Description

Configure the loopback interface to accept traffic. Configure all other interfaces to deny traffic to the loopback network.

Rationale

Loopback traffic is generated between processes on machine and is typically critical to operation of the system. The loopback interface is the only place that loopback network traffic should be seen, all other interfaces should ignore traffic on this network as an anti-spoofing measure.

Remediation

Shell script

The following script can be run on the host to remediate the issue.

#!/bin/bash

# Remediation is applicable only in certain platforms
if dpkg-query --show --showformat='${db:Status-Status}
' 'kernel' 2>/dev/null | grep -q installed && { dpkg-query --show --showformat='${db:Status-Status}\n' 'ufw' 2>/dev/null | grep -q installed; }; then

ufw allow in on lo
ufw allow out on lo
ufw deny in from 127.0.0.0/8
ufw deny in from ::1

else
    >&2 echo 'Remediation is not applicable, nothing was done'
fi

Warning

Changing firewall settings while connected over network can result in being locked out of the system.