Arp Spoofing in Feathersjs with Hmac Signatures

Arp spoofing is a Layer 2 network 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 service. In a Feathersjs application that uses Hmac Signatures for request authentication, arp spoofing can undermine integrity even when Hmac is used, because the attack can redirect traffic to an adversary-controlled host without invalidating the Hmac itself.

Consider a Feathersjs service that validates Hmac signatures on incoming requests. The Hmac is usually computed over a canonical set of headers and the request body, using a shared secret. If an attacker performs arp spoofing between the client and the server, they can intercept and alter the HTTP payload in transit. Because the Hmac is computed client-side before transmission, the attacker cannot forge a valid Hmac for modified content without the secret. However, the attacker can still execute a man-in-the-middle (MITM) relay: pass the original request to the legitimate server and forward the server’s response back to the client. In this relay scenario, the Hmac remains valid, but the channel is compromised, enabling session hijacking or credential theft. The vulnerability is not that Hmac is broken, but that arp spoofing exposes the risk of transparent relay attacks when transport-layer confidentiality is missing.

Furthermore, if the Feathersjs service accepts connections on multiple network interfaces or in environments where Layer 2 isolation is weak (e.g., shared VLANs or containers), an attacker on the same subnet can inject forged ARP replies to redirect traffic to themselves. The server, seeing the spoofed ARP, sends responses to the attacker. If the attacker also blocks or modifies traffic, the client may not detect the breach because the Hmac verification passes on the server’s side. This highlights that Hmac signatures protect against tampering but do not prevent interception or replay unless combined with transport security. The risk is particularly acute in development or containerized environments where network segmentation is less strict.

To contextualize, this pattern maps to OWASP API Top 10 controls around authentication and integrity. While Hmac provides integrity, the threat model must include network-layer threats like arp spoofing. For example, an attacker could leverage tools like arpspoof to position themselves in the path, then attempt to capture tokens or session identifiers that are not protected by encryption. middleBrick scans detect such exposures under Data Exposure and Input Validation checks, emphasizing that Hmac alone is insufficient without transport-layer protections.

Remediation focuses on ensuring that Hmac signatures are verified securely and that transport-layer confidentiality is enforced to mitigate arp spoofing risks. Below are concrete Feathersjs examples that demonstrate best practices.

1. Enforce HTTPS and Hmac verification middleware

Always terminate TLS at the edge and configure Feathersjs to reject non-HTTPS requests in production. Combine this with a custom hook that validates Hmac signatures using a strong algorithm like HmacSHA256.

const feathers = require('@feathersjs/feathers');
const express = require('@feathersjs/express');
const crypto = require('crypto');
const app = express(feathers());

function verifyHmac(req, res, next) {
  const signature = req.headers['x-api-signature'];
  const timestamp = req.headers['x-request-timestamp'];
  const nonce = req.headers['x-request-nonce'];
  const body = JSON.stringify(req.body);
  const message = [timestamp, nonce, body].join('|');

  if (!signature) {
    return next(new Error('Missing signature'));
  }

  const expected = crypto.createHmac('sha256', process.env.HMAC_SECRET)
    .update(message)
    .digest('hex');

  // Use timing-safe compare to prevent timing attacks
  if (!crypto.timingSafeEqual(Buffer.from(signature), Buffer.from(expected))) {
    return next(new Error('Invalid signature'));
  }

  // Reject stale requests (e.g., older than 5 minutes)
  const now = Math.floor(Date.now() / 1000);
  if (Math.abs(now - parseInt(timestamp, 10)) > 300) {
    return next(new Error('Request expired'));
  }

  next();
}

app.configure(express.rest());
app.use(verifyHmac);
app.configure('/api/secure', require('./secure-service'));

2. Include additional context in the Hmac to bind to the request path

To prevent request smuggling or path confusion, incorporate the request URL path into the Hmac input. This ensures that a captured signature cannot be reused against a different endpoint.

function verifyHmacWithPath(req, res, next) {
  const signature = req.headers['x-api-signature'];
  const timestamp = req.headers['x-request-timestamp'];
  const nonce = req.headers['x-request-nonce'];
  const body = JSON.stringify(req.body);
  const path = req.path;
  const method = req.method;
  const message = [method, path, timestamp, nonce, body].join('|');

  if (!signature) {
    return next(new Error('Missing signature'));
  }

  const expected = crypto.createHmac('sha256', process.env.HMAC_SECRET)
    .update(message)
    .digest('hex');

  if (!crypto.timingSafeEqual(Buffer.from(signature), Buffer.from(expected))) {
    return next(new Error('Invalid signature'));
  }

  next();
}

3. Use environment-managed secrets and rotate periodically

Store Hmac secrets in environment variables or a secrets manager, and rotate them according to a defined schedule. Avoid hardcoding secrets in source files. The examples above reference process.env.HMAC_SECRET, which should be injected securely at runtime.

4. Combine with network-level protections

While Feathersjs handles application-layer integrity, mitigate arp spoofing by enforcing HTTPS, using HSTS headers, and isolating services via network policies. middleBrick’s scans can validate that these controls are present and correctly configured.