Need

Enforcement of rate limiting to control user interaction frequency, including limits on password change requests

Context

Description

// --- Rate limiting ---
import javax.servlet.*;
import javax.servlet.http.*;

public class NoRateLimitServlet extends HttpServlet {

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

**Rate limiting:** The above Java servlet code is vulnerable to DDoS attacks because it doesn't implement any rate limiting mechanism. The `doPost` method reads the "userContent" parameter from the request and processes it without checking the frequency of the requests from a particular user or IP address. This means that an attacker can send a large number of requests in a short period of time, leading to a Denial of Service (DoS) attack. This can cause the server to become overwhelmed with requests, leading to slow response times for other users, or in severe cases, causing the server to crash. In addition, this could also be exploited to perform a Brute Force attack, where an attacker attempts to guess a user's password by systematically trying every possible combination until finding the correct one. Without rate limiting, an attacker could make an unlimited number of attempts in a very short period of time. Therefore, it's crucial to implement a rate limiting mechanism to protect the system from such attacks. **Password change limit:** In the above code, `ChangePasswordServlet` is a servlet that handles password change requests. It takes in three parameters from the client - "username", "oldPassword", and "newPassword". It first retrieves the user from the database using the username. If the user exists and the old password matches the current password of the user, it updates the password in the database with the new password. The vulnerability here is that there is no limit on the number of password change requests a user can make in a day. An attacker could potentially exploit this by repeatedly changing the password and causing a denial of service or even potentially guessing the password if there are no other security measures in place like account lockouts or captcha.

// --- Rate limiting ---
import javax.servlet.*;
import javax.servlet.http.*;
import java.util.concurrent.TimeUnit;
import com.google.common.util.concurrent.RateLimiter;

public class RateLimitServlet extends HttpServlet {
...

**Rate limiting:** The above code implements a rate limiting mechanism using Google's Guava library, which provides a RateLimiter class that uses the token bucket algorithm. The `RateLimiter.create(5.0)` creates a RateLimiter that allows 5 requests per second. In the `doPost` method, `rateLimiter.tryAcquire(1, TimeUnit.SECONDS)` is used to try to acquire a permit. If a permit is not available (i.e., the rate limit has been exceeded), it returns false immediately. In this case, the servlet responds with an HTTP 429 Too Many Requests status code and returns without processing the request. If a permit is available, the method returns true and the servlet continues to process the request. This approach effectively limits the rate at which a user can make requests to the servlet, mitigating the risk of denial-of-service attacks and ensuring fair usage of resources. Please note that this is a simple implementation and may need to be adjusted based on your specific requirements. For example, you might want to implement different rate limits for different types of requests or user roles, or store the rate limit information in a persistent storage to enforce the rate limit across multiple instances of the servlet. **Password change limit:** The updated code now includes a password change limit policy. This policy is enforced by tracking the number of password change requests made by each user. A `HashMap` named `passwordChangeCounter` is used to store the number of password change requests made by each user. The key is the username and the value is the number of password change requests. When a password change request is made, the code first checks if the user exists and if the old password is correct. If these conditions are met, the code then checks the `passwordChangeCounter` to see how many password change requests the user has made. If the user has made more than or equal to the maximum number of password changes allowed per day (`MAX_PASSWORD_CHANGES_PER_DAY`), the code returns an error message and does not allow the password change. If the user has not exceeded the limit, the password is changed, the user's password change count is incremented in the `passwordChangeCounter`, and a success message is returned. This policy helps to prevent abuse of the password change feature and enhances the security of the application.

References