How can I misinform my inclusion statements?

Question

How to clear this so that users cannot pull pages outside the local domain?

<?php
 if(!empty($_GET['page']))
 {
  include($_GET['page']);
 }
 else
 {
  include('home.php');
 }
?>

Answer 1

The safest way is to list the white pages:

$page = 'home.php';

$allowedPages = array('one.php', 'two.php', ...);

if (!empty($_GET['page']) && in_array($_GET['page'], $allowedPages))
    $page = $_GET['page'];

include $page;

Answer 2

// get the absolute file name of the page we want to see
$ page = realpath ($ _ GET ['page']);

// get the directory in which pages are
$ mydir = dirname (__ FILE__);

// see if the included page is inside this allowed dir
if ($ page === false || substr ($ page, 0, strlen ($ mydir)! = $ mydir) {
 die ('go away hacker');
} else {
 include $ page;
}

Answer 3

This is not verified. I just wrote it very quickly, but it should work (I hope), and it will definitely give you the foundation to start with.

define('DEFAULT_PAGE', 'home.php');
define('ALLOWED_PAGES_EXPRESSION', '^[\/]+\.php$|^[\/]+\.html$');

function ValidateRequestedPage($p)
{
    $errors_found = False;

        // Make sure this isn't someone trying to reference directories absolutely.
    if (preg_match('^\/.+$', $p))
    {
        $errors_found = True;
    }

        // Disable access to hidden files (IE, .htaccess), and parent directory.
    if (preg_match('^\..+$', $p))
    {
        $errors_found = True;
    }


        // This shouldn't be needed for secure servers, but test for remote includes just in case...
    if (preg_match('.+\:\/\/.+', $p))
    {
        $errors_found = True;
    }

    if (!preg_match(ALLOWED_PAGES_EXPRESSION, $p))
    {
        $errors_found = True;
    }

    return !$errors_found;
}

if (!isset($_GET['page'])) { $page = DEFAULT_PAGE; }
else { $page = $_GET['page']; }

if ( !ValidateRequestedPage($page) )
{
    /* This is called when an error has occured on the page check. You probably
       want to show a 404 here instead of returning False. */
    return False;
}

// This suggests that a valid page is being used.
require_once($page);

Answer 4

Just use the switch statement.

Check if the $ _GET var parameter is set, and then run it in cases and by default go to home.php