5423'
Linux / macOS: which process owns the port
sudo lsof -nP -i :5423
Older Linux / BSD (net-tools)
sudo netstat -tlnp | grep ':5423 '
Windows (Command Prompt)
netstat -ano | findstr :5423
Windows (PowerShell)
Get-NetTCPConnection -LocalPort 5423 -State Listen | Select LocalAddress,OwningProcess

Test it from outside

From another machine
nc -vz -w 5 HOST 5423
From Windows
Test-NetConnection HOST -Port 5423
UDP probe (no reply does not prove it is closed)
nc -vzu -w 5 HOST 5423

Block port 5423 in the firewall

ufw
sudo ufw deny 5423/tcp
iptables
sudo iptables -A INPUT -p tcp --dport 5423 -j DROP
nftables
sudo nft add rule inet filter input tcp dport 5423 drop
Windows Firewall
New-NetFirewallRule -DisplayName 'Block TCP 5423' -Direction Inbound -Protocol TCP -LocalPort 5423 -Action Block
ufw
sudo ufw deny 5423/udp
iptables
sudo iptables -A INPUT -p udp --dport 5423 -j DROP
nftables
sudo nft add rule inet filter input udp dport 5423 drop
Windows Firewall
New-NetFirewallRule -DisplayName 'Block UDP 5423' -Direction Inbound -Protocol UDP -LocalPort 5423 -Action Block

Related ports

5421netsupport25422salient-mux5424beyond-remote5425br-channel

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