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How to install the ModSecurity NGINX module in CentOS/RHEL 8

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NGINX is an open-source web server well known for its high performance and the vast array of features available through modules.

ModSecurity is an open-source web application firewall. It is available as a library and can be added to NGINX using a connector module.

Follow these instructions to easily install the RPM package of the ModSecurity module for NGINX.

Install nginx-module-security in CentOS/RHEL 8

The ModSecurity module is compatible with the latest stable and mainline NGINX versions.

Step 1. Set up GetPageSpeed RPM respotiroy

sudo dnf -y install https://extras.getpagespeed.com/release-latest.rpm

Step 2. Install NGINX

If you already have NGINX set up, you can skip this step.

Otherwise, run the following command to install NGINX:

sudo dnf -y install nginx 

Step 3. Install ModSecurity NGINX module

Install ModSecurity module itself:

sudo dnf -y install nginx-module-security

Follow the installation prompt to import GPG public key that is used for verifying packages.

The libmodsecurity library dependency will be installed for you.

Step 4. Enable the module

Next, enable your NGINX to load the ModSecurity dynamic module by editing the NGINX configuration. Simply follow the installer’s suggestion:

----------------------------------------------------------------------

The security dynamic module for nginx has been installed.
To enable this module, add the following to /etc/nginx/nginx.conf
and reload nginx:

    load_module modules/ngx_http_modsecurity_module.so;

Please refer to the module documentation for further details:
https://github.com/SpiderLabs/ModSecurity-nginx

----------------------------------------------------------------------

Install OWASP CRS

ModSecurity needs some detection rules to work with.
A popular ruleset for ModSecurity is OWASP ModSecurity Core Rule Set (CRS).

You can set up OWASP Core Rule Set now with:

sudo dnf -y install nginx-owasp-crs

Enable OWASP CRS

To enable the installed rule set (and thus put ModSecurity to action), you can add the following to a site configuration:

server {
    modsecurity on;
    location / {
        modsecurity_rules_file /etc/nginx/modsec_includes.conf;
    }
}

Verify

Now you have it installed and configured. How to see it is actually protecting your website?

Navigate to a URL like this: http://example.com/?q=%22%3E%3Cscript%3Ealert(1)%3C/script%3E%27

It should trigger a 403 Forbidden error, similar to the screenshot below:

NGINX ModSecurity Protection
NGINX ModSecurity Protection

Monitor False Positives

As with all-things-ModSecurity, you should tune things specifically for your web app. Monitor the main log file /var/log/nginx/modsec_audit.log for false positives. You can see details of each denied request in /var/log/nginx/modsec directory.

SELinux compatibility

The package is fully compatible with SELinux.

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