CVE-2026-27898: Vaultwarden has Unauthorized Access via Partial Update API on Another User’s Cipher

In the test environment, it was confirmed that an authenticated regular user can specify another user’s cipher_id and call:

PUT /api/ciphers/{id}/partial

Even though the standard retrieval API correctly denies access to that cipher, the partial update endpoint returns 200 OK and exposes cipherDetails (including name, notes, data, secureNote, etc.).