Cross-site Scripting via auth_callback login in Home Assistant Core

Summary

Home assistant is an open source home automation. The Home Assistant login page allows users to use their local Home Assistant credentials and log in to another website that specifies the `redirect_uri` and `client_id` parameters. Although the `redirect_uri` validation typically ensures that it matches the `client_id` and the scheme represents either `http` or `https`, Home Assistant will fetch the `client_id` and check for `<link rel="redirect_uri" href="...">` HTML tags on the page. These URLs are not subjected to the same scheme validation and thus allow for arbitrary JavaScript execution on the Home Assistant administration page via usage of `javascript:` scheme URIs. This Cross-site Scripting (XSS) vulnerability can be executed on the Home Assistant frontend domain, which may be used for a full takeover of the Home Assistant account and installation. This issue has been addressed in version 2023.9.0 and all users are advised to upgrade. There are no known workarounds for this vulnerability.