in this challenge we use command injection, this is the vuln part: passthru("grep -i $key dictionary.txt");

here we can’t use ;, so we will use this payload we gives a /etc/natas_webpass/natas11 if you don’t get the password for ‘a’, try insert different characters.

Flag: UJdqkK1pTu6VLt9UHWAgRZz6sVUZ3lEk