CVE-2026-40864 Details
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.
A vulnerability in JupyterHub versions 4.1.0 prior to 5.4.5 allows cross-site request forgery (XSRF) protection to be bypassed. The issue arises because requests with 'Sec-Fetch-Mode: no-cors' are incorrectly treated as same-origin, leading to a failure in XSRF checks. This vulnerability affects HTTP form endpoints, such as '/hub/spawn' and '/hub/accept-share', but does not impact the JSON API. As a result, an attacker could trigger a server to spawn (without accessing it) or, if they are a JupyterHub user allowed to share their server, cause another user to accept a share and gain access to the attacker's server.
Users can upgrade to JupyterHub version 5.4.5 to address this vulnerability. If a reverse proxy is used, requests to JupyterHub with 'Sec-Fetch-Mode: no-cors' should be dropped.
Metrics
CVSS 4.0 Severity and Vector Strings:
No CVSS 4.0 data is available for this CVE.
CVSS 3.x Severity and Vector Strings:
No data available for CVSS Version 2.0 on this CVE.
CISA-ADP
Assessed May 26, 2026References to Advisories, Solutions, and Tools
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Weakness Enumeration
| CWE-ID | CWE Name | Source |
|---|---|---|
| CWE-352 | Cross-Site Request Forgery (CSRF) | [email protected] |
Affected Products
| Product | Versions |
|---|---|
| jupyter jupyterhub | >= 4.1.0, < 5.4.5 |
CPE
Remediation
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Change History
5 change records found show changes
| Date | Action | Recorded By |
|---|---|---|
| Jul 23, 2026 | CVE Translated | [email protected] |
| Jun 17, 2026 | CVE Modified | [email protected] |
| Jun 17, 2026 | CVE Modified | CISA-ADP |
| Jun 1, 2026 | Initial Analysis | [email protected] |
| May 22, 2026 | New CVE Received | [email protected] |