CVE-2026-40171

Workarounds

The help extension can be disabled via CLI:

jupyter labextension disable @jupyter-notebook/help-extension
jupyter labextension disable @jupyterlab/help-extension

Hardening

The patched versions include a toggle to disable the command linker functionality altogether, for example via overrides.json:

{
  "@jupyterlab/apputils-extension:sanitizer": {
    "allowCommandLinker": false
  }
}

Resources

• https://jupyterlab.readthedocs.io/en/latest/user/commands.html#commands-in-markdown-output-and-files

Acknowledgments

Reported by Daniel Teixeira - NVIDIA AI Red Team

A stored Cross-Site Scripting (XSS) vulnerability in Jupyter Notebook allows attackers to steal authentication tokens from users who open malicious notebook files and interact with elements that the attacker can make look indistinguishable from legitimate controls (single click interaction).

The vulnerability enables complete account takeover through the Jupyter REST API, allowing the attacker to:

1. Read all files
2. Modify/create files
3. Access running kernels and execute arbitrary code
4. Create terminals for shell access

Untrusted input is rendered as active markup in a victim's browser, which can run script in their session. Typical impact: session or credential theft, and actions taken as the user.

Kodem intelligence

Jupyter Notebook 7.5.6 and JupyterLab 4.5.7 include patches for this vulnerability.

1. What is CVE-2026-40171? CVE-2026-40171 is a high-severity cross-site scripting (XSS) vulnerability in @jupyter-notebook/help-extension (npm), affecting versions >= 7.0.0, <= 7.5.5. It is fixed in 7.5.6, 4.5.7. Untrusted input is rendered as active markup in a victim's browser, which can run script in their session.
2. Which packages are affected by CVE-2026-40171?
   • @jupyter-notebook/help-extension (npm) (versions >= 7.0.0, <= 7.5.5)
   • notebook (pip) (versions >= 7.0.0, <= 7.5.5)
   • jupyterlab (pip) (versions <= 4.5.6)
   • @jupyterlab/help-extension (npm) (versions <= 4.5.6)
3. Is there a fix for CVE-2026-40171? Yes. CVE-2026-40171 is fixed in 7.5.6, 4.5.7. Upgrade to this version or later.
4. Is CVE-2026-40171 exploitable, and should I be worried? Whether CVE-2026-40171 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
5. What actually determines whether CVE-2026-40171 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
6. How do I fix CVE-2026-40171?
   • Upgrade @jupyter-notebook/help-extension to 7.5.6 or later
   • Upgrade notebook to 7.5.6 or later
   • Upgrade jupyterlab to 4.5.7 or later
   • Upgrade @jupyterlab/help-extension to 4.5.7 or later