Broken Access Control in Loopback with Basic Auth

Broken Access Control occurs when authorization checks are missing, incomplete, or bypassed, allowing a user to access functionality or data that should be restricted. In Loopback, combining Basic Auth with weak or missing authorization logic creates a scenario where authentication alone is treated as sufficient proof of privilege. Because Basic Auth transmits a base64-encoded username:password pair on each request (without transport protection unless enforced), an authenticated user can tamper with identifiers in the request and access other users' resources if the server does not enforce ownership checks.

Consider a Loopback model Account with a REST endpoint /accounts/{id}. If the API relies only on Basic Auth to identify the caller and does not validate that the authenticated user’s ID matches the requested id, this becomes a BOLA/IDOR (Broken Object Level Authorization/Insecure Direct Object Reference) vulnerability. An attacker can change the numeric or UUID path parameter to enumerate or modify accounts, invoices, or settings that belong to other users. In black-box scanning, middleBrick tests this by submitting authenticated requests with altered identifiers and checking whether the response reveals data or allows unauthorized operations, producing findings tied to BOLA/IDOR and Property Authorization checks.

Another dimension involves privilege escalation through insecure configuration of Loopback’s built-in Role and Principal models. If roles are assigned at authentication time but never re-validated on each request, or if roles are inferred from incomplete data (for example, only checking the presence of a username in Basic Auth headers), a low-privilege user may gain admin-level access by manipulating headers or tokens. The scanner’s checks for BFLA/Privilege Escalation and Unsafe Consumption look for missing role checks, over-permissive HTTP verbs, and missing model-level scopes. Data Exposure and Encryption checks further verify whether sensitive fields are returned over unencrypted channels or inadvertently exposed in error messages when authorization fails.

SSRF and Inventory Management checks reveal additional risks when Basic Auth is used to call backend services or third-party APIs. If user-supplied URLs or credentials from Basic Auth are used to make outbound requests without strict validation, the application may be coerced into scanning internal endpoints or exfiltrating metadata. Input Validation and Rate Limiting checks ensure that identifiers, credentials, and query parameters cannot be used to bypass intended authorization boundaries. By running these 12 checks in parallel, middleBrick maps findings to frameworks such as OWASP API Top 10 and provides prioritized remediation guidance without requiring authentication or internal network access.

Remediation focuses on ensuring that authentication via Basic Auth is always paired with explicit authorization checks on every request. Do not rely on the presence of Basic Auth credentials to infer role or ownership; instead, decode the credentials, load the user context, and enforce constraints before accessing any model data.

1) Enforce ownership checks in remote methods and ACLs. For example, define a remote method that validates the authenticated user ID against the resource owner ID:

// common/models/account.json ACL snippet
{
  "accessType": "EXECUTE",
  "principalType": "USER",
  "permission": "ALLOW",
  "property": "getAccountDetails",
  "principalId": "${context.principal.id}"
}

2) Implement a custom remote method that decodes Basic Auth and verifies ownership explicitly:

// common/models/account.js
Account.getAccountDetails = function(userId, cb) {
  const currentUserId = getCurrentUserIdFromBasicAuth(this);
  if (!currentUserId) {
    const err = new Error('Unauthorized');
    err.statusCode = 401;
    return cb(err);
  }
  if (currentUserId !== userId) {
    const err = new Error('Forbidden: cannot access other user data');
    err.statusCode = 403;
    return cb(err);
  }
  Account.findById(userId, cb);
};

Account.remoteMethod(
  'getAccountDetails', {
    accepts: { arg: 'userId', type: 'string', required: true },
    returns: { arg: 'data', type: 'object' },
    http: { path: '/accounts/:userId', verb: 'get' }
  }
);

3) Use a request preprocessor to normalize user context and attach it to the context object so that subsequent ACLs and model methods can rely on verified identifiers:

// server/request-headers.js
module.exports = function(app) {
  app.before('route', function(req, res, next) {
    const auth = parseBasicAuth(req.headers.authorization);
    if (auth && auth.user) {
      req.remoteUserId = auth.user; // verified after decoding
    }
    next();
  });
};

function parseBasicAuth(header) {
  if (!header || !header.startsWith('Basic ')) return null;
  const base64 = header.split(' ')[1];
  const decoded = Buffer.from(base64, 'base64').toString('utf8');
  const [user, pass] = decoded.split(':');
  // TODO: validate user credentials against a data source
  return { user, pass };
}

4) Avoid exposing internal IDs in URLs when possible, or ensure that every lookup includes a scope filter tied to the authenticated user:

// common/models/account.js — safe find by authenticated user
Account.findByOwner = function(userId, cb) {
  Account.find({ where: { ownerId: userId } }, cb);
};

5) Configure Role-based access with explicit scopes and avoid default allow-all settings in model-config.json. Define roles such as admin and user, and ensure that remote methods check roles rather than only HTTP methods.

By combining these patterns, you ensure that Basic Auth is treated strictly as a transport identity mechanism and that every request is validated for scope, ownership, and privilege, reducing the surface area for Broken Access Control in Loopback deployments.