Open WebUI is a self-hosted artificial intelligence platform designed to operate entirely offline. Prior to 0.9.0, the is_user_channel_member function checks whether a ChannelMember row exists but does not check the is_active field. When a user is deactivated from a group or DM channel (removed by the channel owner, or leaves voluntarily), their membership row persists with is_active=False and status='left'. Because the authorization check ignores this field, the deactivated user retains full read and write access to the channel via direct API calls. This vulnerability is fixed in 0.9.0.

Affected: PyPI: open-webui

# Deactivated Channel Members Retain Full Access to Group/DM Channels

## Affected Component

Channel membership authorization check: - `backend/open_webui/models/channels.py` (lines 663-673, `is_user_channel_member`) - Used at 15 locations in `backend/open_webui/routers/channels.py`

## Affected Versions

Current main branch (commit `6fdd19bf1`) and likely all versions with the group/DM channel feature.

## Description

The `is_user_channel_member` function checks whether a `ChannelMember` row exists but does not check the `is_active` field. When a user is deactivated from a group or DM channel (removed by the channel owner, or leaves voluntarily), their membership row persists with `is_active=False` and `status='left'`. Because the authorization check ignores this field, the deactivated user retains full read and write access to the channel via direct API calls.

The channel correctly disappears from the deactivated user's channel list (the listing query at `get_channels_by_user_id` properly filters on `is_active`), but all 15 message-level endpoints in the router rely on `is_user_channel_member` for authorization, which does not filter on `is_active`.

```python # models/channels.py:663 — missing is_active check def is_user_channel_member(self, channel_id, user_id, db=None): membership = db.query(ChannelMember).filter( ChannelMember.channel_id == channel_id, ChannelMember.user_id == user_id, ).first() return membership is not None # True even…

Affected: PyPI: open-webui

# Deactivated Channel Members Retain Full Access to Group/DM Channels

## Affected Component

Channel membership authorization check: - `backend/open_webui/models/channels.py` (lines 663-673, `is_user_channel_member`) - Used at 15 locations in `backend/open_webui/routers/channels.py`

## Affected Versions

Current main branch (commit `6fdd19bf1`) and likely all versions with the group/DM channel feature.

## Description

The `is_user_channel_member` function checks whether a `ChannelMember` row exists but does not check the `is_active` field. When a user is deactivated from a group or DM channel (removed by the channel owner, or leaves voluntarily), their membership row persists with `is_active=False` and `status='left'`. Because the authorization check ignores this field, the deactivated user retains full read and write access to the channel via direct API calls.

The channel correctly disappears from the deactivated user's channel list (the listing query at `get_channels_by_user_id` properly filters on `is_active`), but all 15 message-level endpoints in the router rely on `is_user_channel_member` for authorization, which does not filter on `is_active`.

```python # models/channels.py:663 — missing is_active check def is_user_channel_member(self, channel_id, user_id, db=None): membership = db.query(ChannelMember).filter( ChannelMember.channel_id == channel_id, ChannelMember.user_id == user_id, ).first() return membership is not None # True even…