CVE-2026-40934

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

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.