Vulnerability · Published Aug 7, 2026 · Assigned by GitHub_M
CVE-2026-54338JupyterHub: Unauthenticated Denial of Service via Unbounded Username Logging on Failed Login
Medium 5.3
In plain English
A medium-severity uncontrolled resource consumption in jupyterhub from jupyterhub. There are no confirmed reports of exploitation so far. The chance it is exploited in the next 30 days is estimated at 0.4% (higher than 38% of all known vulnerabilities). Fixed versions are available - upgrade the affected package.
Official description
JupyterHub is software that allows users to create a multi-user server for Jupyter notebooks. Prior to 5.5.0, invalid input to form-based login authenticators can place an unbounded attacker-controlled username in failed-login logs, allowing an unauthenticated attacker to consume logging and storage resources. This issue is fixed in version 5.5.0.
Affected packages & fixed versions
| Ecosystem | Package | Fixed in | Advisory |
|---|---|---|---|
| Debian:12 | jupyterhub | no fix listed | DEBIAN-CVE-2026-54338 |
| Debian:13 | jupyterhub | no fix listed | DEBIAN-CVE-2026-54338 |
| Debian:14 | jupyterhub | no fix listed | DEBIAN-CVE-2026-54338 |
| PyPI | jupyterhub | 5.5.0 | GHSA-p43p-whwx-q52h |
| PyPI | jupyterhub | 5.5.0 | PYSEC-2026-3853 |
| Ubuntu:22.04:LTS | jupyterhub | no fix listed | UBUNTU-CVE-2026-54338 |
| Ubuntu:24.04:LTS | jupyterhub | no fix listed | UBUNTU-CVE-2026-54338 |
| Ubuntu:26.04:LTS | jupyterhub | no fix listed | UBUNTU-CVE-2026-54338 |
| Ubuntu:26.10 | jupyterhub | no fix listed | UBUNTU-CVE-2026-54338 |
Affected products (as reported)
| Vendor | Product | Versions |
|---|---|---|
| jupyterhub | jupyterhub | < 5.5.0JupyterHub is software that allows users to create a multi-user server for Jupyter notebooks. Prior to 5.5.0, invalid input to form-based login authenticators can place an unbounded attacker-controlled username in failed-login logs, allowing an unauthenticated attacker to consume logging and storage resources. This issue is fixed in version 5.5.0. |
Weakness: CWE-400 · Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L