# CVE-2026-40934: jupyter-server: Jupyter Server is the backend for Jupyter web applications

CVE-2026-40934 is fixed in jupyter-server on 1 platform by DEBIAN-CVE-2026-40934 (version 2.20.0-1), released May 5, 2026. It is not reported as exploited. Patch Radar priority: Routine.

- Web page: https://patchblox.com/security/cve/CVE-2026-40934
- Priority: Routine
- CVSS: 6.8 (medium)
- EPSS: 0.0033
- CISA KEV: not listed
- Exploited (vendor report): no
- Publicly disclosed: no
- Published: May 5, 2026

## 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.

## Where it's fixed

| Platform | Product | Fixed in | Fix | Released |
|---|---|---|---|---|
| Linux | jupyter-server Debian 14 | 2.20.0-1 | [DEBIAN-CVE-2026-40934](https://patchblox.com/security/data/fix/linux/debian-cve-2026-40934.md) | May 5, 2026 |

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Data as of 2026-11-08T00:53:09Z UTC. Source: Patchblox Patch Radar (https://patchblox.com/security/patch-radar). Patchblox finds out-of-date software on Windows, macOS and Linux and updates it through release rings: https://patchblox.com/demo

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