Unable to activate ModSecurity

Note: please note that Liferay has renamed its Liferay Experience Could offerings to Liferay SaaS (formerly LXC) and Liferay PaaS (formerly LXC-SM).

Issue

When trying to activate ModSecurity or add new rules following the official documentation, it doesn't work.
The debug log is turned on but it doesn't print anything.

Environment

Liferay PaaS

Resolution

First of all, double check that you have properly configured LCP_WEBSERVER_MODSECURITY environment variable in webserver/LCP.json.
Apart from the audit log (/var/log/modsec_audit.log), try to turn on the debug log in modsecurity.conf:
```
SecDebugLog /var/log/modsec_debug.log
SecDebugLogLevel 9
```

If, despite that, nothing is printed in modsec_audit.log or modsec_debug.log that helps you troubleshoot the issue, you may see something like this in Nginx logs:

2023/12/04 18:31:53 [emerg] 83#83: "modsecurity_rules_file" directive Rules error. File: /etc/nginx/modsec/modsecurity.conf. Line: 194. Column: 16. Failed to start DebugLog: Failed to open file: /opt/modsecurity/var/log/debug.log in /etc/nginx/nginx.conf:62
nginx: [emerg] "modsecurity_rules_file" directive Rules error. File: /etc/nginx/modsec/modsecurity.conf. Line: 194. Column: 16. Failed to start DebugLog: Failed to open file: /opt/modsecurity/var/log/debug.log in /etc/nginx/nginx.conf:62

Even if this is not your case, double check your own nginx.conf. You may have some directives that conflict with your ModSecurity configuration, such as modsecurity off;.

Additional Information

Liferay Learn: Web Application Firewall
Nginx: ModSecurity: Logging and Debugging