CVE-2020-26250 Base class whitelist configuration ignored in OAuthenticator

What is CVE-2020-26250?

CVE-2020-26250 is a medium-severity missing authorization vulnerability in jupyterhub oauthenticator, published on 1 Dec 2020. Any signed-in user can exploit it over the network, with no action from the victim.

Official description

OAuthenticator is an OAuth login mechanism for JupyterHub. In oauthenticator from version 0.12.0 and before 0.12.2, the deprecated (in jupyterhub 1.2) configuration `Authenticator.whitelist`, which should be transparently mapped to `Authenticator.allowed_users` with a warning, is instead ignored by OAuthenticator classes, resulting in the same behavior as if this configuration has not been set. If this is the only mechanism of authorization restriction (i.e. no group or team restrictions in configuration) then all authenticated users will be allowed. Provider-based restrictions, including deprecated values such as `GitHubOAuthenticator.org_whitelist` are **not** affected. All users of OAuthenticator 0.12.0 and 0.12.1 with JupyterHub 1.2 (JupyterHub Helm chart 0.10.0-0.10.5) who use the `admin.whitelist.users` configuration in the jupyterhub helm chart or the `c.Authenticator.whitelist` configuration directly. Users of other deprecated configuration, e.g. `c.GitHubOAuthenticator.team_whitelist` are **not** affected. If you see a log line like this and expect a specific list of allowed usernames: "[I 2020-11-27 16:51:54.528 JupyterHub app:1717] Not using allowed_users. Any authenticated user will be allowed." you are likely affected. Updating oauthenticator to 0.12.2 is recommended. A workaround is to replace the deprecated `c.Authenticator.whitelist = ...` with `c.Authenticator.allowed_users = ...`. If any users have been authorized during this time who should not have been, they must be deleted via the API or admin interface, per the referenced documentation.

Weakness: CWE-863

Which versions are affected by CVE-2020-26250?

3 open source packages ship an affected version, including oauthenticator. It affects 1 product.

Products include Jupyter Oauthenticator.

How do I fix CVE-2020-26250?

Upgrade oauthenticator to 0.12.2 or later.

Upgrade, and check permissions on every request on the server, not only in the interface. More about Missing authorization.

Is CVE-2020-26250 being exploited?

There is no known exploitation of CVE-2020-26250 in the wild and no public exploit code.

Other vulnerabilities in jupyterhub oauthenticator

• CVE-2026-33175 OAuthenticator: Authentication Bypass in Auth0OAuthenticator via Unverified Email Claims High 8.8
• CVE-2018-7206 JupyterHub OAuthenticator elevation of privilege High 8.8
• CVE-2024-29033 GoogleOAuthenticator.hosted_domain incorrectly verifies membership of an Google organization/workspace High 7.5
• CVE-2022-31027 Authorization Bypass Through User-Controlled Key when using CILogonOAuthenticator in oauthenticator Medium 4.2

Sources

• CVE record
• NVD
• OSV
• GitHub advisory
• How this page is made

Also known as GHSA-384w-5v3f-q499, PYSEC-2020-68.