Vulnerability Description
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.
CVSS Score
MEDIUM
Affected Products
| Vendor | Product | Versions |
|---|---|---|
| Jupyter | Jupyterhub | >= 4.1.0, < 5.4.5 |
Related Weaknesses (CWE)
References
- https://github.com/jupyterhub/jupyterhub/commit/9c5ec277d3cda5a59de2d8c8117efa77Patch
- https://github.com/jupyterhub/jupyterhub/security/advisories/GHSA-m68r-v472-jgq9MitigationVendor Advisory
FAQ
What is CVE-2026-40864?
CVE-2026-40864 is a vulnerability with a CVSS score of 5.4 (MEDIUM). 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 ...
How severe is CVE-2026-40864?
CVE-2026-40864 has been rated MEDIUM with a CVSS base score of 5.4/10. Review the CVSS metrics above for detailed severity breakdown.
Is there a patch for CVE-2026-40864?
Check the references section above for vendor advisories and patch information. Affected products include: Jupyter Jupyterhub.