Package Instance

Cross site scripting (XSS) in JupyterHub via Self-XSS leveraged by Cookie Tossing
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.

JupyterHub is software that allows one to create a multi-user server for Jupyter notebooks. Prior to versions 4.1.6 and 5.1.0, if a user is granted the `admin:users` scope, they may escalate their own privileges by making themselves a full admin user. The impact is relatively small in that `admin:users` is already an extremely privileged scope only granted to trusted users.
In effect, `admin:users` is equivalent to `admin=True`, which is not intended. Note that the change here only prevents escalation to the built-in JupyterHub admin role that has unrestricted permissions. It does not prevent users with e.g. `groups` permissions from granting themselves or other users permissions via group membership, which is intentional. Versions 4.1.6 and 5.1.0 fix this issue.