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

Moderate severity GitHub Reviewed Published Jul 18, 2026 in jupyterhub/jupyterhub

Package

pip jupyterhub (pip)

Affected versions

< 5.5.0

Patched versions

5.5.0

Description

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.

References

@minrk minrk published to jupyterhub/jupyterhub Jul 18, 2026
Published by the National Vulnerability Database Aug 7, 2026
Published to the GitHub Advisory Database Aug 25, 2026
Reviewed Aug 25, 2026

Severity

Moderate

CVSS overall score

This score calculates overall vulnerability severity from 0 to 10 and is based on the Common Vulnerability Scoring System (CVSS).
/ 10

CVSS v3 base metrics

Attack vector
Network
Attack complexity
Low
Privileges required
None
User interaction
None
Scope
Unchanged
Confidentiality
None
Integrity
None
Availability
Low

CVSS v3 base metrics

Attack vector: More severe the more the remote (logically and physically) an attacker can be in order to exploit the vulnerability.
Attack complexity: More severe for the least complex attacks.
Privileges required: More severe if no privileges are required.
User interaction: More severe when no user interaction is required.
Scope: More severe when a scope change occurs, e.g. one vulnerable component impacts resources in components beyond its security scope.
Confidentiality: More severe when loss of data confidentiality is highest, measuring the level of data access available to an unauthorized user.
Integrity: More severe when loss of data integrity is the highest, measuring the consequence of data modification possible by an unauthorized user.
Availability: More severe when the loss of impacted component availability is highest.
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L

EPSS score

Exploit Prediction Scoring System (EPSS)

This score estimates the probability of this vulnerability being exploited within the next 30 days. Data provided by FIRST.
(20th percentile)

Weaknesses

Uncontrolled Resource Consumption

The product does not properly control the allocation and maintenance of a limited resource. Learn more on MITRE.

CVE ID

CVE-2026-54338

GHSA ID

GHSA-p43p-whwx-q52h

Source code

Credits

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