Bit Form < 1.9 - RCE via Unauthenticated Arbitrary File Upload

The plugin does not validate the file types uploaded via it’s file upload form field, allowing unauthenticated users to upload arbitrary files types such as PHP or HTML files to the server, leading to Remote Code Execution.

PoC

As an unauthenticated user access a form containing a File Upload form. Upload a malicious html file (containing a malicious js for example) named after an image file, for example, and intercept the request. Change the filename’s extension in the request to html and forward the request. The malicious HTML will be available on the uploads directory.