Information
Configure the loopback interface to accept traffic. Configure all other interfaces to deny traffic to the loopback network (127.0.0.0/8 for IPv4 and ::1/128 for IPv6).
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 (127.0.0.0/8 for IPv4 and ::1/128 for IPv6) traffic should be seen, all other interfaces should ignore traffic on this network as an anti-spoofing measure.
Solution
Run the following commands to implement the loopback rules:
# ufw allow in on lo
# ufw allow out from lo
# sudo ufw deny in from 127.0.0.0/8
# sudo ufw deny in from ::1