CVE-2026-54338Network attack vectorHinoki check available

Unauthenticated denial of service via unbounded username logging

Published Aug 7, 2026 · Updated Aug 7, 2026

Resource-consumption flaw in JupyterHub before 5.5.0 allows remote attackers to exhaust logging and storage through failed logins. The login handlers and default PAMAuthenticator write the full attacker-controlled username to failed-login logs without a length bound. Only form-based authenticators are exposed; repeated unauthenticated submissions consume log and storage resources, while OAuthenticator deployments are unaffected.

CVSS severity5.3
Medium
EPSS probability0.28%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
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Summary

What happened

Resource-consumption flaw in JupyterHub before 5.5.0 allows remote attackers to exhaust logging and storage through failed logins. The login handlers and default PAMAuthenticator write the full attacker-controlled username to failed-login logs without a length bound. Only form-based authenticators are exposed; repeated unauthenticated submissions consume log and storage resources, while OAuthenticator deployments are unaffected.

The record

CVE
CVE-2026-54338
Published
Aug 7, 2026
Updated
Aug 7, 2026
Vendor
Project Jupyter
Product
JupyterHub
Classifications
CWE-400, T1499.004
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Aug 7, 2026CVE publishedPublication date reported by the CVE source.
  2. Aug 7, 2026Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=< 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.

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Project Jupyter · JupyterHubversion=< 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.

Published CVSS scores

5.3GitHub, Inc.CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

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No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-400Uncontrolled Resource Consumption
T1499.004Application or System Exploitation

Public exploit references

No public exploit references are available in this record.

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Technologies

Your stack

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Your stack

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