public void doGet(HttpServletRequest request, HttpServletResponse response) {

String username = request.getParameter("username");

if (validator.isValidInput("HTTP parameter", username, "username", 20, false)) {

// GOOD: The input is sanitized before being written to the response.

request.getSession().setAttribute("username", username);

}

}

In order to maintain a trust boundary, data from less trusted sources should be validated before being used.

<p>

In the first (bad) example, the server accepts a parameter from the user and uses it to set the username without validation.

</p>

<sample src="examples/TrustBoundaryVulnerable.java" />

<p>

In the second (good) example, the server validates the parameter before using it to set the username.

</p>

<sample src="examples/TrustBoundaryFixed.java" />

public void doGet(HttpServletRequest request, HttpServletResponse response) {

String username = request.getParameter("username");

// BAD: The input is written to the response without being sanitized.

request.getSession().setAttribute("username", username);

}