This tutorial is going to show you how to install and use ModSecurity with Apache on Debian/Ubuntu servers. ModSecurity is the most well-known open-source web application firewall (WAF), providing comprehensive protection for your web applications (like WordPress, Nextcloud, Ghost etc) against a wide range of Layer 7 (HTTP) attacks, such as SQL injection, cross-site scripting, and local file inclusion.

https://www.linuxbabe.com/security/modsecurity-apache-debian-ubuntu