Preventing Brute-Force Attacks
This article provides a technical deep dive into brute-force attack prevention
strategies, explores real-world incidents, and includes links to resources and
examples of both successful attacks and effective countermeasures.
Prevention Techniques:
1. Strong Password Policies
You must use strong, unique passwords that are not based on words or phrases in a
dictionary. Strong passwords should be at least eight characters long and contain a
mix of upper and lowercase letters, numbers, and special characters.
Avoid using common words or personal information in your passwords, as they
can be easily guessed.
Ignore the most common passwords.
Implement policies to reject weak passwords and enforce users to change their
passwords frequently.
2. Account Lockout and Rate Limiting
Limit the number of login attempts made within a certain period and lock down the
account after a certain number of login attempts. This makes it more difficult for
the attacker to guess the password.
3. Multi-Factor Authentication (MFA)
MFA provides an extra layer of security to your accounts by requiring you to
provide more than one form of authentication in addition to your password. This
could be a code sent to your phone, a biometric scan or a security token.
4. CAPTCHA Implementation
A CAPTCHA can determine whether the user is a human or a computer. You can
make it more difficult for automated brute-force attacks to succeed by requiring
users to complete a CAPTCHA before attempting to log in. Google reCAPTCHA
and hCaptcha are two widely used solutions that verify whether a login request is
made by a human or a bot.
5. IP Blacklisting and Geo-Fencing
Block repeated access from IP addresses after failed login attempts. Restrict logins
from countries where your organization doesn't operate. For example, Cloudflare's
Web Application Firewall (WAF) can automatically block IPs showing brute-force
behavior.
6. Secure Authentication Protocols
Avoid using plain-text passwords in transmission (use HTTPS). Use salted hashing
for password storage (e.g., bcrypt, Argon2). By doing this you can make attacker’s
work harder, so he must find both salt and password which doubles the process.
7. Monitor and Alert
Keep track of login activities, like the number of failed login attempts and the
failed IP addresses of users and locations. Regular monitoring helps organizations
identify and respond to brute force attacks before and as they are happening. For
example, Enterprise organizations often deploy SIEM tools such as Splunk, ELK
Stack (Elasticsearch, Logstash, Kibana), and Graylog to monitor, correlate, and
respond to security events. These platforms analyze logs from servers, firewalls,
and applications, helping identify brute-force patterns early.
8. Change default ports
Microsoft Windows OS comes with Remote Desktop Services on the default port
3389. Since this port is commonly used, it can be an easy target for brute-force
attacks against remote desktops. Similarly, the SSH service also comes with the 22
port. You can change this port to make brute force process a bit harder.
