Brute Force Attack in Restify with Bearer Tokens

A brute force attack against a Restify service that uses Bearer tokens attempts to discover valid tokens by systematically trying many candidate values. Because Bearer tokens are typically passed in the Authorization header (Authorization: Bearer <token>), the attack focuses on token enumeration or token generation weaknesses rather than password guessing. When token entropy is low, tokens are predictable, or token validation logic in Restify does not enforce sufficient rate-limiting or token introspection, an unauthenticated attacker can send many requests with different Bearer tokens and observe differences in HTTP response codes or response bodies to identify valid tokens.

In a black-box scan, middleBrick’s Authentication and Rate Limiting checks run parallel requests with varying Bearer token values against the Restify endpoints. If the API returns 200 OK for some tokens while others yield 401 or 403 with distinct timing or wording, this indicates the server differentiates between valid and invalid tokens. Such differential behavior can expose whether a token is valid without requiring authentication via other means. The API’s unauthenticated surface is tested, and findings are cross-referenced against the OpenAPI spec if provided; for example, if the spec defines a securitySchemes of type http with bearer but does not enforce strict token validation or recommend short-lived tokens, the scan highlights gaps between design and runtime behavior.

Specific risks amplified in this combination include token enumeration via timing differences or error messages, and privilege escalation when a low-entropy token can be guessed. If the Restify server lacks proper input validation and rate limiting, an attacker can send many requests per second (BFLA/Privilege Escalation and Rate Limiting checks) using sequences of plausible Bearer tokens. Data Exposure and LLM/AI Security checks further ensure that no sensitive information, such as API keys or PII, is inadvertently surfaced in error responses that could aid an attacker in refining token guesses. Findings are mapped to relevant portions of OWASP API Top 10 and PCI-DSS controls, emphasizing the need for strong token generation and robust validation.

Remediation focuses on ensuring Bearer tokens are unpredictable, transmitted securely, and validated uniformly. Use cryptographically secure random generators to create tokens, enforce HTTPS for all traffic, and implement consistent error responses that do not distinguish between malformed and unauthorized tokens. Configure Restify to apply global rate limiting and token introspection where applicable, and avoid leaking token validity through timing or status code differences.

Example: Secure Bearer token validation in Restify

Below is a realistic Restify server snippet that demonstrates secure handling of Bearer tokens. It uses a constant-time comparison to avoid timing leaks, returns the same generic error for invalid tokens, and enforces HTTPS in production.

const restify = require('restify');
const crypto = require('crypto');

const server = restify.createServer();
server.use(restify.plugins.requestLogger());
server.use(restify.plugins.bodyParser());

// Enforce HTTPS in production (do not accept HTTP in production)
if (process.env.NODE_ENV === 'production') {
  server.on('req', (req, res, next) => {
    if (!req.secure) {
      res.code(403).send({ error: 'invalid_token' });
      return false;
    }
    return next();
  });
}

// Simulated token store (use a secure database or a signed JWT approach in practice)
const VALID_TOKENS = new Set([
  crypto.randomBytes(32).toString('hex'), // generate once and store securely
].join('\n').split('\n'));

server.use((req, res, next) => {
  const auth = req.headers.authorization;
  if (!auth || !auth.startsWith('Bearer ')) {
    res.code(401).send({ error: 'invalid_token' });
    return next();
  }
  const token = auth.slice(7);
  // Constant-time check to avoid timing attacks
  let isValid = false;
  for (const t of VALID_TOKENS) {
    if (crypto.timingSafeEqual(Buffer.from(token), Buffer.from(t))) {
      isValid = true;
      break;
    }
  }
  if (!isValid) {
    res.code(401).send({ error: 'invalid_token' });
    return next();
  }
  req.token = token;
  return next();
});

server.get('/secure', (req, res, next) => {
  res.send({ message: 'Authenticated access granted', tokenValid: true });
  return next();
});

server.listen(8080, () => {
  console.log('Restify server listening on port 8080');
});

Operational and scanning guidance

When using the CLI, you can scan your Restify API with: middlebrick scan https://api.example.com. The scan will test unauthenticated endpoints and, if an OpenAPI spec is available, cross-reference security definitions with runtime behavior. In production, adopt continuously rotating high-entropy tokens, short lifetimes, and integrate the GitHub Action to fail builds if the risk score drops below your chosen threshold. For broader coverage across many APIs, the Pro plan adds continuous monitoring and configurable schedules so you can detect regressions before attackers do.