Need

Implementation of robust data validation for numbers

Context

• Usage of Java for building robust and scalable applications
• Usage of javax.servlet for building Java web applications
• Usage of javax.servlet.http for handling HTTP requests and responses in Java Servlet development

Description

Non compliant code

        import javax.servlet.*;
import javax.servlet.http.*;

public class DataValidationServlet extends HttpServlet {

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

        // Process the number without validating
        int processedNumber = processNumber(number);
        
        // Rest of the code
    }

    private int processNumber(String number) {
        // Assume this function does some complex processing with the number
        return Integer.parseInt(number);
    }
}
        
        

The above code snippet is a simple example of a Servlet that processes a number received from a HTTP POST request. The number is retrieved from the request parameters and is passed to a processNumber function without any validation.

The vulnerability lies in the lack of data validation of the input number. The processNumber function assumes that the input is always a valid integer and directly parses it using Integer.parseInt.

If an attacker sends a request with a non-numeric value for the number parameter, it will cause a NumberFormatException to be thrown, leading to an error response to the user and potentially breaking the business logic.

Moreover, if the processNumber function involves more complex operations that are sensitive to the input values, it can lead to further unexpected behaviors or even security risks. For example, if the function is used to calculate the price based on the number, an attacker might be able to manipulate the price by providing a negative number.

In conclusion, this code is vulnerable due to the lack of data validation for the input number. It assumes that the input is always valid and does not handle the case where it is not. This can lead to unexpected behaviors and potential security risks.

Steps

• Implement data validation to ensure that the input number is valid
• Use appropriate validation techniques such as range checks, type checks, and input sanitization
• Validate the input number against the expected format or range of values
• Handle invalid input gracefully by providing appropriate error messages or fallback values
• Consider using a validation library or framework to simplify the validation process
• Regularly update and maintain the validation logic to adapt to changing requirements or security threats

Compliant code

        import javax.servlet.*;
import javax.servlet.http.*;

public class DataValidationServlet extends HttpServlet {

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

        // Validate the number before processing
        if (!isValidNumber(number)) {
            response.sendError(HttpServletResponse.SC_BAD_REQUEST, "Invalid number format");
            return;
        }

        int processedNumber = processNumber(number);
        
        // Rest of the code
    }

    private int processNumber(String number) {
        // Assume this function does some complex processing with the number
        return Integer.parseInt(number);
    }

    private boolean isValidNumber(String number) {
        // Check if the number is not null, is a number and within the valid range
        if (number == null) {
            return false;
        }
        try {
            int num = Integer.parseInt(number);
            // Check if the number is within the valid range
            if (num < 0 || num > 100) {
                return false;
            }
        } catch (NumberFormatException e) {
            return false;
        }
        return true;
    }
}
        
        

The updated code includes a new method isValidNumber(String number) which validates the input number. This method checks if the input is not null, if it is a valid integer, and if it is within a valid range (0 to 100 in this case).

In the doPost method, before processing the number, we call this validation method. If the number is invalid, we send an error response with the status code SC_BAD_REQUEST (400) and a message "Invalid number format". If the number is valid, we proceed with the processing.

This way, we ensure that only valid numbers are processed, preventing potential issues that could arise from processing invalid numbers. This also improves the robustness of the application as it can now handle invalid input gracefully.

References

• 197. Lack of data validation - Numbers