CSF Firewall

ConfigServer Security and Firewall (CSF) is a free, advanced firewall configuration script and login/intrusion detection suite for Linux servers. It is one of the most widely deployed security tools in the shared hosting industry, particularly on cPanel servers.

CSF provides a comprehensive iptables/nftables firewall with an easy-to-use configuration interface. It includes Login Failure Daemon (LFD) that monitors log files for failed authentication attempts and automatically blocks offending IP addresses. This covers SSH, FTP, SMTP, POP3, IMAP, cPanel, WHM, and many other services.

Key features include SYN flood protection, port scan detection, suspicious process tracking, excessive connection blocking, IP blocklist integration (Spamhaus, DShield, etc.), and country-based access control. The UI plugin for cPanel/WHM/DirectAdmin provides a graphical interface for managing firewall rules, viewing blocked IPs, and checking the security status of the server.

CSF also includes a Server Security Check feature that audits the server configuration and flags potential security issues. It checks file permissions, open ports, Apache/PHP settings, and other common misconfiguration vectors.

Despite being free, CSF is remarkably full-featured and well-maintained. It is often the first security tool installed on a new cPanel server and many managed hosting providers include it as part of their standard server stack.