GitHub Security Advisory: GHSA-vrfh-rj4q-rmhr
Package: open-webui (PIP)
Severity: MODERATE (CVSS 5.4)
CWE: CWE-863: Incorrect Authorization
Vulnerable versions: <= 0.8.12
Patched in: 0.9.0

Summary: Read-Only Open WebUI Users Can Modify Collaborative Documents via Socket.IO

Details:
# 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.

```python
# 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:

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

## CVSS 3.1 Breakdown

| Metric | Value | Rationale |
|--------|-------|-----------|
| Attack Vector | Network (N) | Exploited remotely via Socket.IO events |
| Attack Complexity | Low (L) | No special conditions; attacker emits a standard Socket.IO event |
| Privileges Required | Low (L) | Requires a valid user account with read access to the shared note |
| User Interaction | None (N) | Modifications appear in real time without victim action; however, persistence requires a write-access user to save |
| Scope | Unchanged (U) | Impact is within the collaborative document context |
| Confidentiality | None (N) | No data disclosure beyond what read access already provides |
| Integrity | Low (L) | In-memory document state is modified and broadcast; persistence is indirect (requires another user to save) |
| Availability | Low (L) | Collaborative editing session can be disrupted with invalid content |

## Attack Scenario

1. User A creates a note and shares it with User B with **read** permission.
2. User B opens the note, which triggers `ydoc:document:join` — the server checks read permission a