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Improper control of interaction frequency

Need​

Enforcement of rate limiting to control user interaction frequency

Context​

  • Usage of Java for building cross-platform applications
  • Usage of javax.servlet for Java web application development
  • Usage of javax.servlet.http for handling HTTP requests and responses in Java web applications

Description​

Non compliant code​

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");
        // Process the user content
    }
}

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.

Steps​

  • Implement rate limiting mechanism to restrict the number of requests a user can make within a certain time period.
  • Identify the appropriate rate limit threshold based on the system's requirements and expected user behavior.
  • Use a reliable and efficient algorithm to track and enforce the rate limit, such as token bucket algorithm or sliding window algorithm.
  • Store the rate limit information for each user, such as the number of requests made and the timestamp of the last request, in a persistent storage.
  • Check the rate limit for each incoming request and compare it with the user's rate limit information stored in the persistent storage.
  • If the user has exceeded the rate limit, return an appropriate error response (e.g., HTTP 429 Too Many Requests) and prevent further processing of the request.
  • Consider implementing different rate limits for different types of requests or user roles, if necessary.
  • Monitor and log rate limit violations for analysis and troubleshooting purposes.
  • Regularly review and adjust the rate limit thresholds based on system performance and user behavior patterns.

Compliant code​

import javax.servlet.*;
import javax.servlet.http.*;
import java.util.concurrent.TimeUnit;
import com.google.common.util.concurrent.RateLimiter;

public class RateLimitServlet extends HttpServlet {

    private final RateLimiter rateLimiter = RateLimiter.create(5.0); // permits per second

    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        if (!rateLimiter.tryAcquire(1, TimeUnit.SECONDS)) {
            response.setStatus(HttpServletResponse.SC_TOO_MANY_REQUESTS);
            return;
        }

        String userContent = request.getParameter("userContent");
        // Process the user content
    }
}

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.

References​

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