CVE-2026-54338

JupyterHub: Unauthenticated Denial of Service via Unbounded Username Logging on Failed Login

State: Published
Severity: 5.3 Medium
Published: Aug 7, 2026
Updated: Aug 11, 2026
Reserved: Jun 12, 2026

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.

Scores

CVSS	Score	Vector	Source
3.1	5.3 Medium	CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L	GitHub_M

Weaknesses

CWE-400 Uncontrolled Resource Consumption

Affected Products

Product	Versions
jupyterhubjupyterhub	< 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.Affected

References

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