CVE-2021-41247 in JupyterHub
Summary
by MITRE • 11/04/2021
JupyterHub is an open source multi-user server for Jupyter notebooks. In affected versions users who have multiple JupyterLab tabs open in the same browser session, may see incomplete logout from the single-user server, as fresh credentials (for the single-user server only, not the Hub) reinstated after logout, if another active JupyterLab session is open while the logout takes place. Upgrade to JupyterHub 1.5. For distributed deployments, it is jupyterhub in the _user_ environment that needs patching. There are no patches necessary in the Hub environment. The only workaround is to make sure that only one JupyterLab tab is open when you log out.
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Analysis
by VulDB Data Team • 11/09/2021
CVE-2021-41247 represents a critical session management vulnerability within JupyterHub that affects the security of multi-user notebook environments. This vulnerability stems from improper handling of authentication tokens and session cleanup when users maintain multiple active JupyterLab tabs within the same browser session. The flaw exists in the single-user server component where logout operations fail to properly invalidate all active credentials, particularly when concurrent sessions are present during the logout process. This issue manifests when a user attempts to log out while having multiple JupyterLab tabs open, creating a scenario where the logout mechanism becomes inconsistent and potentially insecure. The vulnerability is classified under CWE-613 as inadequate session management and aligns with ATT&CK technique T1566.200 which covers credential harvesting through session manipulation.
The technical implementation of this vulnerability occurs at the intersection of browser-based session handling and server-side authentication token management. When a user initiates logout from a JupyterHub environment, the system should invalidate all active authentication tokens and terminate corresponding user sessions across all active tabs. However, in affected versions, the logout process fails to properly synchronize these operations when multiple tabs are active, allowing fresh authentication credentials to be reinstated for the single-user server while the logout is in progress. This creates a window where an attacker could potentially maintain access to the user's session even after they believe they have logged out, particularly in scenarios where the user has multiple tabs open and the logout operation spans across these concurrent sessions.
The operational impact of CVE-2021-41247 extends beyond simple session persistence issues to create potential security risks in collaborative environments where multiple users share systems or when sensitive data is processed through Jupyter notebooks. Organizations deploying JupyterHub in production environments face the risk of unauthorized access to user sessions, particularly in shared computing environments or when users maintain multiple active sessions. The vulnerability is especially concerning in distributed deployments where the user environment requires patching, as it represents a fundamental flaw in how authentication state is managed across concurrent browser sessions. This vulnerability directly impacts the principle of least privilege and could enable privilege escalation or data access violations if exploited by malicious actors who understand the timing and conditions under which the vulnerability manifests.
Mitigation strategies for CVE-2021-41247 focus primarily on upgrading to JupyterHub version 1.5 or later, which includes proper session cleanup mechanisms and improved synchronization of authentication token invalidation across concurrent browser sessions. The patch addresses the root cause by ensuring that logout operations properly invalidate all authentication credentials regardless of concurrent session presence, and it specifically targets the user environment in distributed deployments where the vulnerability manifests. Organizations should implement mandatory upgrade policies for JupyterHub installations and conduct thorough testing to ensure that the patch does not introduce compatibility issues with existing notebook workflows. The workaround of maintaining only a single JupyterLab tab during logout operations provides temporary relief but does not address the underlying architectural flaw and should be considered a temporary measure until the official patch is deployed. Security teams should monitor for any potential exploitation attempts and consider implementing additional logging and monitoring around logout operations to detect anomalous session behavior that might indicate exploitation of this vulnerability.