CVE-2026-40864Public exploitNetwork attack vector

Cross-site request forgery via no-cors misclassification

Published May 22, 2026 · Updated May 22, 2026

Cross-site request forgery in Project Jupyter JupyterHub 4.1.0 through 5.4.4 allows remote attackers to submit cross-origin form actions. The _needs_check_xsrf function in jupyterhub/_xsrf_utils.py treats Sec-Fetch-Mode: no-cors as trusted and skips token validation for HTTP form endpoints. A victim must be signed in and visit attacker-controlled content; the forged request can spawn a server without granting access, or accept a share when the attacker is permitted to share.

CVSS severity5.4
Medium
EPSS probability0.16%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Cross-site request forgery in Project Jupyter JupyterHub 4.1.0 through 5.4.4 allows remote attackers to submit cross-origin form actions. The _needs_check_xsrf function in jupyterhub/_xsrf_utils.py treats Sec-Fetch-Mode: no-cors as trusted and skips token validation for HTTP form endpoints. A victim must be signed in and visit attacker-controlled content; the forged request can spawn a server without granting access, or accept a share when the attacker is permitted to share.

The record

CVE
CVE-2026-40864
Published
May 22, 2026
Updated
May 22, 2026
Vendor
Project Jupyter
Product
JupyterHub
Classifications
CWE-352, T1204.001
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. May 22, 2026CVE publishedPublication date reported by the CVE source.
  2. May 22, 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=>= 4.1.0, < 5.4.5

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Project Jupyter · JupyterHubversion=>= 4.1.0, < 5.4.5

Published CVSS scores

4.3NIST NVDCVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:L/A:N
5.4GitHubCVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:L/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.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

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 exploitPublished

Weakness, pattern, technique

CWE-352Cross-Site Request Forgery (CSRF)
T1204.001Malicious Link

Public exploit references

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

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Your stack

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