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)?

If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.

How does O3 Security protect against CVE-2026-40171?

O3 Security's impact-aware SCA analyses which vulnerable code paths your application actually calls, so a match like CVE-2026-40171 can be triaged on real exposure rather than presence alone.

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 40th 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 August 12, 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

Aug 12, 2026

Affected

4 pkgs

Patched

4 / 4

Exploits

None indexed

Exploitation data as of Sep 19, 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 CVEs40th percentile — riskier than 40% of all scored CVEsHighest risk

EPSS (Exploit Prediction Scoring System) is a daily probability model maintained by FIRST.org. It estimates the likelihood a CVE will be exploited in production environments within the next 30 days, derived from real-world threat intelligence signals.

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

179downloads / week

@jupyterlab/help-extensionnpm

6Kdownloads / week

Description

An attacker can craft a malicious notebook file containing elements that appear indistinguishable from legitimate controls and trigger execution when a user interacts with them. Successful exploitation allows theft of the user's authentication token and complete takeover of the Jupyter session through the REST API, including reading files, creating or modifying files, accessing kernels to execute arbitrary code, and creating terminals for shell access. This issue has been fixed in Notebook 7.5.6, JupyterLab 4.5.7, @jupyter-notebook/help-extension 7.5.6, and @jupyterlab/help-extension 4.5.7. As a workaround, disable the affected help extensions or set allowCommandLinker to false in the sanitizer configuration.

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
If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.
How O3 protects you
O3 Security's impact-aware SCA analyses which vulnerable code paths your application actually calls, so a match like CVE-2026-40171 can be triaged on real exposure rather than presence alone.

Tailored to CVE-2026-40171. Runtime protection reduces exposure until a permanent patch is applied and verified — it complements patching, it doesn't replace it.

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…

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

In Jupyter Notebook versions 7.0.0 through 7.5.5, JupyterLab versions 4.5.6 and earlier, and the corresponding @jupyter-notebook/help-extension and @jupyterlab/help-extension packages before 7.5.6 and 4.5.7, a stored cross-site scripting issue in the help command linker can be chained with attacker-controlled notebook content to steal authentication tokens with a single click. An attacker can craft a malicious notebook file containing elements that appear indistinguishable from legitimate controls and trigger execution when a user interacts with them. Successful exploitation allows theft of t

O3 Security · Impact-Aware SCA

Is CVE-2026-40171 in your dependencies?

O3 Security finds CVE-2026-40171 across npm, PyPI dependencies, including transitive ones, and its impact-aware SCA ranks findings by whether your code actually calls the vulnerable path.

Scan my dependencies How O3 SCA works