Is CVE-2026-40864 exploited in the wild?

No. Junglewise Threat Intelligence has no report of CVE-2026-40864 being exploited in the wild.

How severe is CVE-2026-40864?

Medium severity, with a CVSS score of 5.4, published 22 May 2026.

Which products and versions are affected?

jupyterhub (PyPI) >= 4.1.0, < 5.4.5, ECOSYSTEM:introduced=4.1.0,fixed=5.4.5.

Is there a fix for CVE-2026-40864?

Yes. jupyterhub (PyPI): upgrade to 5.4.5 or later. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

How is CVE-2026-40864 attacked?

It is attacked over the network, in a software library.

Am I affected by CVE-2026-40864?

Check whether you run jupyterhub (PyPI) at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

CVE-2026-40864: JupyterHub XSRF protection bypass in HTTP form endpoints

Q: Is there a fix for CVE-2026-40864?

Yes. jupyterhub (PyPI): upgrade to 5.4.5 or later. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

Q: How is CVE-2026-40864 attacked?

It is attacked over the network, in a software library.

Q: Am I affected by CVE-2026-40864?

Check whether you run jupyterhub (PyPI) at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

CVE-2026-40864 · Severity: medium · CVSS 5.4 · Published 2026-05-22

JupyterHub, a multi-user platform for Jupyter notebooks, contains a security flaw in its cross-site request forgery (XSRF) protection. An attacker could trick a logged-in user into performing unintended actions, such as starting a server or accepting a shared server connection. While this does not grant the attacker direct access to the user's data, it can be used to manipulate user sessions and server states.

Technologies: jupyterhub (PyPI). Vendors: PyPI.

Quick answers

Is CVE-2026-40864 exploited in the wild?: No. Junglewise Threat Intelligence has no report of CVE-2026-40864 being exploited in the wild.
How severe is CVE-2026-40864?: Medium severity, with a CVSS score of 5.4, published 22 May 2026.
Which products and versions are affected?: jupyterhub (PyPI) >= 4.1.0, < 5.4.5, ECOSYSTEM:introduced=4.1.0,fixed=5.4.5.
Is there a fix for CVE-2026-40864?: Yes. jupyterhub (PyPI): upgrade to 5.4.5 or later. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.
How is CVE-2026-40864 attacked?: It is attacked over the network, in a software library.
Am I affected by CVE-2026-40864?: Check whether you run jupyterhub (PyPI) at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

How to fix

jupyterhub (PyPI): upgrade to 5.4.5 or later
```
pip install "jupyterhub>=5.4.5"
```

Technical details

A Cross-Site Request Forgery (CSRF/XSRF) vulnerability exists in JupyterHub due to an improper implementation of origin checks. The application incorrectly identifies requests containing the 'Sec-Fetch-Mode: no-cors' header as same-origin requests, effectively bypassing XSRF validation for HTTP form endpoints like /hub/spawn and /hub/accept-share. An attacker can exploit this by inducing a victim to submit a cross-origin POST request. This allows the attacker to trigger server spawns or force a user to accept a server share from the attacker. The JSON API is not affected. The issue is resolved in version 5.4.5.

Affected products

jupyterhub jupyterhub >= 4.1.0, < 5.4.5

Identifiers

CVE-2026-40864
GHSA-m68r-v472-jgq9
PYSEC-2026-2189

Timeline

2026-05-05: disclosed
2026-05-05: advisory
2026-05-05: patched

References

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