ConfigServer Firewall (csf) is a Stateful Packet Inspection (SPI)

It is a firewall that keeps track of the state of network connections (such as TCP streams, UDP communication) travelling across it. The firewall is programmed to distinguish legitimate packets for different types of connections. Only packets matching a known connection state will be allowed by the firewall; others will be rejected.

It used iptables firewall which is simple, straight-forward, easy and flexible to configure and secure with more checks to ensure smooth operation.

Installation

If APF and BFD is already enabled, then you have to disable it. Otherwise both (CSF and APF) will conflict.

To disable APF,

CSF is configured to work on a cPanel server with all the standard cPanel ports open.

The configuration file is located at /etc/csf directory.