What is a Brute Force Attack?

A brute force attack is a cyberattack method where hackers systematically try multiple combinations of usernames and passwords to gain unauthorized access to a system. These attacks exploit weak passwords and outdated security measures, making Virtual Private Servers (VPS) a prime target. Since VPS hosts critical applications and sensitive data, securing it from brute force attacks is essential.

Hackers use automated tools to try thousands or even millions of login attempts until they find the correct credentials. This can lead to compromised accounts, data breaches, financial losses, and even complete system takeover. The best defense against brute force attacks is implementing strong security measures to prevent unauthorized access.

To help you safeguard your VPS, here are ten best practices to prevent brute force attacks.

10 Best Practices to Prevent Brute Force Attacks on VPS

1. Use Strong and Complex Passwords

One of the simplest yet most effective ways to protect your VPS is to use strong passwords. A strong password should be at least 12-16 characters long and include a combination of uppercase and lowercase letters, numbers, and special characters. Avoid using easily guessable words such as "password123" or "admin." Instead, use a password manager to generate and store secure passwords.

Hackers use dictionary attacks that attempt commonly used words and phrases. By using a complex password, you reduce the chances of a successful attack. Furthermore, consider implementing passphrases—a combination of random words that are easier to remember but difficult to guess. Regularly updating your passwords and ensuring that they are unique for each service also strengthens your security.

2. Enable Two-Factor Authentication (2FA)

Two-factor authentication (2FA) adds an extra layer of security by requiring a second form of verification besides just a password. Even if an attacker manages to obtain your password, they won’t be able to access your VPS without the second authentication factor.

2FA can include:

• One-time passwords (OTP) sent via SMS or email
• Authentication apps like Google Authenticator or Authy
• Biometric verification such as fingerprint or facial recognition
• Hardware security keys

By enabling 2FA on your VPS, you significantly reduce the risk of unauthorized access, making it much harder for brute force attacks to succeed. Many VPS providers and control panels offer built-in 2FA support, so take advantage of it. Additionally, using authentication apps instead of SMS-based OTPs is recommended since SIM swapping attacks can compromise SMS security. A well-implemented 2FA system ensures that even if a hacker gains access to your password, they will be stopped in their tracks.

3. Change Default SSH Port

By default, Secure Shell (SSH) operates on port 22, which is well-known to hackers. Changing this default port makes it harder for attackers to find and exploit your SSH service. Choose a random, non-standard port (e.g., 2345, 4567) that isn't commonly used.

To change your SSH port:

1. Open the SSH configuration file: sudo nano /etc/ssh/sshd_config
2. Find the line #Port 22 and change it to a new port, such as Port 2345
3. Save the file and restart SSH: sudo systemctl restart ssh

While this method alone won't prevent brute force attacks, it acts as a deterrent by making your VPS less visible to automated scanning tools.

4. Use Fail2Ban to Block Repeated Login Attempts

Fail2Ban is a powerful security tool that monitors log files for suspicious login attempts and temporarily blocks IP addresses that exceed a set number of failed login attempts.

To install and configure Fail2Ban on a VPS:

1. Install Fail2Ban: sudo apt-get install fail2ban
2. Create a new configuration file: sudo nano /etc/fail2ban/jail.local
3. Define settings such as ban time, max retry attempts, and email notifications
4. Restart Fail2Ban: sudo systemctl restart fail2ban

Fail2Ban effectively prevents brute force attacks by banning malicious IPs before they can succeed.

5. Implement IP Whitelisting and Blacklisting

IP whitelisting allows only specific IP addresses to access your VPS, blocking all others. This is an excellent strategy for limiting login attempts to trusted users.

To whitelist an IP:

1. Edit your firewall rules: sudo ufw allow from <your-IP-address>
2. Save changes and restart your firewall

For blacklisting, you can use Fail2Ban or configure firewall rules to block known malicious IP addresses. This technique significantly reduces the number of attack attempts.

6. Use SSH Keys Instead of Password Authentication

SSH keys provide a more secure alternative to password authentication. They use a cryptographic pair of public and private keys, making brute force attacks nearly impossible.

To set up SSH key authentication:

1. Generate an SSH key pair: ssh-keygen -t rsa -b 4096
2. Copy the public key to your server: ssh-copy-id user@your-server-ip
3. Disable password authentication in your SSH configuration

Once SSH keys are set up, attackers can no longer use passwords to gain access, significantly reducing the risk of brute force attacks. Unlike passwords, SSH keys are not susceptible to guessing or brute-force attempts, as they rely on a much stronger encryption method. Even if a hacker intercepts data packets, decrypting an SSH key is practically impossible without the private key.

