---
id: CVE-2026-6658
aliases:
  - GHSA-9754-6rhw-gj3h
title: >-
  jupyter/nbconvert allows Cross-site Scripting (XSS) via unsanitized
  `text/vnd.mermaid` output in HTML exports
summary: >-
  jupyter/nbconvert allows Cross-site Scripting (XSS) via unsanitized
  `text/vnd.mermaid` output in HTML exports
severity: medium
cvss: 5.4
cvssVector: 'CVSS:3.0/AV:N/AC:L/PR:L/UI:R/S:C/C:L/I:L/A:N'
vendor: nbconvert
product: nbconvert
ecosystem: pip
affected:
  - nbconvert <= 7.17.0
published: '2026-06-26'
updated: '2026-11-06'
sourceUpdated: '2026-11-06T18:00:04.178054901Z'
source: OSV
sourceUrl: 'https://osv.dev/vulnerability/GHSA-9754-6rhw-gj3h'
references:
  - url: 'https://nvd.nist.gov/vuln/detail/CVE-2026-6658'
  - url: 'https://github.com/jupyter/nbconvert'
  - url: 'https://huntr.com/bounties/47570290-3b26-4477-8cfa-fdef7db5aefe'
  - url: 'https://github.com/advisories/GHSA-9754-6rhw-gj3h'
tags:
  - osv
  - pip
  - ghsa
epss: 0.00161
epssPercentile: 0.05287
cwe:
  - CWE-79
ingestedAt: '2026-11-06T18:00:12.490Z'
---

## Overview

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.

## Affected packages

- `nbconvert <= 7.17.0`

## Remediation

Refer to the advisory for the patched release.