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Lack of data validation - HTML code

Need​

Implementation of proper data validation for HTML code

Context​

  • Usage of Java 8 for developing applications with enhanced features and performance
  • Usage of javax.servlet-api for building Java web applications with Servlets

Description​

Non compliant code​

import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;

public class DataServlet extends HttpServlet {
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        String userContent = request.getParameter("userContent");
        response.setContentType("application/json");
        response.getWriter().write("{\\"message\\": \\"" + userContent + "\\"}");
    }
}

The above code represents a Servlet that accepts POST requests. The doPost method retrieves the parameter userContent from the request and directly embeds it into a JSON response without any form of validation or sanitization.

The vulnerability lies in the fact that the userContent parameter is directly embedded into the JSON response. This means that an attacker could potentially inject valid HTML code as the userContent parameter. When this JSON response is interpreted by a website, the injected HTML code would be executed.

For example, an attacker could send a POST request with the userContent parameter as <script>alert('XSS Attack');</script>. This would result in the following JSON response:

{
  "message": "<script>alert('XSS Attack');</script>"
}

When this JSON response is interpreted by a website, the JavaScript code within the <script> tags would be executed, causing an alert box with the message 'XSS Attack' to appear. This is a simple example, but the JavaScript code could be used to perform more malicious actions, such as stealing sensitive information.

This vulnerability could be exploited to conduct Cross-Site Scripting (XSS) attacks, which could lead to a variety of security issues such as session hijacking, identity theft, defacement of the website, and other malicious activities.

Steps​

  • Implement input validation to ensure that the user input is safe and does not contain any malicious HTML code.
  • Use appropriate HTML encoding or escaping techniques to sanitize the user input before displaying it on the website.
  • Consider using a library or framework that provides built-in protection against HTML injection attacks.
  • Regularly update and patch the software to ensure that any known vulnerabilities are fixed.
  • Educate developers about secure coding practices and the risks associated with lack of data validation.

Compliant code​

import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;
import org.owasp.encoder.Encode;

public class DataServlet extends HttpServlet {
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        String userContent = request.getParameter("userContent");
        String safeUserContent = Encode.forHtml(userContent);
        response.setContentType("application/json");
        response.getWriter().write("{\\"message\\": \\"" + safeUserContent + "\\"}");
    }
}

The original code was vulnerable to HTML injection attacks because it did not validate or sanitize user input before using it. This could allow an attacker to inject malicious HTML code, which would then be interpreted by the website that receives the JSON response.

The fixed code uses the OWASP Java Encoder library to sanitize the user input. The Encode.forHtml(userContent) method encodes the user input for use in HTML, effectively preventing HTML injection attacks. This method replaces any potentially dangerous characters with their HTML-encoded equivalents. For example, the less-than character ("<") would be replaced with "<".

This fix ensures that the user input is safe and does not contain any malicious HTML code. It is a good practice to always validate and sanitize user input, especially when it is used in a context that could make the application vulnerable to injection attacks.

In addition to this fix, it is recommended to use a library or framework that provides built-in protection against HTML injection attacks, to regularly update and patch the software to fix any known vulnerabilities, and to educate developers about secure coding practices and the risks associated with lack of data validation.

References​

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