Natas 6

After loading the page, we see

By checking the source code which shows

We see some interesting php code which shows to include the secret at includes/secret.inc

<?

include "includes/secret.inc";

    if(array_key_exists("submit", $_POST)) {
        if($secret == $_POST['secret']) {
        print "Access granted. The password for natas7 is <censored>";
    } else {
        print "Wrong secret";
    }
    }
?>

By accessing http://natas6.natas.labs.overthewire.org/includes/secret.inc, it shows

<?
$secret = "FOEIUWGHFEEUHOFUOIU";
?>

By simply submitting this,

And thus the password is bmg8SvU1LizuWjx3y7xkNERkHxGre0GS