Registered · Cross-platform

31337 Back Orifice / ncat

TCP Unofficial
UDP —
SCTP —
DCCP —

What it is

Back Orifice remote-admin trojan; ncat default.

When / why

Classic malware/backdoor indicator — investigate any listener.

Protocol status detail

TransportStatusMeaning
TCP Unofficial Not assigned by IANA, but standardized, specified, or widely used on this port.
UDP — Not applicable for this transport.
SCTP — Not applicable for this transport.
DCCP — Not applicable for this transport.
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Port range

Registered (1024–49151). Assigned by IANA on request; usable without elevated privileges on most systems.

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Firewall rules for port 31337

Copy-ready inbound rules for the active transports. Replace every <source> placeholder with the specific host, subnet, or CIDR that should reach this port.

⚠ High exposure risk — this service should never be reachable from untrusted networks. Scope the rule to a management subnet or VPN.

ufw

sudo ufw allow proto tcp from <source> to any port 31337

Allow TCP 31337 (Back Orifice / ncat). Replace <source> with the network/host that should reach it.

firewalld

sudo firewall-cmd --permanent --add-rich-rule='rule family="ipv4" source address="<source>" port port="31337" protocol="tcp" accept'

Allow TCP 31337 (Back Orifice / ncat) from <source>. Run 'firewall-cmd --reload' afterwards.

nftables

nft add rule inet filter input ip saddr <source> tcp dport 31337 accept

Allow TCP 31337 (Back Orifice / ncat). Assumes table 'inet filter' with an 'input' chain.

iptables

sudo iptables -A INPUT -p tcp -s <source> --dport 31337 -j ACCEPT

Allow TCP 31337 (Back Orifice / ncat). Persist with iptables-save/netfilter-persistent.

Azure NSG

az network nsg rule create -g <resource-group> --nsg-name <nsg> -n Allow-backorificencat-31337 --priority 1000 --access Allow --direction Inbound --protocol TCP --source-address-prefixes <source> --destination-port-ranges 31337

Inbound rule for 31337 (Back Orifice / ncat). Set <source> to a CIDR; lower priority number = higher precedence.

AWS Security Group

aws ec2 authorize-security-group-ingress --group-id <sg-id> --ip-permissions IpProtocol=tcp,FromPort=31337,ToPort=31337,IpRanges="[{CidrIp=<source-cidr>}]"

Inbound TCP 31337 (Back Orifice / ncat). Replace <source-cidr> (e.g. 10.0.0.0/16).

GCP firewall

gcloud compute firewall-rules create allow-backorificencat-31337 --direction=INGRESS --action=ALLOW --rules=tcp:31337 --source-ranges=<source-cidr> --network=<network>

Ingress rule for 31337 (Back Orifice / ncat). Scope with --source-ranges and optionally --target-tags.

Windows netsh

netsh advfirewall firewall add rule name="Allow Back Orifice / ncat 31337/TCP" dir=in action=allow protocol=TCP localport=31337 remoteip=<source>

Inbound TCP 31337 (Back Orifice / ncat). Set remoteip to a host/subnet; 'any' is discouraged.

Windows PowerShell

New-NetFirewallRule -DisplayName "Allow Back Orifice / ncat 31337/TCP" -Direction Inbound -Action Allow -Protocol TCP -LocalPort 31337 -RemoteAddress <source>

Inbound TCP 31337 (Back Orifice / ncat). Replace <source> with a host or subnet.

Rules are generated only for transports marked active for this port. They default to an inbound allow with an explicit source placeholder — never any. Review direction, scope, and rule precedence before applying in production.