CVE-2026-6658

Cross-site Scripting (XSS) in jupyter/nbconvert

State: Published
Severity: 5.4 Medium
Published: Jun 26, 2026
Updated: Jun 26, 2026
Reserved: Apr 20, 2026

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.

Scores

CVSS	Score	Vector	Source
3.0	5.4 Medium	CVSS:3.0/AV:N/AC:L/PR:L/UI:R/S:C/C:L/I:L/A:N	@huntr_ai

Weaknesses

CWE-79 Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting')

Affected Products

Product	Versions
jupyter/jupyterjupyter	latest and earlierAffected

References

https://huntr.com/bounties/47570290-3b26-4477-8cfa-fdef7db5aefe

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