Nuxt has Client-Side Path Traversal in Nuxt Island Payload Revival

Summary

A client-side path traversal vulnerability in Nuxt's Island payload revival mechanism allowed attackers to manipulate client-side requests to different endpoints within the same application domain when specific prerendering conditions are met.

Technical Details

The vulnerability occurs in the client-side payload revival process (revive-payload.client.ts) where Nuxt Islands are automatically fetched when encountering serialized __nuxt_island objects. The issue affects the following flow:

1. During prerendering, if an API endpoint returns user-controlled data containing a crafted __nuxt_island object
2. This data gets serialized with devalue.stringify and stored in the prerendered page
3. When a client navigates to the prerendered page, devalue.parse deserializes the payload
4. The Island reviver attempts to fetch /__nuxt_island/${key}.json where key could contain path traversal sequences

Prerequisites for Exploitation

This vulnerability requires all of the following conditions:

1. Prerendered pages: The application must use Nuxt's prerendering feature (nitro.prerender)
2. Attacker-controlled API responses: The attacker must be able to control the response content of an API endpoint that is called during prerendering via useFetch, useAsyncData, or similar composables
3. Client-side navigation: A user must navigate to the prerendered page (not during initial SSR hydration)

Attack Scenario

// Malicious API response during prerendering
{
  "__nuxt_island": {
    "key": "../../../../internal/service",
    "params": { "action": "probe" }
  }
}

This could cause the client to make requests to /__nuxt_island/../../../../internal/service.json if path traversal is not properly handled by the server.

Impact Assessment

• Limited Impact: The vulnerability has a low severity due to the highly specific prerequisites
• No Direct Data Exfiltration: The vulnerability does not directly expose sensitive data
• Client-Side Only: Requests originate from the client, not the server

Mitigation

Action Required:

• Update to Nuxt 3.19.0+ or 4.1.0+ immediately