ModSecurity is an open source, cross-platform web application firewall (WAF) module. Known as the "Swiss Army Knife" of WAFs, it enables web application defenders to gain visibility into HTTP(S) traffic and provides a power rules language and API to implement advanced protections.
A list of the most important usage scenarios:
-Real-time application security monitoring and access control -Virtual patching -Full HTTP traffic logging -Continuous passive security assessment -Web application hardening