Stop Brute Force Attacks: Web Authentication Security

TL;DR

Brute force attacks try to guess usernames and passwords repeatedly. To stop them, use strong passwords, limit login attempts, implement account lockout, add multi-factor authentication (MFA), monitor for suspicious activity, and keep your software up to date.

How Brute Force Attacks Work

Brute force attacks are a simple but effective method hackers use. They essentially try every possible combination of usernames and passwords until they find the right one. This can be automated using tools that rapidly test many credentials.

Protecting Your Web Application: A Step-by-Step Guide

1. Enforce Strong Password Policies
• Minimum length (at least 12 characters is recommended).
• Require a mix of uppercase and lowercase letters, numbers, and symbols.
• Disallow common passwords or easily guessable information (e.g., ‘password’, birthdays).
• Consider using a password strength meter during registration/change password.
2. Limit Login Attempts

Restrict the number of failed login attempts from a single IP address or user account within a specific timeframe.

• After exceeding the limit, temporarily block further attempts (e.g., for 5-15 minutes).
• Implement rate limiting on your authentication endpoints. Many web frameworks have built-in features for this.

# Example using Flask and a simple decorator

from flask import request, abort
import time

login_attempts = {}
MAX_ATTEMPTS = 5
BLOCK_DURATION = 60 # seconds

def limit_login_attempts(f):
    def decorated(*args, **kwargs):
        ip_address = request.remote_addr
        if ip_address in login_attempts:
            if login_attempts[ip_address]['attempts'] >= MAX_ATTEMPTS and time.time() - login_attempts[ip_address]['last_attempt'] < BLOCK_DURATION:
                abort(429, 'Too Many Login Attempts')
        else:
            login_attempts[ip_address] = {'attempts': 0, 'last_attempt': time.time()}
        login_attempts[ip_address]['attempts'] += 1
        return f(*args, **kwargs)
    return decorated

3. Implement Account Lockout

After a certain number of failed login attempts (e.g., 5), lock the account for a specified period (e.g., 30 minutes).

• Notify the user about the lockout and provide instructions on how to unlock their account (e.g., via email).
• Store lockout timestamps in your database.
4. Use Multi-Factor Authentication (MFA)

Require users to provide a second form of verification, such as:

• One-Time Passwords (OTP) sent via SMS or email.
• Authenticator apps (e.g., Google Authenticator, Authy).
• Hardware security keys (e.g., YubiKey).
5. Monitor for Suspicious Activity
• Log all login attempts, including IP address, username, timestamp, and success/failure status.
• Alert administrators to unusual patterns, such as a large number of failed logins from the same IP address or multiple logins from different locations within a short timeframe.
• Consider using intrusion detection systems (IDS) to automatically detect and block malicious activity.
6. Keep Software Up-to-Date

Regularly update your web application framework, libraries, and operating system to patch security vulnerabilities.

• Enable automatic updates whenever possible.
• Subscribe to security mailing lists for the software you use to stay informed about new threats.
7. Use CAPTCHA

Implement a CAPTCHA (Completely Automated Public Turing test to tell Computers and Humans Apart) on your login page to prevent automated bots from attempting brute force attacks.

8. Consider Web Application Firewalls (WAFs)

A WAF can help protect against various web application attacks, including brute force attempts. It analyzes incoming traffic and blocks malicious requests.