[https://infosec.rm-it.de/2018/04/15/wpictf-2018-shell-jail-1/](https://infosec.rm-it.de/2018/04/15/wpictf-2018-shell-jail-1/)

Original writeup (https://infosec.rm-it.de/2018/04/15/wpictf-2018-shell-jail-1/).