jupyterhub up to 5.4.4 JSON API /hub/spawn cross-site request forgery

Summaryinfo

A vulnerability has been found in jupyterhub up to 5.4.4 and classified as problematic. Affected by this vulnerability is an unknown functionality of the file /hub/spawn of the component JSON API. Performing a manipulation results in cross-site request forgery. This vulnerability is reported as CVE-2026-40864. The attack is possible to be carried out remotely. No exploit exists. The affected component should be upgraded.

Detailsinfo

A vulnerability, which was classified as problematic, was found in jupyterhub up to 5.4.4. This affects an unknown part of the file /hub/spawn of the component JSON API. The manipulation with an unknown input leads to a cross-site request forgery vulnerability. CWE is classifying the issue as CWE-352. The web application does not, or can not, sufficiently verify whether a well-formed, valid, consistent request was intentionally provided by the user who submitted the request. This is going to have an impact on integrity. The summary by CVE is:

JupyterHub is software that allows users to create a multi-user server for Jupyter notebooks. In versions 4.1.0 through 5.4.4, XSRF protection (updated in 4.1.0) inappropriately treated requests with Sec-Fetch-Mode: no-cors as same-origin requests, bypassing XSRF checks. The JSON API is not affected, only HTTP form endpoints, such as /hub/spawn and /hub/accept-share, meaning attackers could trigger server spawn (but not access the server) and if the attacker is a JupyterHub user permitted to share access to their server, cause a user to accept a share and have access to the attacker's server. This issue has been fixed in version 5.4.5. If developers are unable to immediately upgrade, they can temporarily mitigate this issue by dropping requests to JupyterHub with Sec-Fetch-Mode: no-cors if they are using a reverse proxy.

The advisory is shared at github.com. This vulnerability is uniquely identified as CVE-2026-40864 since 04/15/2026. The exploitability is told to be easy. It is possible to initiate the attack remotely. No form of authentication is needed for exploitation. It demands that the victim is doing some kind of user interaction. Technical details are known, but no exploit is available.

The vulnerability scanner Nessus provides a plugin with the ID 316606 (Linux Distros Unpatched Vulnerability : CVE-2026-40864), which helps to determine the existence of the flaw in a target environment.

Upgrading to version 5.4.5 eliminates this vulnerability. Applying the patch 9c5ec277d3cda5a59de2d8c8117efa77bd941127 is able to eliminate this problem. The bugfix is ready for download at github.com. The best possible mitigation is suggested to be upgrading to the latest version.

The vulnerability is also documented in the vulnerability database at Tenable (316606). If you want to get the best quality for vulnerability data then you always have to consider VulDB.

Productinfo

Name

• jupyterhub

Version

• 5.4.0
• 5.4.1
• 5.4.2
• 5.4.3
• 5.4.4

License

• open-source

Website

• Product: https://github.com/jupyterhub/jupyterhub/

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If you want to get the best quality for vulnerability data then you always have to consider VulDB.

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