Broken Authentication in Loopback with Basic Auth

Loopback is a widely used Node.js framework for building APIs quickly, and Basic Auth is a simple authentication scheme that sends credentials in an HTTP header. When Basic Auth is used in Loopback without additional protections, it can lead to Broken Authentication, a common API security weakness. The risk often arises from using unencrypted transport, missing rate limiting, or improper credential validation, which exposes static or weakly protected credentials to interception or brute-force attacks.

In a black-box scan, middleBrick tests unauthenticated attack surfaces and flags Broken Authentication when endpoints accept Basic Auth credentials without enforcing HTTPS, lack account lockout or exponential backoff, or expose user enumeration through timing differences. For example, an endpoint like /api/users/me that parses an Authorization header as Basic base64(username:password) can allow attackers to harvest valid credentials if the channel is not encrypted or if weak passwords are accepted without throttling.

middleBrick checks this control as part of its Authentication and BOLA/IDOR checks. It looks for whether credentials are transmitted over non-TLS connections, whether the server responds differently to malformed credentials versus valid ones (information leakage), and whether there are no protections against credential stuffing. Because Loopback can be configured to accept Basic Auth via built-in components or custom middleware, misconfigurations—such as not requiring HTTPS or not hashing stored passwords—directly contribute to a higher risk score and findings under standards like OWASP API Top 10 and PCI-DSS.

Another relevant check is BFLA/Privilege Escalation: if a Loopback endpoint accepting Basic Auth does not verify authorization per resource instance, an attacker who obtains a low-privilege credential might access or modify data belonging to other users. middleBrick cross-references the OpenAPI spec definitions with runtime behavior to detect whether authentication is enforced consistently across routes and whether tokens or sessions derived from Basic Auth are handled securely.

To remediate Broken Authentication when using Basic Auth in Loopback, enforce HTTPS, hash credentials, and add rate limiting. Below are concrete, working examples that you can adapt to your project.

1. Enforce HTTPS in Loopback

Ensure the server only accepts secure connections and rejects HTTP. Configure the HTTPS server explicitly and disable HTTP.

// server.js
const https = require('https');
const fs = require('fs');
const loopback = require('loopback');
const app = loopback();

const options = {
  key: fs.readFileSync('/path/to/server.key'),
  cert: fs.readFileSync('/path/to/server.crt'),
};

https.createServer(options, app).listen(8443, () => {
  console.log('Loopback HTTPS server running on port 8443');
});

2. Secure Basic Auth with hashed credentials and strict validation

Do not store or compare passwords in plaintext. Use a strong hashing algorithm (bcrypt) and compare hashes safely. Define a User model with an email and a hashed password.

// common/models/user.json
{
  "name": "user",
  "base": "User",
  "idInjection": true,
  "options": { "validateUpsert": true },
  "properties": {
    "email": { "type": "string", "required": true },
    "passwordHash": { "type": "string", "required": true }
  },
  "acls": [
    { "accessType": "*", "principalType": "ROLE", "principalId": "$everyone", "permission": "DENY" }
  ]
}

// common/models/user.js
const bcrypt = require('bcrypt');
const SALT_ROUNDS = 10;

module.exports = function(User) {
  User.beforeSave = async function(next, model) {
    if (model.password) {
      model.passwordHash = await bcrypt.hash(model.password, SALT_ROUNDS);
      delete model.password;
    }
    next();
  };

  User.authenticate = async function(email, password) {
    const user = await User.findOne({ where: { email } });
    if (!user) {
      throw new Error('Invalid credentials');
    }
    const match = await bcrypt.compare(password, user.passwordHash);
    if (!match) {
      throw new Error('Invalid credentials');
    }
    // Return a minimal safe payload, avoid leaking sensitive info
    return { id: user.id, email: user.email };
  };
};

3. Add rate limiting to mitigate credential guessing

Use a built-in Loopback component or an HTTP-level limiter to reduce brute-force risk. This example uses the built-in rate limiter on the REST component.

// server.js
const loopback = require('loopback');
const app = loopback();

app.use(loopback.rest({
  normalizeHttpPath: true,
  legacyExplorer: false,
  // Configure rate limiting to protect authentication endpoints
  rateLimit: {
    windowMs: 15 * 60 * 1000, // 15 minutes
    max: 30, // limit each IP to 30 requests per windowMs
    message: 'Too many requests from this IP, please try again later.'
  }
}));

// Require HTTPS for all operations
app.use(loopback.token());
app.start = function() {
  return app.listen(8443).on('listening', () => {
    console.log('Loopback server is now listening securely on HTTPS');
  });
};

4. Validate and scope authorization for authenticated requests

Ensure that endpoints which retrieve or modify user data validate ownership and scope. For example, protect user profile endpoints so users can only access their own data.

// common/models/user.js
module.exports = function(User) {
  User.observe('access', function filterUserById(ctx, next) {
    const AccessToken = ctx.Model.app.models.AccessToken;
    if (ctx.where && ctx.where.accessTokenId) {
      AccessToken.findById(ctx.where.accessTokenId, function(err, token) {
        if (err) return next(err);
        if (!token) return next(new Error('Invalid token'));
        // Ensure the token's user ID matches the requested user ID
        if (ctx.query && ctx.query.where) {
          if (!ctx.query.where.id) ctx.query.where.id = token.userId;
        }
        next();
      });
    } else {
      next();
    }
  });
};

These steps reduce the attack surface for Basic Auth in Loopback by ensuring transport security, safe credential storage, brute-force protection, and proper authorization checks. middleBrick can validate these controls by scanning your endpoints and highlighting misconfigurations related to authentication, BOLA/IDOR, and privilege escalation.