Cross site scripting (XSS) in JupyterHub via Self-XSS leveraged by Cookie Tossing
ImpactAffected configurations:Single-origin JupyterHub deploymentsJupyterHub deployments with user-controlled applications running on subdomains or peer subdomains of either the Hub or a single-user server.By tricking a user into visiting a malicious subdomain, the attacker can achieve an XSS directly affecting the former's session. More precisely, in the context of JupyterHub, this XSS could achieve the following:Full access to JupyterHub API and user's single-user server, e.g.Create and exfiltrate an API TokenExfiltrate all files hosted on the user's single-user server: notebooks, images, etc.Install malicious extensions. They can be used as a backdoor to silently regain access to victim's session anytime.PatchesTo prevent cookie-tossing:Upgrade to JupyterHub 4.1 (both hub and user environment)enable per-user domains via `c.JupyterHub.subdomain_host = "https://mydomain.example.org"`set `c.JupyterHub.cookie_host_prefix_enabled = True` to enable domain-locked cookiesor, if available (applies to earlier JupyterHub versions):deploy jupyterhub on its own domain, not shared with any other servicesenable per-user domains via `c.JupyterHub.subdomain_host = "https://mydomain.example.org"`