login-rate-limit.md

Implement express rate limiting for login routes

One Paragraph Explainer

Leaving higher privileged routes such as /login or /admin exposed without rate limiting leaves an application at risk of brute force password dictionary attacks. Using a strategy to limit requests to such routes can prevent the success of this by limiting the number of allow attempts based on a request property such as ip, or a body parameter such as username/email address.

An in-memory store such as Redis or MongoDB should be used in production to enforce the shared limit across application clusters.

Code example: Using express-brute

const ExpressBrute = require('express-brute');
const RedisStore = require('express-brute-redis');

const redisStore = new RedisStore({
  host: '127.0.0.1',
  port: 6379
});

// Start slowing requests after 5 failed attempts to login for the same user
const loginBruteforce = new ExpressBrute(redisStore, {
  freeRetries: 5,
  minWait: 5 * 60 * 1000, // 5 minutes
  maxWait: 60 * 60 * 1000, // 1 hour
  failCallback: failCallback,
  handleStoreError: handleStoreErrorCallback
});

app.post('/login',
  loginBruteforce.getMiddleware({
    key: function (req, res, next) {
      // prevent too many attempts for the same username
      next(req.body.username);
    }
  }), // error 403 if we hit this route too often
  function (req, res, next) {
    if (User.isValidLogin(req.body.username, req.body.password)) {
      // reset the failure counter for valid login
      req.brute.reset(function () {
        res.redirect('/'); // logged in
      });
    } else {
      // handle invalid user
    }
  }
);

What other bloggers say

From the Essential Node.js Security book by Liran Tal:

Brute-force attacks may be employed by an attacker to send a series of username/password pairs to your REST end-points over POST or another RESTful API that you have opened to implement them. Such a dictionary attack is very straight-forward and easy to execute and may be performed on any other parts of your API or page routing, unrelated to logins.