GHSA-fvcq-4x64-hqxr Jupyter Server Proxy has a reflected XSS issue in host parameter

• PyPI jupyter-server-proxy: >= 3.0.0, < 3.2.4 → fixed in 3.2.4 • PyPI jupyter-server-proxy: >= 4.0.0, < 4.2.0 → fixed in 4.2.0

Impact There is a reflected cross-site scripting (XSS) issue in `jupyter-server-proxy`[1]. The `/proxy` endpoint accepts a `host` path segment in the format `/proxy/`. When this endpoint is called with an invalid `host` value, `jupyter-server-proxy` replies with a response that includes the value of `host`, without sanitization [2]. A third-party actor can leverage this by sending a phishing link with an invalid `host` value containing custom JavaScript to a user. When the user clicks this phishing link, the browser renders the response of `GET /proxy/`, which runs the custom JavaScript contained in `host` set by the actor. As any arbitrary JavaScript can be run after the user clicks on a phishing link, this issue permits extensive access to the user's JupyterLab instance for an actor. This issue exists in the latest release of `jupyter-server-proxy`, currently `v4.1.2`. Impacted versions: `>=3.0.0,<=4.1.2` Patches The patches are included in `==4.2.0` and `==3.2.4`. Workarounds Server operators who are unable to upgrade can disable the `jupyter-server-proxy` extension with: ``` jupyter server extension disable jupyter-server-proxy ``` References [1] : https://github.com/jupyterhub/jupyter-server-proxy/ [2] : https://github.com/jupyterhub/jupyter-server-proxy/blob/62a290f08750f7ae55a0c29ca339c9a39a7b2a7b/jupyter_server_proxy/handlers.py#L328