Blog | G5 Cyber Security

Slow Login Attempts: A Security Risk?

G5 Cyber Security

TL;DR

Yes, deliberately slow login attempts can be a security risk, opening you up to timing attacks and denial-of-service. Here’s how to protect yourself.

Understanding the Problem

When someone tries to log in, your system checks their username and password. If it takes too long to respond – even if the login fails – attackers can gather information about your system or overwhelm it. This is especially true if the time taken varies depending on whether the username exists.

Why Slow Login Attempts are a Problem

  1. Timing Attacks: Attackers measure how long it takes to respond to different login attempts (valid vs invalid usernames). This can reveal which usernames exist in your system.
  2. Denial-of-Service (DoS): If the login process is slow, an attacker can flood your server with requests, making it unavailable for legitimate users.

How to Fix It

Here’s a step-by-step guide to mitigate these risks:

1. Consistent Response Times

  1. Standardize Delay: Always take the same amount of time to respond, regardless of whether the username and password are correct or not. This prevents timing attacks.
  2. Implement a Fixed Delay: Add a small, fixed delay (e.g., 0.5 – 1 second) to all login responses.
# Example Python code (illustrative only)
import time

def check_login(username, password):
  time.sleep(0.75) # Fixed delay
  # ... your login checking logic here...
  return False # or True

2. Rate Limiting

  1. Limit Attempts: Restrict the number of login attempts allowed from a single IP address within a specific timeframe (e.g., 5 attempts in 10 minutes).
  2. Block Suspicious IPs: Temporarily block IPs that exceed the rate limit.
# Example using fail2ban configuration (Linux)
[sshd]
enabled = true
port    = ssh
logpath  = /var/log/auth.log
maxretry = 5
findtime = 600 # 10 minutes
bantime  = 3600 # 1 hour

3. Account Lockout

  1. Lock Accounts: After a certain number of failed login attempts (e.g., 5), lock the account for a period of time (e.g., 30 minutes).
  2. Require CAPTCHA: After multiple failures, present a CAPTCHA challenge to verify the user is human.

4. Strong Password Policies

  1. Enforce Complexity: Require strong passwords with a mix of uppercase and lowercase letters, numbers, and symbols.
  2. Regular Changes: Encourage users to change their passwords regularly.

5. Monitor Login Attempts

  1. Log Failed Attempts: Keep detailed logs of all failed login attempts, including the username, IP address, and timestamp.
  2. Alerting: Set up alerts to notify you of unusual activity, such as a large number of failed logins from a single IP address.

6. Web Application Firewall (WAF)

A WAF can help protect against brute-force attacks and other login-related threats by filtering malicious traffic.

Important Considerations

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