Zone Transfer in Feathersjs with Hmac Signatures

A Zone Transfer in the context of Feathers.js services occurs when an attacker can retrieve more records than intended, often by manipulating query parameters such as $limit or by exploiting misconfigured service routes. When Hmac Signatures are used for request authentication but are applied inconsistently or only to a subset of operations, the boundary between authorized and unauthorized data access can blur. Feathers.js is a flexible framework that allows multiple transports (REST, Socket.io) and exposes a generic service interface; if authentication via Hmac Signatures is not enforced uniformly across all service methods and hooks, an attacker may leverage a publicly exposed endpoint to perform an unauthorized zone transfer.

Consider a Feathers service that uses Hmac Signatures to sign requests but only validates those signatures on create or update operations, leaving find or get operations unchecked. An attacker who discovers a valid Hmac-signed request for a write action might infer the signing key or algorithm but then pivot to abuse the lack of signature validation on read endpoints. By crafting a request that enumerates records (e.g., /messages?$limit=1000), the attacker can extract a large zone of data, effectively performing a zone transfer. This risk is compounded if the service uses soft deletes or tenant identifiers that are not properly scoped, as the Hmac signature may not include contextual parameters that enforce tenant boundaries.

In Feathers.js, services often rely on hooks for authorization. If the Hmac signature verification is implemented as a service hook that only runs on certain methods, other methods remain vulnerable to zone transfer. For example, a find hook that checks the Hmac signature might be bypassed if the get or search paths are not explicitly protected. Attackers can exploit inconsistent enforcement by probing the API with varied query combinations, using the predictability of Hmac-signed requests to infer which endpoints are weakly guarded. Real-world attack patterns such as Insecure Direct Object References (IDOR) or Broken Object Level Authorization (BOLA) can align with missing signature checks to enable zone transfers that expose sensitive records.

Another vector involves query parameter manipulation where the Hmac signature does not cover all parameters used for data access control. If a Feathers service uses fields like userId or groupId to filter results but the Hmac payload does not bind these values, an attacker can reuse a signed request with a different context to retrieve data outside their zone. This is especially dangerous in multi-tenant applications where the Hmac key is shared across clients but the service does not validate tenant identifiers within the signed payload. The result is a zone transfer that violates isolation boundaries, potentially exposing data belonging to other users or organizations.

To detect this specific combination during a scan, middleBrick runs checks that align OpenAPI/Swagger specifications with runtime behavior, identifying where authentication mechanisms like Hmac Signatures are declared but not uniformly enforced across read, write, and management operations. The scanner looks for missing authorization hooks on sensitive methods, inconsistent scope binding, and excessive record retrieval options that facilitate zone transfers. By cross-referencing spec definitions with observed responses, middleBrick highlights where Hmac-based protections fail to constrain the data zone, providing findings mapped to OWASP API Top 10 and relevant compliance frameworks.

Remediation focuses on ensuring that Hmac Signatures are validated for every service method that accesses or modifies data, and that the signed context includes all parameters that define the data zone. Below are concrete Feathers.js code examples demonstrating how to enforce Hmac verification consistently across find, get, create, and update operations.

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

function verifyHmac(req, res, next) {
  const signature = req.headers['x-hmac-signature'];
  const timestamp = req.headers['x-request-timestamp'];
  const body = JSON.stringify(req.body);
  const message = `${timestamp}.${body}`;
  const expected = crypto
    .createHmac('sha256', process.env.HMAC_SECRET)
    .update(message)
    .digest('hex');

  if (!signature || signature !== expected) {
    return next(new Error('Invalid Hmac signature'));
  }
  // Optional: reject stale requests
  if (Math.abs(Date.now() - parseInt(timestamp, 10)) > 30000) {
    return next(new Error('Request expired'));
  }
  return next();
}

const app = express(feathers());

app.use('/messages', {
  async find(params) {
    // Signature verified via before hook
    const { $limit, $skip, query } = params.query;
    // Enforce tenant or user scope using params from verified context
    const userId = params.user && params.user.id;
    const records = await app.service('messages').Model.find({
      where: { ...query, userId },
      limit: Math.min($limit || 10, 100),
      offset: $skip || 0
    });
    return records;
  },
  async get(id, params) {
    const record = await app.service('messages').Model.findById(id, params.user);
    if (!record || record.userId !== params.user.id) {
      throw new Error('Not found');
    }
    return record;
  },
  async create(data, params) {
    data.userId = params.user.id;
    return app.service('messages').Model.create(data);
  },
  async update(id, data, params) {
    const record = await app.service('messages').Model.findById(id);
    if (!record || record.userId !== params.user.id) {
      throw new Error('Not found');
    }
    return app.service('messages').Model.update(id, data);
  }
});

app.service('messages').hooks({
  before: {
    all: [verifyHmac],
    find: [contextualScopeEnforcer],
    get: [contextualScopeEnforcer],
    create: [contextualScopeEnforcer],
    update: [contextualScopeEnforcer]
  }
});

function contextualScopeEnforcer(context) {
  if (context.method === 'find') {
    const userId = context.params.user && context.params.user.id;
    if (userId) {
      context.params.query.userId = userId;
    } else {
      throw new Error('User context required');
    }
  }
  return context;
}

In this example, verifyHmac is applied in a before hook for all methods, ensuring that every request carrying an Hmac signature is validated before data access. The hook checks the signature and optionally a timestamp to prevent replay attacks. The contextualScopeEnforcer hook binds the authenticated user’s ID into the query for find, preventing zone transfers across tenant boundaries. For get, an explicit ownership check ensures that a record can only be retrieved if it belongs to the authenticated user, mitigating IDOR risks that could otherwise facilitate unauthorized zone transfers.

For production use, store HMAC_SECRET securely and rotate keys periodically. Ensure that the Hmac signature covers all parameters that affect data scope, including tenant identifiers, and that no read path bypasses the hook chain. middleBrick’s scans can validate that Hmac verification is declared for each operation in your OpenAPI spec and that runtime behavior aligns with these protections.