Open WebUI has an IDOR vulnerability in the pin_channel_message API endpoint

Summary

Pin/Unpin is a write operation (modifies the message's is_pinned , pinned_by, pinned_at fields), but in standard channels it only checks read permission, allowing users with read-only access to pin/unpin any message.

Details

https://github.com/open-webui/open-webui/blob/9bd84258d09eefe7bf975878fb0e31a5dadfe0f8/backend/open_webui/routers/channels.py#L1218

@router.post('/{id}/messages/{message_id}/pin', response_model=Optional[MessageUserResponse])
async def pin_channel_message(
    request: Request,
    id: str,
    message_id: str,
    form_data: PinMessageForm,
    user=Depends(get_verified_user),
    db: Session = Depends(get_session),
):
    check_channels_access(request)
    channel = Channels.get_channel_by_id(id, db=db)
    if not channel:
        raise HTTPException(status_code=status.HTTP_404_NOT_FOUND, detail=ERROR_MESSAGES.NOT_FOUND)

    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 not channel_has_access(user.id, channel, permission='read', db=db):
            raise HTTPException(status_code=status.HTTP_403_FORBIDDEN, detail=ERROR_MESSAGES.DEFAULT())

The channel_has_access function https://github.com/open-webui/open-webui/blob/9bd84258d09eefe7bf975878fb0e31a5dadfe0f8/backend/open_webui/routers/channels.py#L75 checks user permissions against the AccessGrants table:

def channel_has_access(
    user_id: str,
    channel: ChannelModel,
    permission: str = 'read',  # 'read' or 'write'
    strict: bool = True,
    db: Optional[Session] = None,
) -> bool:
    if AccessGrants.has_access(
        user_id=user_id,
        resource_type='channel',
        resource_id=channel.id,
        permission=permission,
        db=db,
    ):
        return True
    # ...

The AccessGrant table distinguishes between read and write permission levels.

PoC

admin creates Standard Channel with Read-Only Access for test1 :

POST /api/v1/channels/create
Authorization: 
Content-Type: application/json

{
  "name": "pin-test-standard",
  "access_grants": [
    {
      "principal_type": "user",
      "principal_id": "cfc3cb19-9e92-4bf7-8b72-1b47fe4ff62c",
      "permission": "read"
    }
  ]
}