Skip to main content

Lack of data validation - Input Length

Need​

Implementation of input length validation to prevent excessive data submission

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 VulnerableServlet extends javax.servlet.http.HttpServlet {

    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        String content = request.getParameter("content");
        processContent(content);
    }

    private void processContent(String content) {
        // Some processing logic here
    }
}

The above code is a simple servlet that accepts POST requests. The doPost method retrieves a parameter "content" from the request without checking its length. This parameter is then passed to the processContent method for further processing.

The vulnerability lies in the lack of input length validation. An attacker could potentially send a POST request with an exceptionally long value for the "content" parameter. This could lead to several issues such as:

  • Buffer overflow: If the server tries to store the content in a buffer that isn't large enough, it could overflow, leading to erratic program behavior or even a system crash.

  • Denial of Service (DoS): If the server tries to process an extremely large amount of data, it could consume significant system resources (CPU, memory), slowing down the system or even causing it to become unresponsive.

  • Injection attacks: If the content is used in a context where its length isn't properly handled (e.g., in a SQL query or a command line argument), it could potentially lead to injection attacks.

In this case, the lack of input length validation creates a security vulnerability that could be exploited by an attacker to cause harm to the system.

Steps​

  • Implement input validation to check the length of the 'content' parameter.
  • Define a maximum allowed length for the 'content' parameter and reject requests that exceed this limit.
  • Consider using a whitelist approach to validate the content, allowing only specific characters or patterns.
  • Sanitize the input by removing any potentially harmful characters or sequences.
  • Implement rate limiting or throttling mechanisms to prevent abuse of the endpoint.
  • Consider implementing a content size limit for the entire request body, not just the 'content' parameter.

Compliant code​

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

public class SecureServlet extends javax.servlet.http.HttpServlet {
    private static final int MAX_CONTENT_LENGTH = 500; // Define your maximum content length

    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        String content = request.getParameter("content");
        if (content != null && content.length() > MAX_CONTENT_LENGTH) {
            response.sendError(HttpServletResponse.SC_BAD_REQUEST, "Content length exceeded");
            return;
        }
        processContent(content);
    }

    private void processContent(String content) {
        // Some processing logic here
    }
}

The above code fixes the vulnerability by implementing input validation to check the length of the 'content' parameter.

A constant MAX_CONTENT_LENGTH is defined to specify the maximum allowed length for the 'content' parameter. In the doPost method, before processing the content, we check if the length of the content exceeds this maximum limit. If it does, we send an error response with the status code SC_BAD_REQUEST (400) and a message indicating that the content length has been exceeded. This effectively rejects requests that try to send content larger than the allowed limit.

This approach helps to prevent potential attacks that involve sending massive amounts of characters to the endpoint, thus reducing the attack vectors.

Please note that this is a basic fix and there are other security measures that could be implemented for more robust protection. For example, you could also consider using a whitelist approach to validate the content, allowing only specific characters or patterns. You could sanitize the input by removing any potentially harmful characters or sequences. Implementing rate limiting or throttling mechanisms can help to prevent abuse of the endpoint. Additionally, you could consider implementing a content size limit for the entire request body, not just the 'content' parameter.

References​

Last updated on