Firewalls protect networks by filtering traffic and dropping bad or unwanted network packets. While firewalls are available for many years, their configuration is usually cluttered up and allowing too much traffic.
Regular audits are needed to make sure the firewall configuration is properly adjusted to the IT environment and business requirements.
By looking on the inside of systems, Lynis can determine the required network flows and compare the firewall configuration.
A service is listed in the firewall configuration, yet no service is running on the related system. It will be flagged as a possible improvement.