CVE-2026-40934

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.

Predictions

Heuristic predictions, AS-IS, for prioritization only.

Mitigations

References

• https://github.com/jupyter-server/jupyter_server/security/advisories/GHSA-5mrq-x3x5-8v8f
• https://nvd.nist.gov/vuln/detail/CVE-2026-40934
• https://github.com/jupyter-server/jupyter_server
• https://security-tracker.debian.org/tracker/CVE-2026-40934
• https://github.com/advisories/GHSA-5mrq-x3x5-8v8f

CWEs

CWE-613