CVE-2026-6658
Deferred Deferred - Pending Action

Cross-site Scripting in Jupyter nbconvert HTML Export

Publication date: 2026-06-26

Last updated on: 2026-06-26

Assigner: huntr.dev

Description
A vulnerability in jupyter/nbconvert versions <= 7.17.0 allows for Cross-site Scripting (XSS) via unsanitized `text/vnd.mermaid` output in HTML exports. The `data_mermaid` block in `share/templates/lab/base.html.j2` renders `text/vnd.mermaid` cell output directly into HTML without escaping, enabling attackers to inject arbitrary HTML/JavaScript by breaking out of the `<pre>` tag. This vulnerability impacts any server using nbconvert to render notebooks as HTML, allowing attackers to execute arbitrary JavaScript in the context of users viewing the HTML export.

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Meta Information

Published
2026-06-26
Last Modified
2026-06-26
Generated
2026-07-17
AI Q&A
2026-06-26
EPSS Evaluated
2026-07-15
NVD
CVE-2026-6658
EUVD
EUVD-2026-39642

Affected Vendors & Products

Showing 1 associated CPE
Vendor Product Version / Range
jupyter nbconvert to 7.17.0 (inc)

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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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Executive Summary

This vulnerability exists in jupyter/nbconvert versions up to 7.17.0 and allows for Cross-site Scripting (XSS) attacks. It occurs because the `text/vnd.mermaid` output in HTML exports is not properly sanitized. Specifically, the `data_mermaid` block in the template `share/templates/lab/base.html.j2` renders this output directly into HTML without escaping it. This flaw enables attackers to inject arbitrary HTML or JavaScript by breaking out of the `<pre>` tag.

As a result, any server using nbconvert to render notebooks as HTML is vulnerable, allowing attackers to execute malicious JavaScript in the context of users who view the HTML export.

Impact Analysis

This vulnerability can impact you by allowing attackers to execute arbitrary JavaScript code in the browsers of users who view the HTML exports generated by nbconvert. This can lead to unauthorized actions such as stealing user credentials, session hijacking, or performing actions on behalf of the user without their consent.

Because the attack exploits Cross-site Scripting, it can compromise the security and privacy of users interacting with the affected HTML exports.

Compliance Impact

This vulnerability allows attackers to execute arbitrary JavaScript in the context of users viewing HTML exports generated by nbconvert. Such Cross-site Scripting (XSS) vulnerabilities can lead to unauthorized access to sensitive information or user data.

Because of the potential for unauthorized data access or manipulation, this vulnerability could negatively impact compliance with data protection standards and regulations such as GDPR and HIPAA, which require safeguarding personal and sensitive information against unauthorized access.

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