Arp Spoofing in Fiber with Jwt Tokens

Arp Spoofing is a Layer 2 attack where an attacker sends falsified ARP messages to associate their MAC address with the IP address of another host, typically the gateway or another API server. In a Fiber-based API environment that relies on JWT tokens for authentication, Arp Spoofing does not directly break the cryptographic integrity of the tokens, but it creates conditions that undermine the trust chain used by JWT validation. When an attacker successfully spoofs the gateway or an upstream service, requests from the victim service can be intercepted, redirected, or modified before they reach the intended API endpoint.

If the victim service uses HTTP rather than HTTPS, an attacker who is in a position to ARP spoof can observe and capture JWT tokens transmitted in request headers, such as Authorization: Bearer <token>. Even when HTTPS is used, ARP spoofing can facilitate a man-in-the-middle position that enables the attacker to inject malicious requests or responses, potentially leveraging trust relationships between services that rely on IP-based network boundaries for implicit trust. In microservice architectures where services communicate internally using JWT tokens without additional mutual TLS, ARP spoofing exposes the risk of token theft and request tampering.

middleBrick scans for SSRF and related network exposure patterns that can make ARP spoofing more effective in practice. Although the scan does not test internal Layer 2 attacks directly, findings such as missing encryption, lack of strict transport enforcement, and overly permissive service-to-service communication rules increase the effective attack surface for token interception via ARP spoofing. By correlating unauthenticated endpoint exposure with weak transport assumptions, middleBrick helps identify where JWT token usage does not sufficiently mitigate network-level threats.

To reduce the risk of token interception via ARp spoofing, ensure that all communication involving JWT tokens is protected with strong transport security and strict validation. In Fiber, enforce HTTPS for all routes and service-to-service calls, and validate JWT tokens on every request using a verified middleware implementation.

Enforce HTTPS and secure transport

Configure your Fiber application to redirect HTTP to HTTPS and terminate TLS at the edge. This prevents tokens from being transmitted in cleartext where ARP spoofing can intercept them.

const fiber = require('fiber')();

// Enforce HTTPS redirects
fiber.all('*', (c) => {
  if (c.protocol !== 'https') {
    c.redirect(`https://${c.hostname}${c.path}`);
  }
});

Validate JWT tokens on each request

Use a robust JWT validation middleware that verifies the signature, issuer, audience, and expiration. Avoid relying on network position or IP-based trust. Below is an example using jsonwebtoken with Express-compatible patterns adapted to Fiber-style handlers.

const jwt = require('jsonwebtoken');

function verifyToken(c) {
  const authHeader = c.get('Authorization');
  if (!authHeader || !authHeader.startsWith('Bearer ')) {
    c.status(401);
    return null;
  }
  const token = authHeader.split(' ')[1];
  try {
    const decoded = jwt.verify(token, process.env.JWT_PUBLIC_KEY, {
      algorithms: ['RS256'],
      issuer: 'https://auth.example.com',
      audience: 'fiber-api',
  });
    c.locals.user = decoded;
    return decoded;
  } catch (err) {
    c.status(401);
    return null;
  }
}

// Apply to protected routes
fiber.get('/api/protected', (c) => {
  const user = verifyToken(c);
  if (!user) return;
  c.json({ message: 'Access granted', user: user.sub });
});

Principle of least privilege and network segmentation

Even with JWT validation, limit internal service communication to only necessary paths and enforce strict mTLS where possible. Do not rely on JWTs alone to protect against a compromised network path. Use service mesh or network policies to restrict which services can initiate connections, reducing the impact of an ARP spoofing event.

Logging and anomaly detection

Log token validation failures and monitor for unusual patterns, such as repeated invalid tokens or requests from unexpected source IPs within the same subnet. These can be indicators of probing or active ARP spoofing attempts.

fiber.use((c, next) => {
  next();
  if (c.status() !== 200) {
    console.warn('Unauthorized access attempt', {
      ip: c.ip,
      path: c.path,
      method: c.method,
    });
  }
});