Vulnerability Description
Jupyter Server is the backend for Jupyter web applications. In versions 2.17.0 and earlier, the secret used to sign authentication cookies is persisted to a static file at ~/.local/share/jupyter/runtime/jupyter_cookie_secret and is never rotated when a user changes their password. After a password reset and server restart, any previously issued authentication cookie remains cryptographically valid because the signing key has not changed. An attacker who has captured a session cookie through any means retains full authenticated access to the server regardless of subsequent password changes. This affects deployments using password-based authentication, particularly shared or public-facing servers where credential rotation is expected to revoke existing sessions. This issue has been fixed in version 2.18.0.
CVSS Score
MEDIUM
Affected Products
| Vendor | Product | Versions |
|---|---|---|
| Jupyter | Jupyter Server | < 2.18.0 |
Related Weaknesses (CWE)
References
- https://github.com/jupyter-server/jupyter_server/security/advisories/GHSA-5mrq-xExploitVendor AdvisoryMitigation
FAQ
What is CVE-2026-40934?
CVE-2026-40934 is a vulnerability with a CVSS score of 6.8 (MEDIUM). Jupyter Server is the backend for Jupyter web applications. In versions 2.17.0 and earlier, the secret used to sign authentication cookies is persisted to a static file at ~/.local/share/jupyter/runti...
How severe is CVE-2026-40934?
CVE-2026-40934 has been rated MEDIUM with a CVSS base score of 6.8/10. Review the CVSS metrics above for detailed severity breakdown.
Is there a patch for CVE-2026-40934?
Check the references section above for vendor advisories and patch information. Affected products include: Jupyter Jupyter Server.