Bug 2466909 (CVE-2026-40934)

Summary:	CVE-2026-40934 jupyter-server: Jupyter Server: Authentication bypass due to unrotated cookie secret
Product:	[Other] Security Response	Reporter:	OSIDB Bzimport <bzimport>
Component:	vulnerability	Assignee:	Product Security DevOps Team <prodsec-dev>
Status:	NEW ---	QA Contact:
Severity:	medium	Docs Contact:
Priority:	medium
Version:	unspecified	CC:	jkoehler, lphiri, rjohnson
Target Milestone:	---	Keywords:	Security
Target Release:	---
Hardware:	All
OS:	Linux
Whiteboard:
Fixed In Version:		Doc Type:	---
Doc Text:	A flaw was found in Jupyter Server. The secret used to sign authentication cookies is not rotated when a user changes their password, allowing previously issued authentication cookies to remain valid. A remote attacker who has captured a session cookie can retain full authenticated access to the server, even after a password reset and server restart. This vulnerability impacts deployments using password-based authentication, especially shared or public-facing servers where credential rotation is expected to revoke existing sessions.	Story Points:	---
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Last Closed:		Type:	---
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Verified Versions:		Category:	---
oVirt Team:	---	RHEL 7.3 requirements from Atomic Host:
Cloudforms Team:	---	Target Upstream Version:
Embargoed:
Bug Depends On:	2484714, 2484713
Bug Blocks:

Description OSIDB Bzimport 2026-05-05 22:01:24 UTC

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.