Dangling Dns in Feathersjs with Firestore

A dangling DNS entry occurs when a domain name remains registered and resolvable but no longer points to a controlled infrastructure. In a FeathersJS application that uses Google Cloud Firestore, this situation can expose both application logic and backend configuration if internal or development-only hostnames are referenced in service definitions, hooks, or configuration that is served to the client or logged unintentionally.

FeathersJS is a framework for building REST and real-time APIs with JavaScript and TypeScript. When Firestore is configured directly in service files or initialization code, developers sometimes embed project-specific hostnames, emulator endpoints, or internal bucket references. If these references are exposed—such as through error messages, debug logs, or misconfigured service metadata—an attacker can infer internal architecture or identify unused internal hostnames that resolve to unexpected destinations.

The combination of FeathersJS services and Firestore can inadvertently create a path for information disclosure if the application serves configuration that includes DNS-resolvable but unused hostnames. For example, referencing a Firestore emulator URL like http://firestore-emulator.local in client-side code or logs can reveal internal naming conventions. If that hostname later becomes dangling—pointing to an unclaimed or repurposed infrastructure—it may resolve to an attacker-controlled system, enabling redirection or confusion in environments where hostname resolution is used for service discovery or routing.

Additionally, misconfigured CORS settings or service hooks in FeathersJS can amplify exposure. A hook that logs incoming requests and includes host headers or origin values might record dangling DNS names if the application is deployed behind a load balancer or API gateway that forwards traffic through multiple internal hostnames. These logs can be harvested to map the application’s expected internal endpoints, and a dangling hostname that still resolves can be used in follow-up attacks such as SSRF or internal service probing.

Firestore security rules and Firestore emulators are designed for development and testing, but referencing emulator addresses or internal project hostnames in production code increases risk. If a FeathersJS service initializes Firestore with an emulator host that later becomes unavailable or repurposed, the mismatch between expected and actual endpoints can lead to unpredictable behavior and information leakage through error stacks or client-side debugging outputs.

To mitigate these risks, ensure that all DNS references in FeathersJS services are actively maintained and point only to intended, controlled infrastructure. Avoid embedding internal or development-only hostnames in client-accessible code, logs, or configuration. Use environment variables for Firestore project and host configuration, and validate that no dangling references remain in the codebase or deployment artifacts. Regularly audit service definitions and logs for unexpected hostname references, and apply principle of least privilege to Firestore access to limit the impact of any accidental exposure.

Remediation focuses on removing hardcoded or internal DNS references from FeathersJS service logic and configuration, ensuring that Firestore connections use stable, controlled endpoints managed through environment variables. Below are concrete examples for a FeathersJS service that securely initializes Firestore and uses parameterized configuration to avoid dangling DNS issues.

First, define environment variables for Firestore configuration. This keeps hostnames and project IDs out of source code and allows runtime configuration based on deployment environment.

// .env.production
FIRESTORE_PROJECT_ID=my-production-project
FIRESTORE_HOST=firestore.googleapis.com
NODE_ENV=production

Next, initialize Firestore in your FeathersJS app using these environment variables, and avoid referencing emulator hosts in production code.

// src/app.js
const feathers = require('@feathersjs/feathers');
const { initializeApp } = require('firebase-admin/app');
const { getFirestore } = require('firebase-admin/firestore');

const app = feathers();

const firestoreApp = initializeApp({
  projectId: process.env.FIRESTORE_PROJECT_ID,
  // Do not set 'host' or 'emulator_host' in production
}, 'firestore-admin');

Access Firestore instance safely within services without embedding hostnames:

// src/services/items/items.service.js
const { Service } = require('feathersjs-sequelize');
const { getFirestore } = require('firebase-admin/firestore');

class ItemsService extends Service {
  constructor(options) {
    super(options);
    this.firestore = getFirestore();
    this.collection = this.firestore.collection('items');
  }

  async find(params) {
    const snapshot = await this.collection.get();
    return snapshot.docs.map(doc => ({ id: doc.id, ...doc.data() }));
  }
}

module.exports = function (app) {
  app.use('/items', new ItemsService({}));
};

If you must use an emulator during development, restrict its use to non-production environments and ensure the emulator hostname is not exposed to clients.

// src/app.js (development only)
if (process.env.NODE_ENV === 'development') {
  const firestoreApp = initializeApp({
    projectId: process.env.FIRESTORE_PROJECT_ID,
  }, 'firestore-emulator');
  firestoreApp.firestore().settings({ host: 'localhost:8080', ssl: false });
}

Audit your service files and configuration for any remaining references to internal hostnames or emulator settings that could become dangling. Use CI checks to flag hardcoded hostnames and enforce that production configurations rely solely on managed environment variables.