Nuxt is an open-source web development framework for Vue.js. From 3.13.0 until 4.6.2, the server-island renderer serializes raw useHeadSafe entry input into the island response without preserving the safe-input marker, and NuxtIsland later inserts that input into the page head as an ordinary entry. An application that passes attacker-controlled data to useHeadSafe in a .server.vue component or page, or in a component rendered through NuxtIsland, can therefore render values normally removed by the allowlist, including event-handler attributes or executable script content, resulting in stored cross-site scripting in the application origin. This issue is fixed in version 4.6.2 .

Affected: npm: nuxt

## Impact

`useHeadSafe` restricts head input to an allowlist of safe tags and attributes. For example, `bodyAttrs` is limited to `class` and `style`, event handler attributes are removed, and `<script>` tags are only kept for JSON types.

When `useHeadSafe` is called inside a server island (a `.server.vue` component or page, or a component rendered with `<NuxtIsland>`), the island renderer serialises the raw input of every head entry into the island response without the option that marks it as safe input. `<NuxtIsland>` then pushes that input into the page's head as a regular entry, both during server rendering and when hydrating or refetching on the client.

As a result, input that `useHeadSafe` would normally strip (such as `bodyAttrs.onload` or executable `<script>` content) is rendered into the page. If an application passes user-controlled data to `useHeadSafe` inside a server island, an attacker who controls that data can achieve stored cross-site scripting on the application's origin.

```vue <!-- components/AuthorMeta.server.vue --> <script setup lang="ts"> const { data: author } = await useFetch('/api/author') // author.value.head is user-authored, e.g. { bodyAttrs: { onload: '...' } } useHeadSafe(author.value.head) </script> ```

## Mitigating factors

- Server components are experimental. They are only active when the application defines a `.server.vue` component or page, or enables `experimental.componentIslands` and renders `<NuxtIsland>`. - Exploitation requir…