Nuxt's route middleware is not enforced when rendering `.server.vue` pages via `/__nuxt_island/page_*`

Summary

When experimental.componentIslands is enabled (default in Nuxt 4), any .server.vue file under pages/ is automatically registered as a server island under the key page_<routeName> and exposed via the /__nuxt_island/:name endpoint. Until this fix, requests through that endpoint rendered the page component directly via the SSR renderer without instantiating Vue Router, which meant route middleware declared on the page (including definePageMeta({ middleware })) did not run.

For Nuxt applications that gate a .server.vue page behind route middleware as their sole auth check, an unauthenticated attacker could bypass that check by requesting /__nuxt_island/page_<routeName>_<anyhash> directly and receiving the server-rendered HTML.

Affected configurations

All three conditions must hold for an application to be vulnerable:

1. experimental.componentIslands is enabled (the default in Nuxt 4; opt-in in Nuxt 3).
2. The application defines one or more .server.vue files under pages/, registering them as routed pages.
3. Authentication / authorization for at least one such page is enforced solely via route middleware (middleware/*.ts referenced from definePageMeta), without a server-side check inside the page or its data layer.

Applications that enforce auth inside the island's own data layer (server-only API routes, useRequestEvent + manual session checks, etc.) were not affected. The general "route middleware does not run for non-page island components" behaviour is documented and unchanged; this advisory concerns the .server.vue page case specifically, where running middleware is the user's clear expectation.

Details

• Build (packages/nuxt/src/components/templates.ts): .server.vue pages are registered as island components with page_ prefix, making them addressable through /__nuxt_island/page_<routeName>_<hashId>.
• Runtime (packages/nitro-server/src/runtime/handlers/island.ts): the handler resolves the requested island component and renders it via renderer.renderToString(ssrContext). The Vue Router plugin previously short-circuited middleware execution whenever ssrContext.islandContext was set.
• The two paths interact so that route middleware declared on the source page never runs.

Proof of concept

Given a page app/pages/secret.server.vue:

<script setup lang="ts">
definePageMeta({ middleware: 'auth' })
</script>

<template>
<h1>SECRET DATA</h1>
</template>

with middleware/auth.ts blocking unauthenticated access:

# Direct page request: blocked by middleware
curl -i http://localhost:3000/secret
# -> 403 / redirect, depending on the middleware

# Island request: middleware did not run before this fix
curl -i 'http://localhost:3000/__nuxt_island/page_secret_anyhash'
# -> 200 OK, body includes <h1>SECRET DATA</h1>

Patches

Patched in nuxt@4.4.6 and nuxt@3.21.6 by #35092. The Vue Router plugin now runs middleware and redirect handling for page_* islands (i.e. islands that originate from .server.vue files in pages/). The island handler propagates middleware-issued responses (~renderResponse), and a new beforeResolve guard returns HTTP 400 when the requested page_<name> does not match the route component the URL resolves to.

Non-page island components are unaffected - they continue to render without route middleware, by design.

Workarounds

If you cannot upgrade immediately:

• Enforce authentication inside the .server.vue page itself, not via route middleware. Read the session from useRequestEvent() and throw createError({ statusCode: 401 }) (or redirect) before returning data. This is the recommended pattern for islands regardless of this advisory.
• Disable experimental.componentIslands if your app does not use the feature.
• If your app must keep route-middleware-only auth, gate the /__nuxt_island/page_* URL prefix at your reverse proxy or in a server middleware.