Credential Stuffing in Loopback

Credential stuffing in Loopback applications typically exploits weak authentication controls and predictable endpoint behaviors. Attackers leverage exposed authentication endpoints to test stolen username/password combinations at scale, often targeting Loopback's default authentication flows.

The most common attack pattern targets Loopback's /auth/local endpoint, which handles username/password authentication. Since Loopback exposes this endpoint by default in many configurations, attackers can automate credential testing using tools like curl, Burp Suite, or custom scripts. A typical attack might look like:

for cred in $(cat passwords.txt); do
  curl -X POST http://target.com/auth/local \
    -H "Content-Type: application/json" \
    -d "{\"email\":\"[email protected]\",\"password\":\"$cred\"}" \
    -s | grep -q "success" && echo "Found: $cred"
done

Loopback's default configuration often lacks rate limiting on authentication endpoints, allowing attackers to make thousands of attempts per minute. The /auth/local endpoint typically returns different HTTP status codes (401 for invalid credentials vs 200 for success), providing clear feedback to attackers about valid credentials.

Another vulnerability vector is Loopback's token-based authentication. When attackers successfully authenticate, they receive JWT tokens that may have extended validity periods. Without proper token revocation mechanisms, compromised accounts remain accessible even after credential rotation. The default Loopback JWT configuration often uses long expiration times:

module.exports = {
  auth: {
    jwt: {
      secret: process.env.JWT_SECRET,
      expiration: 86400, // 24 hours by default
      issuer: 'my-app'
    }
  }
}

Loopback's user model also presents credential stuffing opportunities through its flexible schema. If applications extend the default User model without proper validation, they may inadvertently expose additional authentication vectors through custom fields or relationships. For example, an application might add a recoveryEmail field that becomes another authentication target.

The framework's built-in user management APIs, particularly /users endpoints, can leak information through timing differences. When an attacker queries /users?filter[where][email][email protected], the response time may vary based on whether the email exists, providing enumeration capabilities that complement credential stuffing attacks.

Detecting credential stuffing in Loopback requires monitoring authentication patterns and endpoint behaviors. middleBrick's black-box scanning approach is particularly effective for Loopback applications since it tests the exposed attack surface without requiring source code access.

middleBrick scans Loopback's authentication endpoints by default, testing for common credential stuffing indicators:

• Rate limiting absence on /auth/local and related endpoints
• Information leakage through HTTP status codes and response times
• Default JWT configurations with excessive expiration times
• Exposed user management APIs that enable enumeration
• Missing account lockout mechanisms

The scanner specifically targets Loopback's predictable endpoint patterns. For applications using Loopback's default authentication, middleBrick will test:

POST /auth/local
GET /users?filter[where][email]=...
GET /users/{id}
POST /users/reset-password
GET /users/exists?email=...

middleBrick's credential stuffing detection includes timing analysis to identify endpoints that leak information through response variability. Loopback applications often have measurable differences between valid and invalid user queries, which middleBrick quantifies as part of its security assessment.

The scanner also examines Loopback's authentication configuration files for insecure defaults. It checks for:

• Missing or weak bcrypt salt rounds
• Excessive JWT expiration times
• Disabled account lockout policies
• Missing rate limiting middleware

For applications using Loopback's built-in user management, middleBrick tests whether the /users endpoints are properly secured. Many Loopback applications accidentally expose user enumeration capabilities through these endpoints, providing attackers with the email lists needed for credential stuffing campaigns.

The scanner generates specific findings for Loopback applications, including:

middleBrick's findings include specific remediation guidance for Loopback applications, such as implementing Loopback's built-in rate limiting middleware or configuring proper JWT settings through the framework's configuration files.

Remediating credential stuffing in Loopback requires implementing framework-specific security controls. The most effective approach combines Loopback's built-in middleware with custom authentication guards.

First, implement rate limiting on authentication endpoints using Loopback's rateLimit middleware. Add this to your middleware.json:

{
  "auth": {
    "preTokenGeneration": ["rateLimit"],
    "postTokenGeneration": []
  }
}

Configure rate limiting in config.json:

{
  "rateLimit": {
    "auth": {
      "windowMs": 900000,
      "max": 5,
      "message": "Too many authentication attempts, please try again later."
    }
  }
}

For JWT configuration, reduce the default expiration time and implement refresh token rotation:

module.exports = {
  auth: {
    jwt: {
      secret: process.env.JWT_SECRET,
      expiration: 300, // 5 minutes instead of 24 hours
      issuer: 'my-app',
      algorithms: ['HS256']
    }
  }
}

Implement account lockout after failed attempts using Loopback's beforeRemote hooks:

module.exports = function(User) {
  User.beforeRemote('login', async function(ctx, unused, next) {
    const { email } = ctx.args.credentials;
    const user = await User.findOne({ where: { email } });
    
    if (user) {
      const failedAttempts = await User.app.models.FailedLoginAttempt.count({
        where: {
          userId: user.id,
          createdAt: { gt: new Date(Date.now() - 15 * 60000) }
        }
      });
      
      if (failedAttempts >= 5) {
        const lastAttempt = await User.app.models.FailedLoginAttempt.findOne({
          where: { userId: user.id },
          order: 'createdAt DESC'
        });
        
        const remainingTime = Math.ceil((lastAttempt.createdAt.getTime() + 15 * 60000 - Date.now()) / 1000);
        if (remainingTime > 0) {
          const err = new Error('Account temporarily locked due to multiple failed attempts');
          err.statusCode = 423;
          return next(err);
        }
      }
    }
    next();
  });

  User.afterRemoteError('login', async function(ctx, next) {
    if (ctx.error.statusCode === 401) {
      const email = ctx.args && ctx.args.credentials && ctx.args.credentials.email;
      if (email) {
        const user = await User.findOne({ where: { email } });
        if (user) {
          await User.app.models.FailedLoginAttempt.create({
            userId: user.id,
            ipAddress: ctx.req.ip
          });
        }
      }
    }
    next();
  });
};

Create a model for tracking failed attempts:

module.exports = function(FailedLoginAttempt) {
  FailedLoginAttempt.validatesPresenceOf('userId', 'ipAddress');
};

Secure user enumeration by restricting /users endpoints:

module.exports = function(User) {
  User.disableRemoteMethodByName('find');
  User.disableRemoteMethodByName('findById');
  User.disableRemoteMethodByName('findOne');
  
  User.remoteMethod('exists', {
    accepts: { arg: 'email', type: 'string', required: true },
    returns: { arg: 'exists', type: 'boolean' },
    http: { path: '/exists', verb: 'get' }
  });

  User.exists = async function(email) {
    const user = await User.findOne({ where: { email } });
    return !!user;
  };
};

Implement CAPTCHA or similar challenges after multiple failed attempts:

const { Recaptcha } = require('recaptcha');
const recaptcha = new Recaptcha(process.env.RECAPTCHA_SECRET);

Add to your login method:

async function login(credentials) {
  const failedAttempts = await this.app.models.FailedLoginAttempt.count({
    where: { ipAddress: ctx.req.ip, createdAt: { gt: new Date(Date.now() - 1 * 60000) } }
  });
  
  if (failedAttempts >= 3) {
    const captchaResponse = ctx.args.credentials.captcha;
    const verified = await recaptcha.verify(captchaResponse);
    if (!verified) {
      throw new Error('CAPTCHA verification failed');
    }
  }
  
  // Continue with authentication
}

Finally, integrate middleBrick's CLI into your CI/CD pipeline to continuously test for credential stuffing vulnerabilities:

npm install -g middlebrick
middlebrick scan https://api.yourapp.com --output json --fail-below B