How severe is CVE-2026-40934?

No CVSS score has been assigned to CVE-2026-40934 yet. Review the advisory details and affected package list to assess your exposure.

Which packages are affected by CVE-2026-40934?

CVE-2026-40934 affects the following packages: jupyter-server (PyPI). Ecosystems affected: PyPI.

How do I fix CVE-2026-40934?

Update jupyter-server to 2.18.0 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-40934 is resolved across your whole dependency graph.

How do I detect CVE-2026-40934 in my PyPI dependencies?

Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for jupyter-server, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.

How do I mitigate CVE-2026-40934 if there is no patch (or I can't update yet)?

Put an independent control in front of the weakness: restrict the affected endpoint or interface to trusted networks, require an additional authentication factor or proxy-level check, and invalidate existing sessions and credentials in case the flaw has already been used.

Is CVE-2026-40934 actively exploited in the wild?

No public exploit code has been indexed for CVE-2026-40934 yet. This does not mean the vulnerability cannot be exploited — absence of public exploits does not imply safety. Apply the recommended fix and use O3 Security to monitor your exposure.

What is the EPSS score for CVE-2026-40934?

CVE-2026-40934 has an EPSS (Exploit Prediction Scoring System) score of 0.3%, placing it in the 27th percentile of all CVEs. EPSS is maintained by FIRST.org and estimates the probability that a vulnerability will be exploited in the wild within the next 30 days. This score indicates relatively lower exploitation probability, though the CVSS severity should still guide your patching priority.

What type of vulnerability is CVE-2026-40934?

CVE-2026-40934 is classified as CWE-613 (CWE-613). This weakness type describe the underlying flaw category, which helps determine the potential impact and the right class of mitigation.

When was CVE-2026-40934 published, and has it been updated?

CVE-2026-40934 was published on May 5, 2026 and was last updated on October 28, 2026. Advisory data evolves as severity scores, affected ranges, and exploit intelligence are revised — always check the latest version of the advisory before acting.

🐍 PyPI

Not in CISA KEV

CVE-2026-40934 — jupyter-server

CVE-2026-40934 is a CWE-613 vulnerability in jupyter-server. A fix is available for jupyter-server — see the affected versions and patch details below.

jupyter-server authentication cookies remain valid after password reset due to static cookie secret

Also known asGHSA-5mrq-x3x5-8v8fPYSEC-2026-69

Published

May 5, 2026

Updated

Oct 28, 2026

Affected

1 pkg

Patched

1 / 1

Exploits

None indexed

Exploitation data as of Nov 10, 2026 · OSV.dev, NVD, FIRST.org (EPSS)

Exploitation Status

No confirmed exploitation observed yet

A successful exploit gives an attacker total control of the affected component, not partial access.
CISA’s own triage has not observed active exploitation or public proof-of-concept code for this CVE as of its last assessment.

Exploitation and automatability from CISA’s SSVC triage for CVE-2026-40934.

EPSS Exploitation Probability

via FIRST.org ↗

0.3%probability of exploitation in next 30 days

Lower Risk0.00%

Lower risk than most CVEs27th percentile — riskier than 27% of all scored CVEsHighest risk

Probability of exploitation in the next 30 days, from FIRST.org EPSS.

Real-World Exposure

1 pkg affected

🐍jupyter-server

Real-time download stats are indexed for npm and PyPI packages. This vulnerability affects PyPI packages — download data is not available via public APIs for these ecosystems.

Description

Summary

A persistent cookie secret vulnerability allows authenticated users to maintain indefinite access even after password changes.

The cookie secret used to sign authentication cookies is stored in a permanent file (~/.local/share/jupyter/runtime/jupyter_cookie_secret) that is never automatically rotated or cleared, allowing stolen or compromised cookies to remain valid indefinitely regardless of password resets.

PoC

Start a Jupyter server with password authentication: jupyter server password, jupyter server
Log in with the password and capture the authentication cookie (e.g., just login with a browser).
Change the password to revoke access: jupyter server password
Restart the server
Use the old stolen cookie => remains valid and provides full authenticated access.

Impact

All jupyter-server deployments using password authentication where security incidents may occur
Multi-user systems where one user's compromised session should be revocable by administrators
Shared or public-facing Jupyter servers where credential rotation is a security requirement
Any deployment where password changes are expected to revoke existing sessions

Patches

Jupyter Server 2.18+

Workaround

rm ~/.local/share/jupyter/runtime/jupyter_cookie_secret
# Then restart the server

Affected Packages

1 total 1 fixed

Ecosystem	Package	Vulnerable range	Fix
🐍PyPI	`jupyter-server`	all versions	2.18.0`pip install --upgrade 'jupyter-server==2.18.0'`

Affected Products

1 product · 1 configurations

Application

jupyter serverjupyter

< 2.18.0

range

Detection & mitigation playbook

Open-source dependency

Detect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for jupyter-server, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update jupyter-server to 2.18.0 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-40934 is resolved across your whole dependency graph.
Workarounds
Put an independent control in front of the weakness: restrict the affected endpoint or interface to trusted networks, require an additional authentication factor or proxy-level check, and invalidate existing sessions and credentials in case the flaw has already been used.

Frequently Asked Questions

## Summary A persistent cookie secret vulnerability allows authenticated users to maintain indefinite access even after password changes. The cookie secret used to sign authentication cookies is stored in a permanent file (`~/.local/share/jupyter/runtime/jupyter_cookie_secret`) that is never automatically rotated or cleared, allowing stolen or compromised cookies to remain valid indefinitely regardless of password resets. ## PoC - Start a Jupyter server with password authentication: `jupyter server password`, `jupyter server` - Log in with the password and capture the authentication cooki

O3 Security · Impact-Aware SCA

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