---
title: "CVE-2026-40171\n    | Ubuntu"
description: Ubuntu is an open source software operating system that runs from the
  desktop, to the cloud, to all your internet connected things.
url: https://ubuntu.com/security/CVE-2026-40171?format=md
keywords: index, follow
---

# CVE-2026-40171

Publication date 6 May 2026

Last updated 10 July 2026

---

Ubuntu priority

**Medium**

[Why this priority?](https://ubuntu.com/security/cves/about#priority )

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## Description

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
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.

## Status

Show unmaintained releases

| Package | Ubuntu Release | Status |
| --- | --- | --- |
| jupyter-notebook | 26.04 LTS resolute | Needs evaluation |
| 25.10 questing | Ignored end of life, was needs-triage |
| 24.04 LTS noble | Needs evaluation |
| 22.04 LTS jammy | Needs evaluation |
| 20.04 LTS focal | Needs evaluation |
| 18.04 LTS bionic | Needs evaluation |

---

* [How can I get the fixes?](https://ubuntu.com/security/cves/about#security)
* [What do statuses mean?](https://ubuntu.com/security/cves/about#statuses)

## Severity score breakdown

CVSS version:
CVSS v4.0

**Base score**

8.4 · High

* Base metrics

  | Parameter | Value |
  | --- | --- |
  | Attack vector | Network |
  | Attack complexity | Low |
  | Attack requirements | None |
  | Privileges required | High |
  | User interaction | Active |
  | Vulnerable system - Confidentiality impact | High |
  | Vulnerable system - Integrity impact | High |
  | Vulnerable system - Availability impact | High |
  | Subsequent system - Confidentiality impact | None |
  | Subsequent system - Integrity impact | None |
  | Subsequent system - Availability impact | None |
* Scores

  | Parameter | Value |
  | --- | --- |
  | Base score | 8.4 · High |
  | Base + Threat score | - |
  | Base + Environmental score | - |
  | Base + Threat + Environmental score | - |

**Vector:** CVSS:4.0/AV:N/AC:L/AT:N/PR:H/UI:A/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N

## References

* [MITRE](https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2026-40171)
* [NVD](https://nvd.nist.gov/vuln/detail/CVE-2026-40171)
* [Launchpad](https://launchpad.net/bugs/cve/CVE-2026-40171)
* [Debian](https://security-tracker.debian.org/tracker/CVE-2026-40171)

### Other references

* <https://www.cve.org/CVERecord?id=CVE-2026-40171>