Nuxt server islands render `useHeadSafe` input without sanitisation

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.

<!-- 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 requires the application to pass attacker-controlled data to useHeadSafe inside a server island. useHeadSafe called from regular (non-island) components and pages is not affected.

Affected versions

nuxt >=3.13.0, when head support for server islands was introduced. Nuxt 2 is not affected.

Patches

Fixed in [email protected]. Nuxt 3 reached end of life on 31 July 2026 and will not receive a fix.

Patched releases apply Unhead's safe input filtering to useHeadSafe entries on the server before they are added to the island response, so islandResponse.head (including what render:island hooks see) only contains input that useHeadSafe allows.

Workarounds

Upgrade to [email protected]. If you cannot upgrade, including on Nuxt 3:

1. Call useHeadSafe with untrusted input from a regular component or page rather than from inside a server island.
2. Alternatively, validate untrusted head input against your own allowlist before passing it to useHeadSafe inside a server island.