JupyterHub has a privilege escalation vulnerability with the `admin:users` scope

Vulnerability Description

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.

References

• https://github.com/jupyterhub/jupyterhub/security/advisories/GHSA-9x4q-3gxw-849f
• https://github.com/jupyterhub/jupyterhub/commit/99e2720b0fc626cbeeca3c6337f917fdacfaa428
• https://github.com/jupyterhub/jupyterhub/commit/ff2db557a85b6980f90c3158634bf924063ab8ba