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security - preventing csrf in php

  1. Requiring authentication in GET and POST parameters, not only cookies;

  2. Checking the HTTP Referer header;

saw this post on wikipedia and was wondering how I can apply them

ok...I am using the Kohana PHP framework and I have the facility to determine the referrer header, but what exactly do I check in the referrer header? the framework function only returns the URL of the referrer

and how do I validate GET and POST params? against what? stored information? expected type?

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To prevent CSRF you'll want to validate a one-time token, POST'ed and associated with the current session. Something like the following . . .

On the page where the user requests to delete a record:

confirm.php

<?php
 session_start();
 $token = isset($_SESSION['delete_customer_token']) ? $_SESSION['delete_customer_token'] : "";
 if (!$token) {
     // generate token and persist for later verification
     // - in practice use openssl_random_pseudo_bytes() or similar instead of uniqid() 
     $token = md5(uniqid());
     $_SESSION['delete_customer_token']= $token;
 }
 session_write_close();
?>
<html>
<body>
<form method="post" action="confirm_save.php">
 <input type="hidden" name="token" value="<?php echo $token; ?>" />
Do you really want to delete?
<input type="submit" value=" Yes " />
<input type="button" value=" No " onclick="history.go(-1);" />
</form>
</body>
</html>

Then when it comes to actually deleting the record:

confirm_save.php

<?php
 session_start();
 // validate token
 $token = isset($_SESSION['delete_customer_token']) ? $_SESSION['delete_customer_token'] : "";
 if ($token && $_POST['token'] === $token) {
   // delete the record
   ...
   // remove token after successful delete
   unset($_SESSION['delete_customer_token']);
 } else {
   // log potential CSRF attack.
 }
 session_write_close();
?>

The token should be hard to guess, unique for each delete request, accepted via $_POST only and expire after a few minutes (expiration not shown in this example).


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