[https://www.alevsk.com/2019/01/fireshell-ctf-2019-bad-injections-web/](https://www.alevsk.com/2019/01/fireshell-ctf-2019-bad-injections-web/)

Original writeup (https://www.alevsk.com/2019/01/fireshell-ctf-2019-bad-injections-web/).