CVE-2026-45385

### Summary An IDOR vulnerability exists in the Channels feature of `Open WebUI`, allowing any channel member to modify messages sent by other members (including administrators) within the same channel. This vulnerability affects the latest version (`v0.8.12`) of `Open WebUI`. ### Details In the `update_message_by_id` function, for `group` or `dm` type channels, only the caller's membership in the channel is checked via the `is_user_channel_member` function, without verifying message ownership. This allows any channel member to modify messages sent by other members within the same channel. The problematic code is as follows [(https://github.com/open-webui/open-webui/blob/main/backend/open_webui/routers/channels.py#L1355)](https://github.com/open-webui/open-webui/blob/main/backend/open_webui/routers/channels.py#L1355) : ```python if channel.type in ['group', 'dm']: if not Channels.is_user_channel_member(channel.id, user.id, db=db): raise HTTPException(status_code=status.HTTP_403_FORBIDDEN, detail=ERROR_MESSAGES.DEFAULT()) else: if ( user.role != 'admin' and message.user_id != user.id and not channel_has_access(user.id, channel, permission='write', strict=False, db=db) ): raise HTTPException(status_code=status.HTTP_403_FORBIDDEN, detail=ERROR_MESSAGES.DEFAULT()) try: message = Messages.update_message_by_id(message_id, form_data, db=db) ``` Non-group/dm types include a check for the user ID, while the `group/dm` type clearly lacks this verification. ### PoC The `Channels` feature is disabled by default and can be enabled first through the `admin` interface. <img width="1024" height="618" alt="image" src="https://github.com/user-attachments/assets/a36502e9-c6cd-41cd-a69c-8b6ac809768f" /> Create a `group` type channel with members including users `test1` and `test2`. ``` POST /api/v1/channels/create HTTP/1.1 Content-Type: application/json { "name": "idor-test-group", "type": "group", "user_ids": [