Symptoms

Login to PHP application using POST request fails without any error messages.

ModSecurity is installed and set into 'Tradeoff' or 'Thorough' mode in Tools & Settings > Web Application Firewall > Settings .

Causes

ModSecurity's analysis of POST data breaks login mechanism of application.

Resolution

Switch ModSecurity mode to 'Fast' in Tools & Settings > Web Application Firewall > Settings .

For Windows Server, please correct modsecurity.conf file in `C:\Program Files\ModSecurity IIS`, set:

SecRequestBodyAccess Off

and restart IIS.