---
id: CVE-2026-54338
aliases:
  - GHSA-p43p-whwx-q52h
  - PYSEC-2026-3853
title: >-
  JupyterHub has Unauthenticated Denial of Service via Unbounded Username
  Logging on Failed Login
summary: >-
  JupyterHub has Unauthenticated Denial of Service via Unbounded Username
  Logging on Failed Login
severity: medium
cvss: 5.3
cvssVector: 'CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L'
vendor: jupyterhub
product: jupyterhub
ecosystem: pip
affected:
  - jupyterhub < 5.5.0
patched:
  - jupyterhub 5.5.0
published: '2026-08-25'
updated: '2026-09-10'
sourceUpdated: '2026-09-10T12:25:49.028612030Z'
source: OSV
sourceUrl: 'https://osv.dev/vulnerability/GHSA-p43p-whwx-q52h'
references:
  - url: >-
      https://github.com/jupyterhub/jupyterhub/security/advisories/GHSA-p43p-whwx-q52h
  - url: 'https://nvd.nist.gov/vuln/detail/CVE-2026-54338'
  - url: >-
      https://github.com/jupyterhub/jupyterhub/commit/d6dc595f84b7509969686da31d87d6d69e7fce0a
  - url: 'https://github.com/jupyterhub/jupyterhub'
  - url: 'https://pypi.org/project/jupyterhub'
  - url: 'https://github.com/advisories/GHSA-p43p-whwx-q52h'
tags:
  - osv
  - pip
  - nvd
  - ghsa
epss: 0.00437
epssPercentile: 0.35261
cwe:
  - CWE-400
ingestedAt: '2026-08-25T19:31:03.001Z'
---

## Overview

### Impact

Invalid input to login resulted in unbounded logging output. Only form-based Authenticators (the default PAM Authenticator, but not the more widely used OAuthenticator) are affected.

### Patches

Upgrade to 5.5.0.

### Workarounds

Use an Authenticator that doesn't use a login form, such as OAuthenticator.

## Affected packages

- `jupyterhub < 5.5.0`

## Remediation

Upgrade to a patched release:

- `jupyterhub 5.5.0`