Exploit the challenge the other way, and get a remote shell :
https://pwn-maher.blogspot.com/2020/07/pwn4-csivit-2020-pwn-intended-get-shell.html

Original writeup (https://pwn-maher.blogspot.com/2020/07/pwn4-csivit-2020-pwn-intended-get-shell.html).