GHSA-7r3h-4ph8-w38g Cross site scripting (XSS) in JupyterHub via Self-XSS leveraged by Cookie Tossing

• PyPI jupyterhub: < 4.1.0 → fixed in 4.1.0

Impact Affected configurations: • Single-origin JupyterHub deployments • JupyterHub 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 Token • Exfiltrate 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. Patches To 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 cookies or, if available (applies to earlier JupyterHub versions): • deploy jupyterhub on its own domain, not shared with any other services • enable per-user domains via `c.JupyterHub.subdomain_host = "https://mydomain.example.org"`