Need

Implementation of a robust and secure mechanism to prevent brute force attacks on promotional code credentials.

Context

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

Description

Non compliant code

        import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

public class PromoCodeServlet extends HttpServlet {
    private static final long serialVersionUID = 1L;

    protected void doPost(HttpServletRequest request, HttpServletResponse response) {
        String promoCode = request.getParameter("promoCode");

        if (isValidPromoCode(promoCode)) {
            // Process the promo code
        } else {
            // Invalid promo code
        }
    }

    private boolean isValidPromoCode(String promoCode) {
        // Check if the promo code is valid
        // This is a placeholder, replace with actual validation logic
        return promoCode.equals("VALID_CODE");
    }
}
        
        

The above Java Servlet code snippet takes a promotional code as input from an HTTP POST request and checks if it's valid. The doPost method retrieves the promoCode parameter from the request, and then calls the isValidPromoCode method to check if the provided promo code is valid.

The vulnerability lies in the isValidPromoCode method. This method simply checks if the input promotional code equals a hardcoded "VALID_CODE". There is no protection against brute force attacks. An attacker could potentially make multiple HTTP POST requests with different promotional codes until they find the valid one.

This vulnerability exposes the application to the risk of unauthorized access or potentially fraudulent activity. For example, an attacker could gain access to promotional benefits that they are not entitled to.

Moreover, this code does not implement any rate-limiting or account lockout mechanisms after a certain number of failed attempts. This allows an attacker to make an unlimited number of attempts at guessing the promotional code, further increasing the risk of a successful brute force attack.

To mitigate this vulnerability, the application should implement measures such as CAPTCHA, account lockout, or delay mechanisms after a certain number of failed attempts. This will help to protect against automated brute force attacks.

Steps

• Implement rate limiting to prevent brute force attacks
• Use a strong and secure algorithm to generate and validate promo codes
• Implement CAPTCHA or other challenge-response mechanisms to verify user input
• Implement account lockout mechanism after a certain number of failed attempts
• Implement logging and monitoring to detect and respond to suspicious activities
• Regularly update and patch the application to address any security vulnerabilities

Compliant code

        import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import com.google.common.util.concurrent.RateLimiter;

public class PromoCodeServlet extends HttpServlet {
    private static final long serialVersionUID = 1L;
    private static final RateLimiter rateLimiter = RateLimiter.create(5.0);  // 5 attempts per second per user
    private static final int MAX_ATTEMPTS = 5;  // Max attempts before lockout
    private static final Map attempts = new HashMap<>();  // Store attempts per user

    protected void doPost(HttpServletRequest request, HttpServletResponse response) {
        String promoCode = request.getParameter("promoCode");
        String userIP = request.getRemoteAddr();

        if (!rateLimiter.tryAcquire()) {
            response.sendError(HttpServletResponse.SC_TOO_MANY_REQUESTS);
            return;
        }

        if (attempts.getOrDefault(userIP, 0) >= MAX_ATTEMPTS) {
            response.sendError(HttpServletResponse.SC_FORBIDDEN);
            return;
        }

        if (isValidPromoCode(promoCode)) {
            // Process the promo code
            attempts.remove(userIP);  // Reset attempts on success
        } else {
            // Invalid promo code
            attempts.put(userIP, attempts.getOrDefault(userIP, 0) + 1);  // Increment attempts on failure
        }
    }

    private boolean isValidPromoCode(String promoCode) {
        // Check if the promo code is valid
        // This is a placeholder, replace with actual validation logic
        return promoCode.equals("VALID_CODE");
    }
}
        
        

The updated code now includes a rate limiter that limits the number of promo code attempts to 5 per second per user. This is done using Google's Guava library's RateLimiter class. If a user exceeds this limit, the server responds with a 429 (Too Many Requests) error.

The code also keeps track of the number of failed attempts per user (identified by IP address). If a user makes more than 5 failed attempts, the server responds with a 403 (Forbidden) error, effectively locking out the user.

On successful validation of a promo code, the user's attempt count is reset.

This approach helps to mitigate brute force attacks by limiting the rate at which promo codes can be guessed and by locking out users who make too many failed attempts. However, it's important to note that this is just one layer of defense and should be used in conjunction with other security measures such as strong promo code generation and validation algorithms, CAPTCHA mechanisms, and regular security updates and patches.

References

• 330. Lack of protection against brute force attacks - Credentials