Among Us CTF Web Hard 900
From the source code we know that the flag is stored in flag.txt. We're able to upload images which are then visible on the site. By reading the source code you can notice that their is no path validations on the exec url. We are then able to craft a python script that reads the flag file and prints it to stdio. We can then call the script by visiting isss.io:5000/exec/imgs/flag.png.