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Lack of data validation - Web Service

Need​

Implementation of robust data validation and input sanitization mechanisms

Context​

  • Usage of Java for building cross-platform applications
  • Usage of javax.servlet for Java web development with Servlets
  • Usage of java.io for input and output operations in Java programming

Description​

Non compliant code​

import javax.servlet.*;
import javax.servlet.http.*;
import java.io.*;

public class VulnerableServlet extends HttpServlet {
    public void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        String username = request.getParameter("username");
        String password = request.getParameter("password");
        
        // Process the username and password
    }
}

The code above represents a servlet in a Java web application that handles HTTP POST requests. The servlet retrieves the username and password parameters from the incoming request without performing any form of validation on these inputs.

The username and password are retrieved directly from the HTTP request with the request.getParameter() method. This method returns the value of a request parameter as a String, or null if the parameter does not exist. The problem here is that the servlet does not validate these parameters in any way before processing them.

This lack of validation means that an attacker could potentially send malicious input in these fields. For example, they might send SQL commands in an attempt to perform an SQL Injection attack or send a very large amount of data to cause a Buffer Overflow attack.

The servlet also does not have any restrictions on the size of the fields that can be sent to the server. This means that an attacker could potentially send a very large amount of data in these fields, which could lead to a Denial of Service (DoS) attack if the server becomes overwhelmed with processing this data.

In summary, this servlet is vulnerable to several types of attacks due to its lack of data validation.

Steps​

  • Implement server-side data validation to ensure that only valid and expected data is accepted.
  • Validate the data received in the 'username' and 'password' parameters to prevent the use of special characters or any other potentially harmful input.
  • Implement input sanitization techniques such as removing or escaping special characters to prevent injection attacks.
  • Implement size validation to ensure that the length of the input does not exceed the expected limit.
  • Consider using a secure password storage mechanism, such as hashing and salting, to protect user passwords.
  • Implement proper error handling and logging to detect and respond to any potential attacks or abnormal behavior.
  • Regularly update and patch the server-side code to address any newly discovered vulnerabilities.

Compliant code​

import javax.servlet.*;
import javax.servlet.http.*;
import java.io.*;
import java.util.regex.*;

public class SecureServlet extends HttpServlet {
    private static final int MAX_LENGTH = 20;
    private static final String REGEX = "^[a-zA-Z0-9]*$";

    public void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        String username = request.getParameter("username");
        String password = request.getParameter("password");

        if (!isValid(username) || !isValid(password)) {
            response.sendError(HttpServletResponse.SC_BAD_REQUEST, "Invalid input");
            return;
        }

        // Process the username and password
    }

    private boolean isValid(String input) {
        if (input == null || input.length() > MAX_LENGTH) {
            return false;
        }

        Pattern pattern = Pattern.compile(REGEX);
        Matcher matcher = pattern.matcher(input);

        return matcher.matches();
    }
}

The updated code now includes server-side data validation for the 'username' and 'password' parameters. This is done in the isValid method, which checks if the input is null, if it exceeds the maximum length, and if it matches the regular expression that only allows alphanumeric characters.

The doPost method now checks if the 'username' and 'password' parameters are valid before processing them. If they are not valid, it sends a 400 Bad Request error to the client.

The MAX_LENGTH constant is used to limit the length of the input to prevent buffer overflow attacks. The REGEX constant is a regular expression that only matches alphanumeric characters, preventing the use of special characters that could lead to injection attacks.

This code does not include a secure password storage mechanism, error handling, logging, or server-side code updates and patches. These should be implemented as part of a comprehensive security strategy.

References​

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