How severe is CVE-2026-40171?

No CVSS score has been assigned to CVE-2026-40171 yet. Review the advisory details and affected package list to assess your exposure.

Which packages are affected by CVE-2026-40171?

CVE-2026-40171 affects the following packages: @jupyter-notebook/help-extension (npm), @jupyterlab/help-extension (npm), notebook (PyPI), jupyterlab (PyPI). Ecosystems affected: npm, PyPI.

How do I fix CVE-2026-40171?

Update @jupyter-notebook/help-extension to 7.5.6 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-40171 is resolved across your whole dependency graph.

How do I detect CVE-2026-40171 in my npm, PyPI dependencies?

Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for @jupyter-notebook/help-extension, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.

How do I mitigate CVE-2026-40171 if there is no patch (or I can't update yet)?

Escape or sanitise the affected output on the server side rather than relying on client-side filtering, and add a Content-Security-Policy that blocks inline script execution so injected markup cannot run even if it reaches the page.

Is CVE-2026-40171 actively exploited in the wild?

No public exploit code has been indexed for CVE-2026-40171 yet. This does not mean the vulnerability cannot be exploited — absence of public exploits does not imply safety. Apply the recommended fix and use O3 Security to monitor your exposure.

What is the EPSS score for CVE-2026-40171?

CVE-2026-40171 has an EPSS (Exploit Prediction Scoring System) score of 0.5%, placing it in the 41th percentile of all CVEs. EPSS is maintained by FIRST.org and estimates the probability that a vulnerability will be exploited in the wild within the next 30 days. This score indicates relatively lower exploitation probability, though the CVSS severity should still guide your patching priority.

What type of vulnerability is CVE-2026-40171?

CVE-2026-40171 is classified as Cross-site Scripting (XSS) (CWE-79). This weakness type describe the underlying flaw category, which helps determine the potential impact and the right class of mitigation. This is a high-impact weakness class that often enables remote code execution or data exposure.

When was CVE-2026-40171 published, and has it been updated?

CVE-2026-40171 was published on May 6, 2026 and was last updated on October 28, 2026. Advisory data evolves as severity scores, affected ranges, and exploit intelligence are revised — always check the latest version of the advisory before acting.

📦 npm🐍 PyPI

Not in CISA KEV

CVE-2026-40171 — @jupyter-notebook/help-ex…

CVE-2026-40171 is a Cross-site Scripting (XSS) vulnerability in @jupyter-notebook/help-extension. A fix is available for @jupyter-notebook/help-extension — see the affected versions and patch details below.

Jupyter Notebook and JupyterLab token theft via stored XSS in help command linker

Also known asBIT-jupyter-base-notebook-2026-40171BIT-jupyter-notebook-2026-40171BIT-jupyterlab-2026-40171GHSA-rch3-82jr-f9w9PYSEC-2026-2538PYSEC-2026-2682

Published

May 6, 2026

Updated

Oct 28, 2026

Affected

4 pkgs

Patched

4 / 4

Exploits

None indexed

Exploitation data as of Nov 7, 2026 · OSV.dev, NVD, FIRST.org (EPSS)

Exploitation Status

No confirmed exploitation observed yet

A successful exploit gives an attacker total control of the affected component, not partial access.
CISA’s own triage has not observed active exploitation or public proof-of-concept code for this CVE as of its last assessment.

Exploitation and automatability from CISA’s SSVC triage for CVE-2026-40171.

EPSS Exploitation Probability

via FIRST.org ↗

0.5%probability of exploitation in next 30 days

Lower Risk0.00%

Lower risk than most CVEs41th percentile — riskier than 41% of all scored CVEsHighest risk

Probability of exploitation in the next 30 days, from FIRST.org EPSS.

Real-World Exposure

4 pkgs affected

How broadly this vulnerability is actually deployed: weekly install volume shows current usage, and reverse-dependency count shows how many other packages break if it stays unpatched.

0other npm packages depend on this — each one inherits the vulnerability until it's patched upstream

@jupyter-notebook/help-extensionnpm

734downloads / week

@jupyterlab/help-extensionnpm

15Kdownloads / week

Description

Impact

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:

Read all files
Modify/create files
Access running kernels and execute arbitrary code
Create terminals for shell access

Patches

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

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

Affected Packages

4 total 4 fixed

Ecosystem	Package	Vulnerable range	Fix
📦npm	`@jupyter-notebook/help-extension`	≥ 7.0.0&&< 7.5.6	7.5.6`npm install @jupyter-notebook/help-extension@7.5.6`
📦npm	`@jupyterlab/help-extension`	all versions	4.5.7`npm install @jupyterlab/help-extension@4.5.7`
🐍PyPI	`notebook`	≥ 7.0.0&&< 7.5.6	7.5.6`pip install --upgrade 'notebook==7.5.6'`
🐍PyPI	`jupyterlab`	all versions	4.5.7`pip install --upgrade 'jupyterlab==4.5.7'`

Detection & mitigation playbook

Open-source dependency

Detect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for @jupyter-notebook/help-extension, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update @jupyter-notebook/help-extension to 7.5.6 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-40171 is resolved across your whole dependency graph.
Workarounds
Escape or sanitise the affected output on the server side rather than relying on client-side filtering, and add a Content-Security-Policy that blocks inline script execution so injected markup cannot run even if it reaches the page.

Fixing This On Your OS

If you run this on a Linux distribution, patch through your package manager against the distro's own security advisory below — it tracks the exact backported fix for your release, which can ship on a different timeline (and sometimes a different severity) than the upstream project.

Red HatImportant

This is an Important flaw in Jupyter Notebook and JupyterLab, enabling a stored cross-site scripting (XSS) attack. An attacker can craft a malicious notebook that, with a single user click, can steal authentication tokens and fully compromise the Jupyter session, leading to arbitrary code execution and information…

Workaround published by Red Hat

To reduce the risk of exploitation, disable the affected help extensions in Jupyter Notebook and JupyterLab, or set the `allowCommandLinker` option to `false` within the sanitizer configuration. Consult the Jupyter documentation for specific instructions on modifying these settings. Disabling these features may affect the availability of certain help functionalities.

Source: Red Hat security advisory for CVE-2026-40171 (CC BY 4.0)

Product	Fixed in	Advisory
Red Hat Migration Toolkit for Applications 8.2	`mta/mta-solution-server-rhel9:1784109883`	RHSA-2026:43038
Red Hat OpenShift AI 2.25	`rhoai/odh-workbench-jupyter-datascience-cpu-py312-rhel9:1788315638`	RHSA-2026:65126
Red Hat OpenShift AI 3.4	`rhoai/odh-th06-cpu-torch210-py312-rhel9:1787076778`	RHSA-2026:60520

Frequently Asked Questions

### Impact 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 ### Patches Jupyter Notebook 7.5.6 and JupyterLab 4.5