CVE-2026-40934 jupyter-server authentication cookies remain valid after password reset due to static cookie secret
Attackers retain authenticated access after password resets because Jupyter Server fails to rotate the cookie signing secret, allowing session hijacking.
- Exploited in the wild
- Not known
- Login needed
- Any signed-in user
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-40934?
CVE-2026-40934 is a high-severity authentication bypass vulnerability in jupyter-server jupyter_server, published on 5 May 2026. Any signed-in user can exploit it over the network, with no action from the victim.
Official 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.
Weakness: CWE-613
Which versions are affected by CVE-2026-40934?
3 open source packages ship an affected version, including jupyter-server. It affects 1 product.
| Package | Affected | Fixed in |
|---|---|---|
jupyter-server PyPI | All versions | 2.18.0 |
jupyter-server PyPI | All versions | 2.18.0 |
jupyter-server PyPI | All versions | 2.18.0 |
Products include Jupyter Jupyter Server.
How do I fix CVE-2026-40934?
Upgrade jupyter-server to 2.18.0 or later.
Upgrade, and rotate credentials and sessions that may have been exposed. More about Authentication bypass.
Is CVE-2026-40934 being exploited?
There is no known exploitation of CVE-2026-40934 in the wild and no public exploit code.
Other vulnerabilities in jupyter-server jupyter_server
- CVE-2026-44727 Jupyter Server: Stored XSS in `NbconvertFileHandler` / `NbconvertPostHandler` via missing `sandbox` CSP
- CVE-2026-35397 jupyter-server path traversal allows access to sibling directories sharing root_dir name prefix
- CVE-2026-40110 jupyter-server CORS origin validation bypass via unanchored regex in allow_origin_pat
- CVE-2024-35178 Jupyter server on Windows discloses Windows user password hash
- CVE-2022-24757 Sensitive Auth & Cookie data stored in Jupyter server logs
Sources
Also known as CLEANSTART-2026-HV39439, CLEANSTART-2026-PZ41099, DEBIAN-CVE-2026-40934, GHSA-5mrq-x3x5-8v8f, PYSEC-2026-69, UBUNTU-CVE-2026-40934.