{"id":"CVE-2021-41194","aliases":["GHSA-5xvc-vgmp-jgc3","PYSEC-2021-384"],"url":"https://o3.security/vulnerability/CVE-2021-41194","summary":"Improper Access Control in jupyterhub-firstuseauthenticator","details":"FirstUseAuthenticator is a JupyterHub authenticator that helps new users set their password on their first login to JupyterHub. When JupyterHub is used with FirstUseAuthenticator, a vulnerability in versions prior to 1.0.0 allows unauthorized access to any user's account if `create_users=True` and the username is known or guessed. One may upgrade to version 1.0.0 or apply a patch manually to mitigate the vulnerability. For those who cannot upgrade, there is no complete workaround, but a partial mitigation exists. One can disable user creation with `c.FirstUseAuthenticator.create_users = False`, which will only allow login with fully normalized usernames for already existing users prior to jupyterhub-firstuserauthenticator 1.0.0. If any users have never logged in with their normalized username (i.e. lowercase), they will still be vulnerable until a patch or upgrade occurs.","published":"2021-10-28T20:15:07.680Z","modified":"2026-07-09T12:20:38.636750Z","cvss":{"score":9.8,"severity":"CRITICAL","vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H"},"epss":{"score":0.01367,"percentile":0.69349,"asOf":"2026-08-23"},"cisaKev":null,"exploitsKnown":0,"affectedPackages":[{"ecosystem":"PyPI","name":"jupyterhub-firstuseauthenticator","fixedVersion":"1.0.0"}],"fix":{"url":"https://github.com/jupyterhub/firstuseauthenticator/pull/38","label":"jupyterhub/firstuseauthenticator#38"},"references":[{"type":"ADVISORY","url":"https://github.com/jupyterhub/firstuseauthenticator/security/advisories/GHSA-5xvc-vgmp-jgc3"},{"type":"FIX","url":"https://github.com/jupyterhub/firstuseauthenticator/pull/38"},{"type":"FIX","url":"https://github.com/jupyterhub/firstuseauthenticator/pull/38.patch"}],"provenance":{"sources":["OSV.dev","FIRST.org (EPSS)"],"lastVerified":"2026-07-09T12:20:38.636750Z"}}