Okay, let’s get into the nitty-gritty of keeping our Express.js applications safe from those pesky brute-force attacks. It’s a bit of a cat-and-mouse game with hackers sometimes, but there are solid steps we can take to make their lives a lot harder. Let’s dive in.

First things first, what the heck is a brute-force attack? It’s one of those hacker tricks where they basically throw random combinations of usernames and passwords at your login endpoint until they hit the jackpot. If your security isn’t up to snuff, this can actually work. So, we need to take this seriously.

One of the simplest and most effective ways to stop these attacks is by implementing rate limiting. It’s all about making sure nobody makes a ridiculous number of requests to your server in a short period of time. I’ve used the express-rate-limit middleware in the past and it works like a charm. Here’s a quick setup:

const rateLimit = require('express-rate-limit');
const limiter = rateLimit({
  windowMs: 15 * 60 * 1000, // 15 minutes
  max: 100 // limit each IP to 100 requests per windowMs
});

app.use(limiter);

So, this little snippet puts a cap on requests from a single IP to 100 in 15 minutes. Tailor this to fit your app’s needs. Maybe tone it up or down depending on your user traffic.

Now, if you want to go all out, you might look into express-brute. It’s like rate-limiting on steroids, adding delay between failed attempts. Here’s a setup example:

var ExpressBrute = require('express-brute');
var MemcachedStore = require('express-brute-memcached');
var moment = require('moment');

var store;
if (config.environment === 'development') {
  store = new ExpressBrute.MemoryStore();
} else {
  store = new MemcachedStore(['127.0.0.1'], { prefix: 'NoConflicts' });
}

var failCallback = function (req, res, next, nextValidRequestDate) {
  req.flash('error', "You've made too many failed attempts. Try again " + moment(nextValidRequestDate).fromNow());
  res.redirect('/login');
};

var handleStoreError = function (error) {
  console.error(error);
  throw { message: error.message, parent: error.parent };
};

var userBruteforce = new ExpressBrute(store, {
  freeRetries: 5,
  minWait: 5 * 60 * 1000, // 5 minutes
  maxWait: 60 * 60 * 1000, // 1 hour
  failCallback: failCallback,
  handleStoreError: handleStoreError
});

app.post('/auth', userBruteforce.prevent, function (req, res, next) {
  res.send('Success');
});

This one hits the brakes hard after five failed attempts. A Fibonacci-like delay kicks in, and it even redirects users back to the login.

Strong password policies are another must. Seriously, no more “password123” nonsense. Go for at least 8 characters, mix in some uppercase, lowercase, numbers, and special symbols.

Ever seen those weird, twisty letter images online? That’s CAPTCHA, and it’s gold for blocking bots. Google’s reCAPTCHA is a more advanced version that’s even better at telling humans and bots apart. Adding a CAPTCHA challenge to your login or sign-up forms can massively cut down on attack success rates.

Next up, two-factor authentication (2FA). It adds an extra layer by requiring something you have (like a phone) in addition to something you know (like your password). So even if a hacker gets hold of your credentials, they’d still need that extra piece to get in.

Watching your application logs can be a game-changer. Keep an eye out for repeated failed logins from the same IP. It’s a strong indicator that someone’s up to no good. Regular log monitoring helps you catch attacks early.

Now, let’s get into some general security best practices:

Helmet: This little package sets HTTP headers to safeguard against many well-known web vulnerabilities.

const helmet = require('helmet');
app.use(helmet());

Keep Dependencies Updated: Regularly scan and update your dependencies using tools like npm audit or Snyk.

npm audit fix

Use HTTPS: Encrypt the data being transmitted by enabling HTTPS. Here’s a quick setup using Node’s https module.

const https = require('https');
const fs = require('fs');
const app = require('express')();
const options = {
  key: fs.readFileSync('key.pem'),
  cert: fs.readFileSync('cert.pem')
};
https.createServer(options, app).listen(443);

Proper Error Handling: Catch and manage errors properly with custom middleware.

app.use((err, req, res, next) => {
  console.error(err.stack);
  res.status(500).send('Something broke');
});

Secure Cookies: When dealing with cookies for session management, make sure they are secure and HTTPOnly.

const session = require('cookie-session');
const express = require('express');
const app = express();
const expiryDate = new Date(Date.now() + 60 * 60 * 1000); // 1 hour

app.use(session({
  name: 'session',
  keys: ['key1', 'key2'],
  cookie: {
    secure: true,
    httpOnly: true,
    domain: 'example.com',
    path: 'foo/bar',
    expires: expiryDate
  }
}));

So, there you go. These steps, when combined, create a sort of fortress around your Express.js application. It’s all about layering your security measures, keeping them updated, and staying alert to potential threats.

Remember, it’s an ongoing effort. Regularly update your security practices. Technology and attack tactics are always evolving. Make it as hard as possible for the bad guys to break in, and you’ll keep your app and its users safe.