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.

How to fix CVE-2026-40934

To remediate CVE-2026-40934, upgrade the affected package to a fixed version below.

• —no fix listed
• —upgrade to 2.18.0 or later
• —upgrade to 2.18.0 or later

Is CVE-2026-40934 being exploited?

Low — EPSS is 0.0%, meaning exploitation activity has not been observed at scale.

Affected packages (3)

• from 0
• from 0, < 2.18.0
• from 0, < 2.18.0

CVSS scores

References (5)

• ADVISORYnvd.nist.gov/vuln/detail/CVE-2026-40934
• ADVISORYsecurity-tracker.debian.org/tracker/CVE-2026-40934
• PATCHgithub.com/jupyter-server/jupyter_server
• WEBgithub.com/jupyter-server/jupyter_server/security/advisories/GHSA-5mrq-x3x5-8v8f