## Exploit

1. In the survey page choosing a grade will send a POST request. The client-side form allows values between 1 and 10.
1. Sending a request with a value outside the range (`curl --data valeur=42 --data sujet=2 "http://10.0.2.15/?page=survey" | grep flag`) will give you a flag.

## Fix

Client-side data should not be trusted and should be verified and sanitized both client-side and server-side.