App - Script

I’m very new to CTFs and I’m stuck on this first challenge.

I understand what you have to do but something doesn’t click for me.
Since ch11 has setuid, it runs every command as "app-script-ch11-cracked" so it has read permissions on .passwd.

[Th1b4ud : spoil ! Keep trying you are on the right way]

What am I missing here ? Do I need to compile the C file ?

I read the related ressources, I’ve also tried modifying permissions but I can’t chmod my files to desired user.

[Th1b4ud : why did you put solution leak ?]

[Th1b4ud : no ads thanks]