🛡️ CVE-2026-6658

🟡 CVSS 5.4 — Medium ✅ No Known Exploit CWE-79 NVD
5.4
CVSS Score
0 Low4 Medium7 High9 Critical10

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.

How this vulnerability can be exploited

This issue can be reached over the network, attack complexity is low, an attacker needs low-level privileges on the target. A user must be tricked into taking some action. The scope is changed, meaning a successful attack can affect components beyond the vulnerable one. Rated impact: confidentiality low, integrity low, availability none.

Weakness class

CVE-2026-6658 is classified as CWE-79: Cross-site Scripting (XSS). User-supplied data is written into a page without escaping, so attacker script runs in the browser of anyone who views it.

Affected software

CVE-2026-6658 is recorded against 1 package.

  • unknown

Timeline and source

Published on 26 June 2026. No public exploit is currently recorded for this entry. Record sourced from NVD.

References

huntr.com
huntr.com

Details

Severity MEDIUM
CVSS Score 5.4
CVSS Vector CVSS:3.0/AV:N/AC:L/PR:L/UI:R/S:C/C:L/I:L/A:N
CWE CWE-79
Public Exploit ✅ No
Source NVD
Published 2026-06-26
Updated 2026-08-11
Modified 2026-06-26
Fix URL N/A

Affected Packages

Software From version Fixed in
unknown — —

Similar Threats

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