TL;DR
No system is completely immune to brute force attacks given enough time and resources. However, you can make it incredibly difficult and costly for attackers by using a combination of techniques like strong passwords, account lockouts, multi-factor authentication (MFA), rate limiting, CAPTCHAs, and intrusion detection systems.
How to Protect Against Brute Force Attacks
- Strong Password Policies: This is your first line of defence.
- Length: Passwords should be at least 12 characters long, ideally more.
- Complexity: Use a mix of uppercase and lowercase letters, numbers, and symbols.
- Uniqueness: Discourage password reuse across different services.
- Regular Changes: Enforce periodic password updates (e.g., every 90 days).
- Account Lockout Policies: Prevent attackers from repeatedly trying passwords.
- Threshold: After a certain number of failed login attempts (e.g., 5-10), lock the account for a period.
- Duration: Lockout durations should increase with each subsequent lockout attempt (exponential backoff). For example, 5 minutes after the first lockout, 30 minutes after the second, and so on.
- Notification: Alert users when their account is locked.
- Multi-Factor Authentication (MFA): Add an extra layer of security beyond just a password.
- Types: Common MFA methods include one-time codes sent via SMS, authenticator apps (Google Authenticator, Authy), or hardware security keys.
- Implementation: Enable MFA wherever possible, especially for critical accounts and systems.
- Rate Limiting: Limit the number of login attempts from a single IP address within a specific timeframe.
- Configuration: Configure your web server or application firewall to restrict requests. For example, allow only 5 login attempts per minute from each IP address.
- Example (using `fail2ban` on Linux):
sudo fail2ban-client set sshd-ips 192.168.1.100 banip
- CAPTCHAs: Distinguish between humans and bots.
- Implementation: Use CAPTCHAs on login forms, especially if you suspect automated attacks.
- Considerations: Modern CAPTCHAs (like reCAPTCHA v3) are less intrusive than traditional image-based ones.
- Intrusion Detection/Prevention Systems (IDS/IPS): Monitor for suspicious activity.
- Rules: Configure IDS/IPS to detect patterns associated with brute force attacks, such as a large number of failed login attempts from the same IP address.
- Alerting: Set up alerts to notify you when a potential attack is detected.
- Web Application Firewall (WAF): Protect web applications from common attacks, including brute force.
- Rulesets: WAFs often have pre-built rulesets to mitigate brute force attempts.
- Custom Rules: You can also create custom rules tailored to your specific application.
- Use a Reputable Login System/Library: Avoid writing your own authentication system from scratch.
- Security Audits: Well-established libraries have been thoroughly tested and audited for security vulnerabilities.
- Monitor Logs Regularly: Check logs for failed login attempts, account lockouts, and other suspicious activity.
- Tools: Use log analysis tools to automate the process of identifying potential attacks.
Remember that a layered approach is best. Combining multiple security measures will significantly increase your protection against brute force attacks.