CVE-2026-42266: Project Jupyter JupyterLab privilege escalation in PyPI Extension Manager

CVE-2026-42266 · Severity: high · CVSS 8.8 · Published 2026-05-13

JupyterLab is an interactive computing environment used by data scientists and researchers to write and run code. A security flaw in the extension manager allows authenticated users to bypass restrictions on which software extensions can be installed. In shared or multi-tenant environments, such as a university JupyterHub, this could allow a user to escalate their privileges, steal data, or gain persistent access to the underlying server infrastructure.

Technologies: Project Jupyter JupyterLab, jupyterlab (PyPI). Vendors: Project Jupyter, PyPI.

Quick answers

Is CVE-2026-42266 exploited in the wild?
No. Junglewise Threat Intelligence has no report of CVE-2026-42266 being exploited in the wild.
How severe is CVE-2026-42266?
High severity, with a CVSS score of 8.8, published 13 May 2026.
Which products and versions are affected?
Project Jupyter JupyterLab >=4.0.0, <=4.5.6, 4.0.0 to 4.5.6; jupyterlab (PyPI) ECOSYSTEM:introduced=4.0.0,fixed=4.5.7.
Is there a fix for CVE-2026-42266?
Yes. jupyterlab (PyPI): upgrade to 4.5.7 or later. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.
How is CVE-2026-42266 attacked?
It is attacked over the network, in a network appliance.
Am I affected by CVE-2026-42266?
Check whether you run Project Jupyter JupyterLab or jupyterlab (PyPI) at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

How to fix

  • jupyterlab (PyPI): upgrade to 4.5.7 or later
    pip install "jupyterlab>=4.5.7"

Technical details

JupyterLab versions 4.0.0 through 4.5.6 contain a vulnerability where the 'allowed_extensions_uris' configuration is not correctly enforced. The PyPI Extension Manager fails to restrict package installation to the default PyPI index or the specified allow-list, leading to potential argument injection (CWE-88) or client-side enforcement issues (CWE-602). An authenticated attacker in a multi-tenant or shared deployment (like JupyterHub) can exploit this to install malicious extensions, resulting in privilege escalation, lateral movement, or persistent server compromise. The issue is fixed in version 4.5.7; a workaround is to set the extension manager to 'readonly' mode.

Affected products

  • Project Jupyter JupyterLab 4.0.0 to 4.5.6

Identifiers

  • CVE-2026-42266
  • GHSA-37w4-hwhx-4rc4
  • PYSEC-2026-164

Timeline

  • 2026-04-29: patched: Version 4.5.7 released with security fixes.
  • 2026-04-30: advisory: GitHub security advisory GHSA-37w4-hwhx-4rc4 published.
  • 2026-05-13: disclosed: CVE-2026-42266 published to NVD.

References

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