This method drastically minimizes unauthorized access risks and strengthens your VPS security. Furthermore, combining SSH key authentication with passphrase protection provides an extra security layer in case your private key gets compromised.

7. Monitor Login Attempts and Suspicious Activity

Regularly monitoring your VPS for unusual login attempts helps detect and prevent brute force attacks. Use tools like last and auth.log to check login history.

• View login history: last
• Check authentication

3. Change Default SSH Port

By default, Secure Shell (SSH) operates on port 22, which is well-known to hackers. Changing this default port makes it harder for attackers to find and exploit your SSH service. Choose a random, non-standard port (e.g., 2345, 4567) that isn't commonly used.

To change your SSH port:

1. Open the SSH configuration file: sudo nano /etc/ssh/sshd_config
2. Find the line #Port 22 and change it to a new port, such as Port 2345
3. Save the file and restart SSH: sudo systemctl restart ssh

While this method alone won't prevent brute force attacks, it acts as a deterrent by making your VPS less visible to automated scanning tools.

4. Use Fail2Ban to Block Repeated Login Attempts

Fail2Ban is a powerful security tool that monitors log files for suspicious login attempts and temporarily blocks IP addresses that exceed a set number of failed login attempts.

To install and configure Fail2Ban on a VPS:

1. Install Fail2Ban: sudo apt-get install fail2ban
2. Create a new configuration file: sudo nano /etc/fail2ban/jail.local
3. Define settings such as ban time, max retry attempts, and email notifications
4. Restart Fail2Ban: sudo systemctl restart fail2ban

Fail2Ban effectively prevents brute force attacks by banning malicious IPs before they can succeed.

5. Implement IP Whitelisting and Blacklisting

IP whitelisting allows only specific IP addresses to access your VPS, blocking all others. This is an excellent strategy for limiting login attempts to trusted users.

To whitelist an IP:

1. Edit your firewall rules: sudo ufw allow from <your-IP-address>
2. Save changes and restart your firewall

For blacklisting, you can use Fail2Ban or configure firewall rules to block known malicious IP addresses. This technique significantly reduces the number of attack attempts.

6. Use SSH Keys Instead of Password Authentication

SSH keys provide a more secure alternative to password authentication. They use a cryptographic pair of public and private keys, making brute force attacks nearly impossible.

To set up SSH key authentication:

1. Generate an SSH key pair: ssh-keygen -t rsa -b 4096
2. Copy the public key to your server: ssh-copy-id user@your-server-ip
3. Disable password authentication in your SSH configuration

Once SSH keys are set up, attackers can no longer use passwords to gain access, significantly reducing the risk of brute force attacks.

7. Monitor Login Attempts and Suspicious Activity

Regularly monitoring your VPS for unusual login attempts helps detect and prevent brute force attacks. Use tools like last and auth.log to check login history.

• View login history: last
• Check authentication logs: sudo cat /var/log/auth.log | grep "Failed password"

You can also configure alerts to notify you of suspicious activity in real time.

8. Restrict Root Access and Use a Non-Root User

The root account is a primary target for hackers. Disable direct root login and use a non-root user with limited privileges.

To disable root login:

1. Open the SSH config file: sudo nano /etc/ssh/sshd_config
2. Find PermitRootLogin yes and change it to PermitRootLogin no
3. Restart SSH: sudo systemctl restart ssh

This step ensures that attackers cannot target the root account directly.

9. Keep Software and System Updated

Regularly updating your VPS operating system and software patches vulnerabilities that hackers exploit in brute force attacks.

To update your system:

• Ubuntu/Debian: sudo apt update && sudo apt upgrade -y
• CentOS/RHEL: sudo yum update -y

Enable automatic updates where possible to ensure your VPS remains secure.

10. Deploy a Web Application Firewall (WAF)

A Web Application Firewall (WAF) helps block malicious traffic and brute force attacks. It analyzes incoming traffic and blocks requests that match known attack patterns.

Popular WAF solutions include:

• Cloudflare WAF
• ModSecurity
• Sucuri Firewall

A WAF acts as a strong defense layer, filtering out attackers before they even reach your VPS.

Conclusion

Brute force attacks on VPS are a serious threat, but by implementing these ten security measures, you can significantly reduce your risk. Using strong passwords, enabling 2FA, restricting access, and utilizing security tools like Fail2Ban and WAF are essential steps in safeguarding your VPS. Stay proactive, monitor your system regularly, and keep your security measures updated to ensure maximum protection against cyber threats.

Cybercriminals are constantly evolving their techniques, so staying ahead with proactive security measures is crucial. By applying these best practices, you create a resilient VPS that is well-guarded against malicious intrusion attempts. Always remember, cybersecurity is an ongoing process—keep learning, adapting, and securing your server to stay one step ahead of potential threats.