In my Slim PHP application container, the only way I could reproduce the PHP2SHELL behavior was by adding `index.php` and `upload.php` from the attached gist to the webroot.

As others have said, there are probably other ways to reproduce it, but it requires a lot of prior knowledge of the app environment, or at least a good guess.

https://gist.github.com/mashiox/462e15b45a4c891b3a843e11b1d2...