GoogleOAuthenticator.hosted_domain incorrectly verifies membership of an Google organization/workspace

Summary and impact

GoogleOAuthenticator.hosted_domain is used to restrict what Google accounts can be authorized to access a JupyterHub. The restriction is intended to ensure Google accounts are part of one or more Google organizations/workspaces verified to control specified domain(s).

The vulnerability is that the actual restriction has been to Google accounts with emails ending with the domain. Such accounts could have been created by anyone which at one time was able to read an email associated with the domain. This was described by Dylan Ayrey (@dxa4481) in this blog post from 15th December 2023.

Remediation

Upgrade to oauthenticator>=16.3.0 or restrict who can login another way, such as allowed_users or allowed_google_groups.