Read-Only Users Can Modify Collaborative Documents via Socket.IO

Affected Component

Socket.IO collaborative document editing handler:

• backend/open_webui/socket/main.py (lines 667-721, ydoc:document:update handler)

Affected Versions

Current main branch and likely all versions with collaborative note editing.

Description

The ydoc:document:update Socket.IO event handler checks whether the sender is a member of the document's Socket.IO room (line 678) but does not verify that the sender has write permission. Users with read-only access join the document room via ydoc:document:join, which only requires read permission (line 520). Once in the room, the user can emit ydoc:document:update events that modify the in-memory Yjs document state and are broadcast to all other collaborators in real time.

The document_save_handler (line 600) correctly checks write permission before persisting to the database, so the attacker cannot directly save changes. However, the tampered content is visible to all collaborators, and if any user with write access saves the document, the injected content is persisted.

# ydoc:document:update handler (line 667) — only checks room membership, not write permission
async def on_document_update(sid, data):
    document_id = normalize_document_id(data.get('document_id', ''))
    # ...
    room = f'doc_{document_id}'
    if room not in sio.rooms(sid):  # Room membership check only
        return
    # Applies update to Yjs state and broadcasts to all users
    YDOC_MANAGER.apply_update(document_id, update)
    await sio.emit('ydoc:document:update', {...}, room=room, skip_sid=sid)

Compare with ydoc:document:join (line 520) which checks permission:

# Only checks READ permission — so read-only users join the room
if not has_access(user_id, type, id, 'read', db=db):
    return