Is CVE-2026-40934 exploited in the wild?

No. Junglewise Threat Intelligence has no report of CVE-2026-40934 being exploited in the wild.

How severe is CVE-2026-40934?

Medium severity, with a CVSS score of 6.8, published 5 May 2026.

Which products and versions are affected?

Jupyter Server <= 2.17.0; jupyter-server (PyPI) ECOSYSTEM:introduced=0,fixed=2.18.0.

Is there a fix for CVE-2026-40934?

Yes. jupyter-server (PyPI): upgrade to 2.18.0 or later. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

How is CVE-2026-40934 attacked?

It is attacked over the network, in a hosted service.

Am I affected by CVE-2026-40934?

Check whether you run Jupyter Server or jupyter-server (PyPI) at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

CVE-2026-40934: Jupyter Server insufficient session expiration after password reset

Q: Which products and versions are affected?

Jupyter Server <= 2.17.0; jupyter-server (PyPI) ECOSYSTEM:introduced=0,fixed=2.18.0.

Q: Is there a fix for CVE-2026-40934?

Yes. jupyter-server (PyPI): upgrade to 2.18.0 or later. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

Q: How is CVE-2026-40934 attacked?

It is attacked over the network, in a hosted service.

Q: Am I affected by CVE-2026-40934?

Check whether you run Jupyter Server or jupyter-server (PyPI) at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

CVE-2026-40934 · Severity: medium · CVSS 6.8 · Published 2026-05-05

Jupyter Server is a backend application used to run interactive web-based notebooks. A security flaw allows previously issued login sessions to remain valid even after a user changes their password or the server is restarted. This means that if an attacker manages to steal a user's session cookie, they can maintain permanent access to the user's data and environment regardless of any security measures taken to reset credentials.

Technologies: Jupyter Server, jupyter-server (PyPI). Vendors: Jupyter, PyPI.

Quick answers

Is CVE-2026-40934 exploited in the wild?: No. Junglewise Threat Intelligence has no report of CVE-2026-40934 being exploited in the wild.
How severe is CVE-2026-40934?: Medium severity, with a CVSS score of 6.8, published 5 May 2026.
Which products and versions are affected?: Jupyter Server <= 2.17.0; jupyter-server (PyPI) ECOSYSTEM:introduced=0,fixed=2.18.0.
Is there a fix for CVE-2026-40934?: Yes. jupyter-server (PyPI): upgrade to 2.18.0 or later. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.
How is CVE-2026-40934 attacked?: It is attacked over the network, in a hosted service.
Am I affected by CVE-2026-40934?: Check whether you run Jupyter Server or jupyter-server (PyPI) at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

How to fix

jupyter-server (PyPI): upgrade to 2.18.0 or later
```
pip install "jupyter-server>=2.18.0"
```

Technical details

Jupyter Server (versions 2.17.0 and earlier) persists the secret used to sign authentication cookies in a static file located at ~/.local/share/jupyter/runtime/jupyter_cookie_secret. This secret is not rotated when a user changes their password or when the server restarts. Consequently, any session cookie signed with this static key remains cryptographically valid. An attacker who has obtained a session cookie (via XSS, local access, or other means) can maintain authenticated access to the server indefinitely, bypassing password-based revocation. The issue is classified as CWE-613 (Insufficient Session Expiration) and is fixed in version 2.18.0.

Affected products

Jupyter Jupyter Server <= 2.17.0

Identifiers

CVE-2026-40934
GHSA-5mrq-x3x5-8v8f
PYSEC-2026-69

Timeline

2026-05-05: advisory: GitHub Advisory GHSA-5mrq-x3x5-8v8f published
2026-05-05: disclosed
2026-05-05: patched: Fixed in version 2.18.0

References

https://github.com/jupyter-server/jupyter_server/security/advisories/GHSA-5mrq-x3x5-8v8f

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