Credential Stuffing

Credential Stuffing Overview

Credential Stuffing lets you structure authentication work so it stays readable, testable, and easy to scale. Instead of ad-hoc code, you follow a clear pattern that other developers can recognise immediately.

The key is to keep credential stuffing focused and predictable. Start from the minimal example here, then layer in only the complexity your feature actually needs.

import rateLimit from 'express-rate-limit';

const loginLimiter = rateLimit({
  windowMs: 15 * 60 * 1000,
  max: 5,
  message: 'Too many login attempts, try again later',
});

app.post('/login', loginLimiter, loginHandler);

Rate limiting login attempts is a first line of defence against brute-force attacks.

Credential Stuffing Example

// verify the caller on every protected request
function authenticate(req, res, next) {
  const token = req.headers.authorization?.replace('Bearer ', '');
  req.user = verifyToken(token); // throws if invalid
  next();
}

• Start from a minimal Credential Stuffing example and grow it only as needed.
• Keep configuration explicit so Credential Stuffing behaves the same in every environment.
• Name things clearly so teammates understand your Credential Stuffing at a glance.
• Add tests around Credential Stuffing early to lock in expected behaviour.

Authentication Cheatsheet

Quick authentication reference related to credential stuffing.

How Credential Stuffing Works

Credential Stuffing is part of proving who a user is and what they are allowed to do. Authentication verifies identity, while authorization decides access — and credential stuffing plays a specific role in that flow.

Rate limiting login attempts is a first line of defence against brute-force attacks.

• Never store or log plain-text passwords or secrets.
• Prefer short-lived tokens with refresh over long-lived ones.
• Always send credentials over HTTPS.
• Fail closed: deny access when anything is uncertain.

Security Guidance for Credential Stuffing

Security is the whole point of credential stuffing. Small mistakes — weak hashing, tokens in localStorage, missing rate limits — are exactly what attackers look for, so follow proven defaults.

Common Mistakes

• Copying credential stuffing snippets without understanding what each line does.
• Skipping error handling and edge cases when wiring up credential stuffing.
• Leaving credential stuffing untested, so regressions slip into production.
• Over-engineering credential stuffing before you actually need the extra flexibility.

Key Takeaways

• Credential Stuffing is a core part of working effectively with authentication.
• Start small and keep credential stuffing focused on a single responsibility.
• Apply consistent patterns so credential stuffing scales across your project.
• Test and document credential stuffing to keep it maintainable over time.