Open Redirect in Restify with Mongodb

An Open Redirect in a Restify service that uses MongoDB can occur when a URL parameter controlling the redirect target is not strictly validated and is reflected in the response without an allowlist. An attacker may supply a malicious external address, causing the Restify server to redirect users, which can be abused for phishing or to bypass origin-based trust checks. Even though MongoDB is a database and not directly responsible for HTTP redirects, its role becomes relevant when Restify builds redirect URLs from data stored in MongoDB (for example, a user profile storing a preferred landing page or a dynamic redirect mapping). If those stored values are user-controlled and are rendered into Location headers without validation, the application can be tricked into redirecting to arbitrary destinations.

In practice, this often happens when a Restify route reads a document from MongoDB and uses a field such as redirectUrl or next directly from the document to construct a response redirect. Without a strict allowlist or canonicalization, an attacker can poison the stored value or supply an attacker-controlled query parameter that overrides the intended target. Because MongoDB documents may contain URLs intended for post-login flows or branding links, failing to treat them as untrusted input creates a server-side open redirect that appears to originate from a trusted domain.

Additionally, if the Restify API also exposes an endpoint to update MongoDB-stored redirect mappings without proper authorization and input validation, an authenticated or unauthentened attacker (depending on configuration) may inject malicious redirect targets. The combination of a flexible document store, dynamic route handling, and missing output encoding for Location headers increases the likelihood that an otherwise benign configuration feature becomes an abuse vector. Although MongoDB itself does not execute redirects, its data becomes the source of truth for the redirect target in the Restify layer, so insecure handling in the API translates into an exploitable open redirect.

To remediate open redirect issues in Restify when using MongoDB, treat any redirect target sourced from MongoDB as untrusted input. Validate against an allowlist of permitted domains or paths, and prefer internal identifiers that map to pre-approved destinations rather than storing raw external URLs. When constructing a redirect, canonicalize and normalize the target before use, and avoid directly inserting user-controlled strings into the Location header.

Below are concrete code examples for a Restify service that uses MongoDB with safe handling patterns.

const restify = require('restify');
const { MongoClient } = require('mongodb');

const server = restify.createServer();
const allowedRedirectHosts = new Set(['app.example.com', 'static.example.com']);

async function getSafeRedirectUrl(userId, requestedKey) {
  const client = new MongoClient(process.env.MONGODB_URI);
  await client.connect();
  const db = client.db('myapp');
  // Fetch only the field needed; do not trust stored values as-is
  const doc = await db.collection('redirects').findOne({ _id: userId }, { projection: { [requestedKey]: 1 } });
  await client.close();

  if (!doc || !doc[requestedKey]) return null;

  // Canonicalize and validate the stored URL
  const target = new URL(doc[requestedKey]);
  if (!allowedRedirectHosts.has(target.hostname)) {
    return null; // Reject disallowed host
  }
  return target.toString();
}

server.get('/redirect/:userId', async (req, res, next) => {
  const { userId } = req.params;
  const safeUrl = await getSafeRedirectUrl(userId, 'redirectUrl');
  if (!safeUrl) {
    return next(new restify.InvalidArgumentError('Invalid redirect target'));
  }
  res.redirect(302, safeUrl);
  return next();
});

// Alternative: use an internal mapping instead of raw URLs
server.get('/go/:action', async (req, res, next) => {
  const actionMap = {
    dashboard: '/app/dashboard',
    settings: '/app/settings',
    billing: '/app/billing',
  };
  const { action } = req.params;
  if (!actionMap[action]) {
    return next(new restify.InvalidArgumentError('Invalid action'));
  }
  res.redirect(302, actionMap[action]);
  return next();
});

module.exports = server;

Key practices illustrated:

• Use projection to limit retrieved fields and avoid leaking unrelated data.
• Parse the stored URL with the WHATWG URL API to enforce absolute URLs and extract hostname.
• Compare against a strict allowlist of hosts rather than a blocklist.
• Default to internal route mappings when possible to avoid storing external targets in MongoDB.
• Return a clear error via Restify’s InvalidArgumentError when validation fails, avoiding silent fallbacks that could be bypassed.