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

Source: https://junglewise.ai/threats/cve-2026-42266-project-jupyter-jupyterlab-privilege-escalation-in-pypi-extension  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-05-13. Updated: 2026-05-21  
License: CC BY 4.0 with a link back

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](https://junglewise.ai/threats/technologies/jupyterlab), [jupyterlab (PyPI)](https://junglewise.ai/threats/technologies/pypi-jupyterlab). Vendors: [Project Jupyter](https://junglewise.ai/threats/vendors/project-jupyter), [PyPI](https://junglewise.ai/threats/vendors/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

  ```sh
  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

- [https://github.com/jupyterlab/jupyterlab/releases/tag/v4.5.7](https://github.com/jupyterlab/jupyterlab/releases/tag/v4.5.7)
- [https://github.com/jupyterlab/jupyterlab/security/advisories/GHSA-37w4-hwhx-4rc4](https://github.com/jupyterlab/jupyterlab/security/advisories/GHSA-37w4-hwhx-4rc4)
- [https://jupyterhub.readthedocs.io/en/5.2.1/explanation/websecurity.html](https://jupyterhub.readthedocs.io/en/5.2.1/explanation/websecurity.html)
- [https://jupyterlab.readthedocs.io/en/latest/user/extensions.html](https://jupyterlab.readthedocs.io/en/latest/user/extensions.html)

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