Fix Security Misconfiguration in ElysiaJS

ElysiaJS is high-performance, but speed often masks critical security oversights. Out-of-the-box, it lacks essential security headers, employs overly permissive CORS, and leaks sensitive stack traces during failures. To harden an Elysia instance, you must move beyond the 'everything-is-allowed' default state and implement a defense-in-depth strategy using middleware and explicit error handling.

The Vulnerable Pattern

import { Elysia } from 'elysia';
// VULNERABLE: Default configuration lacks headers and leaks info
const app = new Elysia()
.get(‘/user/:id’, ({ params }) => {
// Potential Information Disclosure via unhandled errors
if (params.id === ‘admin’) throw new Error(‘DB_CONN_STRING: postgres://admin:password123@localhost:5432’);
return { user: params.id };
})
.listen(3000);

The Secure Implementation

The vulnerable code suffers from three major misconfigurations: 1. Lack of CORS policy allows any malicious site to perform cross-origin requests. 2. Missing Security Headers (Helmet) makes the app susceptible to XSS, Sniffing, and Clickjacking. 3. Verbose Error Handling leaks internal environment variables and database strings to the client. The secure implementation mitigates this by: using the @elysiajs/cors plugin to whitelist origins, utilizing Helmet to set restrictive HTTP headers, and implementing a global .error() handler to ensure stack traces and internal logic never reach the end-user.

import { Elysia } from 'elysia';
import { cors } from ‘@elysiajs/cors’;
import { helmet } from ‘elysia-helmet’;
const app = new Elysia()
// 1. Lockdown CORS to specific origins
.use(cors({
origin: ‘https://app.production.com’,
methods: [‘GET’, ‘POST’]
}))
// 2. Inject security headers (CSP, HSTS, X-Frame-Options)
.use(helmet())
// 3. Global Error Handling to prevent Information Disclosure
.error(({ code, error, set }) => {
console.error([SEC-LOG] ${code}: ${error.message}); // Log internally
set.status = 500;
return { status: ‘error’, message: ‘Internal Server Error’ }; // Masked response
})
.get(‘/user/:id’, ({ params }) => {
return { user: params.id };
})
.listen(3000);