How to Implement Rate Limiting to Protect Against Brute Force Attacks

November 26, 20235 min read

Brute force attacks involve an attacker submitting many passwords or passphrases with the hope of eventually guessing a user’s credentials correctly. Implementing rate limiting is one of the effective ways to mitigate such attacks. Below is a detailed guide on how to implement rate limiting to protect your system against brute force attacks.

Understanding Rate Limiting

Rate limiting restricts the number of requests a user can make to a server within a given timeframe. It’s crucial in preventing servers from being overwhelmed by too many requests and in protecting accounts from brute force attacks.

Planning Your Rate Limiting Strategy

Identifying Sensitive Endpoints:

  • Login pages: The most obvious target for brute force attacks.
  • Password reset pages: Another potential vector for attacks as they also deal with authentication.
  • API endpoints: Revolving around user data or actions that require authentication.

Defining Limit Thresholds:

You need to find a balance between user convenience and security. If the threshold is too low, it could disturb legitimate users. If it’s too high, it might not effectively block brute force attacks.

  • Request limit: Determine the maximum number of attempts (usually low for login attempts).
  • Time window: Set the duration within which the set number of attempts is allowed (e.g., 5 attempts per 15 minutes).

Implementing Rate Limiting Mechanisms

Server-Side Rate Limiting:

Implement server-side controls to count the number of failed login attempts per user/IP address and limit further attempts after a threshold is reached.

By IP Address:

  • Track the number of attempts from an IP address.
  • Temporarily block the IP address after exceeding the limit.

By User Account:

  • Count attempts against a specific user account.
  • Lock the account for a set period after too many failed login attempts.

Distributed Systems Considerations:

If your system is distributed, ensure all nodes share the rate limiting information to prevent an attacker from simply switching nodes.

  • Centralized Data Store: Use a shared database or a cache like Redis to store counters across the system.
  • Synchronization: Keep rate-limit counters synchronized across servers.

Choosing Rate Limiting Algorithms:

  • Fixed Window Counter: Resets the counter at fixed intervals, which can allow bursts of traffic at the edges of time windows.
  • Sliding Log Algorithm: Records timestamps of each request in a log, allowing dynamic time window adjustments.

Client Feedback:

  • Inform users about the remaining number of attempts they have.
  • Provide a lockout time if they hit the limit.

Technical Implementation


Develop or utilize existing middleware for web frameworks that enforce rate limiting. For instance, in an Express.js application, middleware like express-rate-limit can be used.

const rateLimit = require('express-rate-limit');
const limiter = rateLimit({
windowMs: 15 * 60 * 1000, // 15 minutes
max: 5 // limit each IP to 5 requests per windowMs
app.use('/login', limiter);

Utilizing a Proxy:

Employ a reverse proxy such as Nginx or a service like Cloudflare that offers built-in rate limiting features.

Integration with Authentication System:

Ensure your authentication flow includes the rate limiting mechanism, usually provided through hooks or callbacks.

Testing Your Rate Limiting System

Simulated Attacks:

Perform simulated brute force attacks to see how the system behaves and ensure it blocks excessive attempts as expected.

Adjusting Thresholds:

Monitor the user’s feedback and access logs to adjust thresholds in a way that avoids disrupting legitimate users while keeping attackers at bay.

Additional Protective Measures

While rate limiting is crucial, additional methods should further enhance security against brute force attacks.

  • CAPTCHA: Adding CAPTCHAs after several failed attempts makes automated attacks harder.
  • Two-Factor Authentication (2FA): Offers an additional security layer even if a password is compromised.
  • Account Lockout Policies: Define policies where after N attempts, the account gets locked requiring manual intervention.

Monitoring and Alerts

Continuous monitoring is critical to adapting to new threats and challenges.

  • Logging: All login attempts should be logged along with the associated metadata.
  • Alert System: Implement an alert system to notify administrators of suspicious activities.

Implementing rate limiting is a part of a defense-in-depth strategy. While no single method is foolproof, combining several layers of security significantly increases the resilience of a system against brute force and other types of cyberattacks. Regularly review your security policies to keep up with the evolving threat landscape.