Nuxt is an open-source web development framework for Vue.js. Starting in version 3.8.1 and prior to version 3.15.3, Nuxt allows any websites to send any requests to the development server and read the response due to default CORS settings. Users with the default server.cors option using Vite builder may get the source code stolen by malicious websites. Version 3.15.3 fixes the vulnerability.

Affected: npm: @nuxt/vite-builder

### Summary Nuxt allows any websites to send any requests to the development server and read the response due to default CORS settings.

### Details While Vite patched the default CORS settings to fix https://github.com/vitejs/vite/security/advisories/GHSA-vg6x-rcgg-rjx6, nuxt uses its own CORS handler by default (https://github.com/nuxt/nuxt/pull/23995).

https://github.com/nuxt/nuxt/blob/7d345c71462d90187fd09c96c7692f306c90def5/packages/vite/src/client.ts#L257-L263

That CORS handler sets `Access-Control-Allow-Origin: *`.

> [!IMPORTANT] > If on an affected version, it may be possible to opt-out of the default Nuxt CORS handler by configuring `vite.server.cors`.

### PoC 1. Start a dev server in any nuxt project using Vite by `nuxt dev`. 2. Send a fetch request to `http://localhost:3000/_nuxt/app.vue` (`fetch('http://localhost:3000/_nuxt/app.vue')`) from a different origin page.

### Impact Users with the default server.cors option using Vite builder may get the source code stolen by malicious websites

### Additional Information `/__nuxt_vite_node__/manifest` / `/__nuxt_vite_node__/module` also seems to have `Access-Control-Allow-Origin: *`, so it maybe also possible to exploit that handler. https://github.com/nuxt/nuxt/blob/7d345c71462d90187fd09c96c7692f306c90def5/packages/vite/src/vite-node.ts#L39 Although I didn't find a valid module id. Note that this handler is probably also vulnerable to DNS rebinding attacks as I didn't find any host header checks.