Unable to access .CGI on embedded webserver

Good Day. I’m currently developing an embedded device using mongoose as the webserver. My goal is to parse the data from an HTML file and process the data using CGI. However, I am encountering an issue when accessing .CGI / .PHP files. Browser returns with 500 Server Error : Permission Denied.

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But when I’m accessing common files such as .HTML, Javascript, XML, it successfully loads the file. What might be the cause of this error? Thank you in advance