CVE-2026-42557: jupyterlab: Command linker attributes in HTML enable one-click command execution from untrusted content

Severity: critical (CVSS 9.6 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 0.4% probability of exploitation in the next 30 days
Public exploit or detection template: none known
Published: 2026-05-13 · updated 2026-10-25
Weakness: CWE-79

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.

Affected products

jupyterlab: before 4.5.7 — fixed in 4.5.7
jupyter notebook: from 7.0.0 before 7.5.6 — fixed in 7.5.6

How to fix

Upgrade to a fixed version: jupyterlab 4.5.7; jupyter notebook 7.5.6. Check the vendor advisory for mitigations.

References

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