CVE-2026-40171
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Stored XSS in Jupyter Notebook and JupyterLab Help Extensions

Publication date: 2026-05-06

Last updated on: 2026-05-06

Assigner: GitHub, Inc.

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.
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Meta Information
Published
2026-05-06
Last Modified
2026-05-06
Generated
2026-06-16
AI Q&A
2026-05-07
EPSS Evaluated
2026-06-14
NVD
CVE-2026-40171
Affected Vendors & Products
Showing 8 associated CPEs
Vendor Product Version / Range
jupyter notebook From 7.0.0 (inc) to 7.5.5 (inc)
jupyter jupyterlab to 4.5.6 (inc)
jupyter notebook_help_extension to 7.5.6 (exc)
jupyter jupyterlab_help_extension to 4.5.7 (exc)
jupyter notebook 7.5.6
jupyter jupyterlab 4.5.7
jupyter notebook_help_extension 7.5.6
jupyter jupyterlab_help_extension 4.5.7
Helpful Resources
Exploitability
CWE
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KEV
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CWE ID Description
CWE-79 The product does not neutralize or incorrectly neutralizes user-controllable input before it is placed in output that is used as a web page that is served to other users.
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Compliance Impact

This vulnerability allows an attacker to steal authentication tokens and take over Jupyter sessions, potentially leading to unauthorized access to sensitive data and execution of arbitrary code.

Such unauthorized access and data exposure could impact compliance with standards and regulations like GDPR and HIPAA, which require protection of personal and sensitive information and mandate controls to prevent unauthorized access.

However, the provided information does not explicitly describe the direct effects on compliance with these standards.

Executive Summary

This vulnerability exists in Jupyter Notebook versions 7.0.0 through 7.5.5, JupyterLab versions 4.5.6 and earlier, and related help-extension packages before certain fixed versions. It is a stored cross-site scripting (XSS) issue in the help command linker that can be exploited by an attacker who crafts a malicious notebook file.

The malicious notebook contains elements that look like legitimate controls and can trigger execution when a user interacts with them. This allows the attacker to steal the user's authentication token with a single click.

With the stolen token, the attacker can fully take over the Jupyter session via the REST API, including reading and modifying files, executing arbitrary code through kernels, and creating terminals for shell access.

The issue has been fixed in Notebook 7.5.6, JupyterLab 4.5.7, and corresponding help-extension versions. Workarounds include disabling the affected help extensions or setting allowCommandLinker to false in the sanitizer configuration.

Impact Analysis

This vulnerability can have severe impacts including complete takeover of your Jupyter session.

  • The attacker can steal your authentication token.
  • They can read and modify your files.
  • They can execute arbitrary code by accessing kernels.
  • They can create terminals to gain shell access.

This means an attacker can fully control your Jupyter environment, potentially leading to data loss, unauthorized data access, and system compromise.

Mitigation Strategies

To mitigate this vulnerability, you should upgrade to the fixed versions: 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, you can disable the affected help extensions or set allowCommandLinker to false in the sanitizer configuration.

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