CVE-2026-42266

JupyterLab is an extensible environment for interactive and reproducible computing, based on the Jupyter Notebook Architecture. From 4.0.0 to 4.5.6, the allow-list of extensions that can be installed from PyPI Extension Manager (allowed_extensions_uris) is not correctly enforced by JupyterLab. The PyPI Extension Manager was not contained to packages listed on the default PyPI index. This vulnerability is fixed in 4.5.7.

What this means for your business

It affects Jupyterlab. It matters if your company, or a supplier that handles your data, runs it.
An attacker can use it remotely, over a network, with an ordinary user login, and without anyone at your company clicking anything.
FIRST's prediction model gives it a 0.6% chance of attack attempts being seen in the next 30 days, ranking above 48% of all known flaws.

What to do

1Check whether your company or your suppliers run Jupyterlab, and which version. The affected versions are listed further down this page.
2If you do, apply the vendor's fix. A patch or vendor advisory has been published.

Not sure if your company is exposed?

Fastnexa’s certified penetration testers can check whether attackers could use this flaw, or others like it, against your websites, apps and network. The full test is free for our first 10 founding clients until 31 December 2026.

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Scoring

CVSS: 8.8 (v3.1)
Vector: CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
Weakness: CWE-88
Assigned by: security-advisories@github.com

Dates

Published: 2026-05-13
Last modified: 2026-08-28
Sources: NVD

Affected products

Jupyter Jupyterlab4.0.0 - 4.5.7

As listed in the NVD configuration data. Not a statement about your estate.