It's waiting, the "tty" command which is invoked a "a.out" causes the tty to receive the sequence of characters specified -- in this case "id\n". The vulnerabi

It's waiting, the "tty" command which is invoked a "a.out" causes the tty to receive the sequence of characters specified -- in this case "id\n". The vulnerability here is that if, as one user, you switch user contexts and then later (10 seconds, in this case, hence "sleep 10") the command interacts with the tty over the file descriptor that had been given to the child process and not killed when you exited the shell that spawned it.