Nuxt: Unauthorized Component Instantiation via Server Island Props
Impact
Nuxt server islands accept props via the /__nuxt_island/ endpoint. When an application has a server island component that forwards props directly into Vue's dynamic component resolution (<component :is>, resolveDynamicComponent, or h()), an attacker can pass a plain string value (rather than a component definition) to instantiate any globally-registered Vue component or any native HTML element.
For example:
```json
{ "as": "SomeGlobalComponent" }
```
...resolves and renders SomeGlobalComponent if it is globally registered, even though the attacker should only be able to drive props for the island's declared component. Similarly, { "as": "iframe" } renders an <iframe> element.
Unlike the primary RCE vector (GHSA-9473-5f9j-94wq), this does not require vue.runtimeCompiler to be enabled. A plain string prop is sufficient to trigger component resolution. The template/render key guard that addresses the RCE vector does not block plain string values.
Some component libraries expose a polymorphic as / asChild prop that forwards its value into <component :is>; @nuxt/ui (via reka-ui) is a widely used example. An application is affected if such a component receives the attacker-controlled value inside a server island. Note this does not require explicit prop forwarding: island props the island component does not declare fall through as attributes onto its single root element, so an island whose root is a reka-ui / @nuxt/ui component receives the attacker's as value implicitly. Unlike the RCE vector, no vue.runtimeCompiler is required, which makes this vector reachable in more configurations. These libraries are not themselves vulnerable; they are noted only because they commonly provide the dynamic-component sink. Installing @nuxt/ui does not by itself register any component as a server island: the application must define the island (a .server.vue file).
Mitigating factors
- Exploitation requires a server island component that puts an attacker-controlled value onto a dynamic-component path (
<component :is>, resolveDynamicComponent, h(), or a polymorphic as / asChild prop), either explicitly or via attribute fallthrough when the island's root is such a component. - Reachable components are limited to what is actually in the island app's global registry. In a default pages-enabled app that is
RouterView and RouterLink (both registered globally by the pages router plugin, which runs even in component islands), plus any components/global/ component and any component a module registers globally. RouterLink in particular renders an attacker-influenced <a> (and, because an island that declares no props forwards all props, to and other RouterLink props ride the same fallthrough). Vue built-ins (Transition, KeepAlive, Teleport, Suspense) and Nuxt auto-imports (ClientOnly, NuxtLink, NuxtPage, etc.) are NOT in the island app's global registry and cannot be resolved this way; an unresolved name instead renders as a native HTML element (the element-injection half of this issue). - Declaring the props an island accepts, or setting
inheritAttrs: false on it, prevents an undeclared as from falling through to a polymorphic root and neutralizes this vector. - Arbitrary JavaScript execution is not possible through this vector (no
template/render compilation). - Island component names are constrained to the build-time component registry; an attacker cannot resolve arbitrary components.
Affected versions
Nuxt >=3.1.0 <3.21.10 and >=4.0.0 <4.5.1, with component islands active. The island prop-forwarding behavior has existed since server islands were introduced in v3.1.0, and this vector does not depend on vue.runtimeCompiler. Nuxt 2 is not affected.
Note the patch (below) closes the implicit attribute-fallthrough path, which is the majority case. An island that *explicitly* forwards an untrusted prop into dynamic component resolution (or forwards it under a prop name other than as) remains the application's responsibility in every version; see Workarounds.
Patches
Fixed in [email protected] and [email protected]. Patched releases reject a top-level as island prop (HTTP 400 at the /__nuxt_island/ endpoint). This closes the implicit path: island props an island does not declare fall through as attributes onto its single root, so a top-level as would otherwise reach a polymorphic root component's as prop (the reka-ui / @nuxt/ui convention) and drive dynamic component resolution without the author binding it. Rejecting the top-level as prop blocks that fallthrough while leaving nested data and other prop names untouched.
The framework deliberately does not attempt to block every case: it cannot safely tell a string used as data from one used as a component selector, and it has no island-local hook into Vue's h() or `resolveDynamicComponent
