2
\$\begingroup\$

I wish to redirect users to the login page if they attempt to visit a page which requires them to be logged in. After logging in, however, I want to redirect the user back to their original destination. I've written a "redirect.php" script which is to be included on all such pages:

<?php
require "session.php";
if(!$user){
    header("Location: login.php?dest=".urlencode($_SERVER["REQUEST_URI"]));
    die();
}
?>

Then on my login page I have the following:

<?php 
$dest = "./";
if(isset($_GET["dest"])){
    $dest = $_GET["dest"];
}
?>

with the following JavaScript:

var URL = "<?php echo $dest; ?>";
//...
//upon successful login (via AJAX):
window.location.replace(URL);

Everything here works as intended but where does this stand from a security standpoint?

One vulnerability that comes to mind is something like

http://mysite.com/login.php?dest=http://phishingsite.com

How might I best prevent something like this? Would regex be suitable here?

Are there any other security concerns with this type of thing? Perhaps a standard way of doing this? Or better yet, a method which does not use GET variables at all?

\$\endgroup\$
5
  • \$\begingroup\$ Anything speaking against using a session for this rather than an URL parameter? \$\endgroup\$
    – Mario
    Dec 18, 2014 at 15:09
  • \$\begingroup\$ No, not at all. I hadn't even considered the use of sessions prior to the user actually logging in. Care to expand? I see this approach requiring an additional page request unless maybe dedicating another page to the redirection... \$\endgroup\$
    – Abovestand
    Dec 18, 2014 at 15:32
  • \$\begingroup\$ I would consider using sessions as @Mario pointed out. Additionally, to stop against phishing, you could check that the domain is correct before redirecting \$\endgroup\$ Dec 18, 2014 at 15:43
  • \$\begingroup\$ Are there any downsides to using sessions? Because I'm having a hard time coming up with any reasons to stick with GET besides the fact that I've seen them used before. \$\endgroup\$
    – Abovestand
    Dec 18, 2014 at 15:52
  • \$\begingroup\$ The one main advantage is you can send the redirect url to anyone, I do this quite often when telling clients where to go once logging in to their CMS - so it redirects them directly to the page they need to be on - see my answer \$\endgroup\$ Dec 18, 2014 at 15:55

1 Answer 1

5
\$\begingroup\$

The way you're doing it has advantages over a session based redirect because you have the ability to link people directly to that login with redirect URL.

The disadvantage is phishing as you pointed out.

http://www.mysite.com/login.php?dest=http://mysite.phishing.com/

The way you're doing this, using $_SERVER['REQUEST_URI'] means you expect the $_GET['dest'] to only include a path, not a domain.

So you could add a check in the login page where it sets the $dest

$dest = "./";
if(isset($_GET["dest"]))
{
    $parts = parse_url( $_GET['dest'] );

    // if there is no `host` key set in the parse_url array, then its an internal path
    // so set the new $dest
    if( !isset( $parts['host'] ) )
    {
        $dest = $_GET["dest"];
    }
}
\$\endgroup\$

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge that you have read and understand our privacy policy and code of conduct.

Not the answer you're looking for? Browse other questions tagged or ask your own question.