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A brief look at Cookie Clobbering
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Author:  flying_circus [ Sun Aug 14, 2011 11:59 pm ]
Post subject:  A brief look at Cookie Clobbering

I’ve been doing a fair amount of research lately and I came across an idea that I found particularly interesting, especially after some recommendations I made in passing a token in a secure cookie in this thread: ... 9&p=657645

As the story goes, if a cookie is set on an https request with the secure flag set to TRUE, you can then overwrite the secure cookie on a sub-sequent non-secure request. This seems odd behavior due to the same-origin-policy.
I have included a quick snippet of code as an example. It requires you to have access to a server with SSL.

This behavior was observed in:
- Windows 7 \ Internet Explorer 8
- Windows 7 \ Firefox 5.0
- Windows 7 \ 13.0.782.112 m

Syntax: [ Download ] [ Hide ]
  # Definitions
   define('COOKIE_NAME', 'MySecureCookie');
  # Variables
   $payload = isset($_COOKIE[COOKIE_NAME]) ? $_COOKIE[COOKIE_NAME] : htmlentities('(Cookie Not Sent By Client)');
    $action = isset($_POST['action']) ? $_POST['action'] : '';
  # Functions
   function is_https()
      if(  (isset($_SERVER['HTTPS']) && mb_strtolower($_SERVER['HTTPS']) == "on")
        || (isset($_SERVER['HTTPS']) && $_SERVER['HTTPS'] == 1)
        || (isset($_SERVER['SERVER_PORT']) && $_SERVER["SERVER_PORT"] == 443)
        return true;
      return false;
    function is_postback()
     return (isset($_SERVER['REQUEST_METHOD']) && mb_strtolower($_SERVER['REQUEST_METHOD']) == "post");
  # Action
   if(is_postback()) {
      if($action == 'set_cookie') {
        if(is_https()) {
          setcookie (COOKIE_NAME, 'HTTPS_TOKEN: 123456', 0, '/', '', TRUE);
        } else {
          setcookie (COOKIE_NAME, 'HTTP_OVERWRITE', 0, '/', '', TRUE);
        header('location: index.php');
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN" "">
<html xmlns="">
    <title>Security: Cookie Clobbering</title>
    <meta http-equiv="Content-Type" content="text/html; charset=UTF-8" />
      <h1>Example: Cookie Clobbering</h1>
      <p>As per the design of my user login system, when a user logs in, they must do so over a secure connection (HTTPS).  Upon successful authentication, the user is assigned a secure token which is stored in a cookie (a cookie with the secure flag set to TRUE).  This tells the browser to send the cookie payload over a secure connection only.</p>
      <p>The suspicion is that you can overwrite the secure (HTTPS) cookie from a non-secure (HTTP) request.</p>
      <hr />
      <strong>Current Connection Protocol: <?php print is_https() ? 'HTTPS' : 'HTTP'; ?></strong>
      <br />
      <strong>Current Value of "$_COOKIE['<?php print COOKIE_NAME; ?>']": <?php print $payload; ?></strong>
      <hr />
      <form action="<?php print is_https() ? "http://{$_SERVER['SERVER_NAME']}{$_SERVER['REQUEST_URI']}" : "https://{$_SERVER['SERVER_NAME']}{$_SERVER['REQUEST_URI']}"; ?>" method="post">
        <input type="hidden" name="action" value="change_protocol">
        <input type="submit" value="Change Protocol">
      <form action="index.php" method="post">
        <input type="hidden" name="action" value="set_cookie">
        <input type="submit" name="cookie_value" value="Set Cookie Value and Refresh Page">

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