---
id: CVE-2021-41194
aliases:
  - GHSA-5xvc-vgmp-jgc3
  - PYSEC-2021-384
title: Improper Access Control in jupyterhub-firstuseauthenticator
summary: Improper Access Control in jupyterhub-firstuseauthenticator
severity: critical
cvss: 9.1
cvssVector: 'CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N'
vendor: jupyterhub-firstuseauthenticator
product: jupyterhub-firstuseauthenticator
ecosystem: pip
affected:
  - jupyterhub-firstuseauthenticator < 1.0.0
patched:
  - jupyterhub-firstuseauthenticator 1.0.0
published: '2021-10-28'
updated: '2026-07-08'
source: OSV
sourceUrl: 'https://osv.dev/vulnerability/GHSA-5xvc-vgmp-jgc3'
references:
  - url: >-
      https://github.com/jupyterhub/firstuseauthenticator/security/advisories/GHSA-5xvc-vgmp-jgc3
  - url: 'https://nvd.nist.gov/vuln/detail/CVE-2021-41194'
  - url: 'https://github.com/jupyterhub/firstuseauthenticator/pull/38'
  - url: 'https://github.com/jupyterhub/firstuseauthenticator/pull/38.patch'
  - url: >-
      https://github.com/jupyterhub/firstuseauthenticator/pull/38/commits/32b21898fb2b53b1a2e36270de6854ad70e9e9bf
  - url: >-
      https://github.com/jupyterhub/firstuseauthenticator/pull/38/commits/9e200d974e0cb85d828a6afedb8ab90a37878f28
  - url: >-
      https://github.com/jupyterhub/firstuseauthenticator/commit/953418e2450dbc2d854e332350849533b0ebc7ba
  - url: 'https://github.com/jupyterhub/firstuseauthenticator'
  - url: >-
      https://github.com/pypa/advisory-database/tree/main/vulns/jupyterhub-firstuseauthenticator/PYSEC-2021-384.yaml
tags:
  - osv
  - pip
epss: 0.01367
epssPercentile: 0.70647
ingestedAt: '2026-07-08T18:25:46.252Z'
---

## Overview

### Impact

When JupyterHub is used with FirstUseAuthenticator, the vulnerability allows unauthorized access to any user's account if `create_users=True` and the username is known or guessed.

### Patches

Upgrade to jupyterhub-firstuseauthenticator to 1.0, or apply patch https://github.com/jupyterhub/firstuseauthenticator/pull/38.patch

### Workarounds

If you cannot upgrade, there is no complete workaround, but it can be mitigated.

If you cannot upgrade yet, you 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. If any users have never logged in with their normalized username (i.e. lowercase), they will still be vulnerable until you can patch or upgrade.

## Affected packages

- `jupyterhub-firstuseauthenticator < 1.0.0`

## Remediation

Upgrade to a patched release:

- `jupyterhub-firstuseauthenticator 1.0.0`