zerkms

<?php

session_start();

$token = calculate_token();

$session_token = isset($_SESSION['token']) ? $_SESSION['token'] : null;

if (!$session_token) {
    $_SESSION['token'] = $token;
} elseif ($session_token != $token) {
    session_regenerate_id();
    $_SESSION = array();
    $_SESSION['token'] = $token;
}

function calculate_token()
{
    $ip = !empty($_SERVER['REMOTE_ADDR']) ? $_SERVER['REMOTE_ADDR'] : '127.0.0.1';
    $ua = !empty($_SERVER['HTTP_USER_AGENT']) ? $_SERVER['HTTP_USER_AGENT'] : 'no ua';
    $charset = !empty($_SERVER['HTTP_ACCEPT_CHARSET']) ? $_SERVER['HTTP_ACCEPT_CHARSET'] : 'no charset';
    $ip = substr($ip, 0, strrpos($ip, '.') - 1);
    return md5($ua . $ip . $charset);
}

if (isset($_POST['token'])) {
    if ($_POST['token'] != $token) {
        echo 'FU';
        exit;
    }

    if (isset($_POST['url'])) {
        header('Location: ' . $_POST['url']);
        exit;
    }

    echo 'There was no url';
}

?>

<form method="POST">
<input type="input" name="foo" />
<input type="hidden" name="url" value="http://google.com" />
<input type="hidden" name="token" value="<?php echo $token; ?>" />
<input type="submit" />
</form>