CVE-2026-42557

Description

jupyterlab is an extensible environment for interactive and reproducible computing, based on the Jupyter Notebook Architecture. Prior to 4.5.7, JupyterLab's HTML sanitizer allowlists data-commandlinker-command and data-commandlinker-args on button elements, while CommandLinker listens for all click events on document.body and executes the named command without checking whether the element came from trusted JupyterLab UI. A notebook with a pre-saved HTML cell output containing a deceptive button can trigger arbitrary JupyterLab commands - including arbitrary code execution - on a single user click, without any code being submitted for execution by the user. This vulnerability is fixed in 4.5.7.

How to fix CVE-2026-42557

To remediate CVE-2026-42557, upgrade the affected package to a fixed version below.

• —upgrade to 7.5.6 or later
• —upgrade to 7.5.6 or later
• —upgrade to 4.5.7 or later
• —upgrade to 4.5.7 or later
• —upgrade to 4.5.7 or later
• —upgrade to 7.5.6 or later
• —upgrade to 7.5.6 or later

Is CVE-2026-42557 being exploited?

Low — EPSS is 0.4%, meaning exploitation activity has not been observed at scale.

Affected packages (7)

• >= 7.0.0, < 7.5.6
• >= 7.0.0, < 7.5.6
• from 0, < 4.5.7
• from 0, < 4.5.7
• from 0, < 4.5.7
• >= 7.0.0, < 7.5.6
• >= 7.0.0, < 7.5.6

CVSS scores

References (10)

• ADVISORYgithub.com/advisories/GHSA-mqcg-5x36-vfcg
• ADVISORYnvd.nist.gov/vuln/detail/CVE-2026-42557
• PATCHgithub.com/jupyterlab/jupyterlab
• PATCHpypi.org/project/jupyterlab
• PATCHpypi.org/project/notebook