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High, CVSS 7.6amended

Jupyter Server's Authentication Cookies Remain Valid After Password Reset and Server Restart

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

What to do

Vendor fix available. Upgrade each affected package to the fixed version on its release line (jupyter-server 2.18.0), redeploy, then verify what is actually installed.

This page has no inventory attached, so it cannot say whether you are affected. A vendor fix is not proof that your deployment is fixed.

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Affected packages

Sources

Severity and exploitation
Exploitation
No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.
CVSS 4.0
7.6 · CVSS:4.0/AV:N/AC:L/AT:P/PR:L/UI:N/VC:H/VI:H/VA:N/SC:N/SI:N/SA:N · score source
EPSS
  • CVE-2026-40934: 0.33% estimated exploitation activity in the next 30 days; percentile 26.51 (FIRST EPSS, 2026-11-03). This is a model estimate, not proof of exploitation or customer exposure.
Source description

As published by the source; long descriptions are shortened.

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/jupytercookiesecret) 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…

Dates and revisions
Published by the source
Last modified by the source
Source last checked
  1. Revision 3 · amended ·

    Amended from ghsa record GHSA-5mrq-x3x5-8v8f

  2. Revision 2 · amended ·

    Reviewed OSV alias/range/CVSS4 correction; package source scopes and original publication preserved. No customer finding resolved.

  3. Revision 1 · created ·

    Published from osv record GHSA-5mrq-x3x5-8v8f

Agent brief

Preview the exact text before you copy it. Commands are read-only suggestions; review them before running anything.

# Patch Next advisory brief: CVE-2026-40934

Advisory: Jupyter Server's Authentication Cookies Remain Valid After Password Reset and Server Restart
IDs: CVE-2026-40934, GHSA-5mrq-x3x5-8v8f
Record: https://patchnext.com/advisories/cve-2026-40934 (revision 3, source checked 26 Oct 2026, 13:42 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: High (CVSS 7.6)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: jupyter-server 2.18.0. A vendor fix does not mean a deployment is fixed.

## Affected components
- PyPI jupyter-server: affected <= 2.17.0; fixed in 2.18.0

## Suggested inspection (read-only)
- `python -m pip show jupyter-server`: prints the installed version. Run with the environment that serves production active.

## Supported action
Upgrade each affected component to a fixed version on its release line. For a transitive dependency, upgrade the parent package or add an override or constraint, then regenerate the lockfile. Redeploy every environment that ran an affected version.

## Required regression checks
- Run the test suite and a production build.
- Exercise the features that depend on jupyter-server.
- Repeat the inspection and confirm that only fixed versions remain installed.

## Rollback considerations
- Keep the previous lockfile and deployment artifact. Rolling back reinstates the vulnerable version, so apply any documented mitigation while you fix forward.

## Unresolved questions
- Which deployments run an affected version?
- Exploitation status can change. Check again before lowering the priority.
- Mark the work resolved only after the fixed version is verified in production.

## Sources
- Verified: https://osv.dev/vulnerability/GHSA-5mrq-x3x5-8v8f (OSV record GHSA-5mrq-x3x5-8v8f lists affected ranges: PyPI jupyter-server >=0 <2.18.0 (fixed))
- Verified: https://github.com/advisories/GHSA-5mrq-x3x5-8v8f (GitHub-reviewed advisory GHSA-5mrq-x3x5-8v8f lists affected ranges: PyPI jupyter-server >=0 <=2.17.0)

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