Fix Security Misconfiguration in Fastify
Fastify is built for speed, but out-of-the-box defaults are a playground for recon. If you aren't hardening your headers, restricting origins, or scrubbing error stacks, you're handing over the keys to the kingdom. Let's lock it down.
The Vulnerable Pattern
const fastify = require('fastify')({ logger: true });// Missing security headers, permissive CORS, and verbose error leakage fastify.get(‘/data’, async (request, reply) => { try { const data = await performDangerousAction(); return data; } catch (err) { // Dumps full stack trace to client if not handled return err; } });
fastify.listen({ port: 3000 });
The Secure Implementation
Security misconfiguration in Fastify usually stems from three areas: header leakage, permissive CORS, and verbose error messages. We fix this by: 1) Using @fastify/helmet to inject 15+ critical security headers like HSTS, CSP, and X-Frame-Options to mitigate XSS and Clickjacking. 2) Implementing @fastify/cors with a strict whitelist to block unauthorized cross-site requests (CSRF/XS-Leaks). 3) Overriding the default error handler to ensure internal stack traces and database schemas never reach the client, preventing environment fingerprinting. Always ensure AJV validation is active on routes to prevent malformed payload injection.
const fastify = require('fastify')({ logger: true, // Disable 'Server' header to minimize fingerprinting requestIdHeader: false });// 1. Hardened Headers via Helmet fastify.register(require(‘@fastify/helmet’), { contentSecurityPolicy: true, hsts: true });
// 2. Strict CORS Policy fastify.register(require(‘@fastify/cors’), { origin: [‘https://app.secure-domain.com’], methods: [‘GET’, ‘POST’] });
// 3. Global Error Handler to scrub stack traces fastify.setErrorHandler((error, request, reply) => { request.log.error(error); reply.status(500).send({ error: ‘Internal Server Error’, code: ‘SEC_ERR_01’ }); });
fastify.listen({ port: 3000, host: ‘0.0.0.0’ });
Your Fastify API
might be exposed to Security Misconfiguration
74% of Fastify apps fail this check. Hackers use automated scanners to find this specific flaw. Check your codebase before they do.
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