CVE-2026-54022: Open WebUI: Any authenticated user can read other users' private notes via Socket.IO

The ydoc:document:join Socket.IO handler checks note ownership only when the document_id starts with note: (colon). However, the YdocManager storage layer normalizes all document IDs by replacing colons with underscores (document_id.replace(":", "_")). An attacker can join a document room using note_<id> (underscore) instead of note:<id> (colon), bypassing the authorization check entirely while accessing the same underlying Yjs document. The server then returns the full document state, leaking the victim’s private note contents.