Execution After Redirect (EAR)

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Author: Robert Gilbert (amroot)

Overview

Execution After Redirect (EAR) is an attack where an attacker ignores redirects and retrieves sensitive content intended for authenticated users. A successful EAR exploit can lead to complete compromise of the application.

How to Test for EAR Vulnerabilities

Using most proxies it is possible to ignore redirects and display what is returned. In this test we use Burp Proxy. Intercept request https://vulnerablehost.com/managment_console

  1. Send to repeater.
  2. View response.

How to Prevent EAR Vulnerabilities

Proper termination should be performed after redirects. In a function a return should be performed. In other instances functions such as die() should be performed. This will tell the application to terminate regardless of if the page is redirected or not.

Examples

The following code will check to see if the parameter “loggedin” is true. If it is not true, it uses JavaScript to redirect the user to the login page. Using the “How to Test for EAR Vulnerabilities” section or by disabling JavaScript in the browser, the same request is repeated without following the JavaScript redirect and the “Admin” section is accessible without authentication.

<?php if (!$loggedin) {
     print "<script>window.location = '/login';</script>\n\n"; 
} ?>
<h1>Admin</h1>
<a href=/mu>Manage Users</a><br />
<a href=/ud>Update Database Settings</a>

References

Watch Star