Port 31337 (Back Orifice / 'eleet')

Not assigned by IANA. Historically the port of the Back Orifice trojan (1998); now mostly a joke port used in CTFs and demos.

Registered (user) port, 1024-49151 TCPUDP Security Do not expose to the internet

What port 31337 is used for

Not assigned by IANA. Historically the port of the Back Orifice trojan (1998); now mostly a joke port used in CTFs and demos.

Do not expose to the internet. Unexpected listeners on 31337 are worth investigating.

Service nameProtoDescriptionAssigneeReference

eldim TCP eldim is a secure file upload proxy Antonios A Chariton -

eldim UDP eldim is a secure file upload proxy Antonios A Chariton -

Registry dates for this port: registered 2021-05-14.

Linux: is anything listening on TCP 31337?

sudo ss -tlnp 'sport = :31337'

Linux: UDP 31337

sudo ss -ulnp 'sport = :31337'

Linux / macOS: which process owns the port

sudo lsof -nP -i :31337

Older Linux / BSD (net-tools)

sudo netstat -tlnp | grep ':31337 '

Windows (Command Prompt)

netstat -ano | findstr :31337

Windows (PowerShell)

Get-NetTCPConnection -LocalPort 31337 -State Listen | Select LocalAddress,OwningProcess

From another machine

nc -vz -w 5 HOST 31337

From Windows

Test-NetConnection HOST -Port 31337

UDP probe (no reply does not prove it is closed)

nc -vzu -w 5 HOST 31337

ufw

sudo ufw deny 31337/tcp

iptables

sudo iptables -A INPUT -p tcp --dport 31337 -j DROP

nftables

sudo nft add rule inet filter input tcp dport 31337 drop

Windows Firewall

New-NetFirewallRule -DisplayName 'Block TCP 31337' -Direction Inbound -Protocol TCP -LocalPort 31337 -Action Block

ufw

sudo ufw deny 31337/udp

iptables

sudo iptables -A INPUT -p udp --dport 31337 -j DROP

nftables

sudo nft add rule inet filter input udp dport 31337 drop

Windows Firewall

New-NetFirewallRule -DisplayName 'Block UDP 31337' -Direction Inbound -Protocol UDP -LocalPort 31337 -Action Block

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Assignment data: IANA port number registry (public domain), retrieved 2026-11-10.