Medium [CVE-2026-6658] Cross-site Scripting via unsanitized Mermaid output in HTML exports
This medium-severity Red Hat Linux advisory covers CVE-2026-6658 affecting Migration Toolkit for Applications 8, Red Hat OpenShift AI (RHOAI), Red Hat Satellite 6.
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VulniPulse record published Record updated
Summary
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 `` 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. A flaw was found in nbconvert.
This vulnerability allows a remote attacker to perform Cross-site Scripting (XSS) by injecting arbitrary HTML or JavaScript code. The vulnerability arises from improper sanitization of `text/vnd.mermaid` output during HTML export, enabling injection of malicious code when a user views an exported notebook from an untrusted source.
This impacts Red Hat OpenShift AI, Migration Toolkit for Applications, and Red Hat Satellite, where `nbconvert` is utilized for notebook rendering. Red Hat severity: Moderate — CVSS 5.4 (CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:C/C:L/I:L/A:N).
Weakness: CWE-79. Red Hat does not currently list a fixing RHSA for this CVE.
Affected products named by the advisory: Migration Toolkit for Applications 8; Red Hat OpenShift AI (RHOAI); Red Hat Satellite 6.
Is CVE-2026-6658 exploited?
No exploitation is reported in the sources VulniPulse tracks: CVE-2026-6658 is not in the CISA KEV catalog (checked ) and this advisory does not report exploitation. That is not proof the vulnerability cannot be exploited.
How do I fix CVE-2026-6658?
The advisory VulniPulse tracks names no fixed release. Follow Red Hat's guidance for workarounds and updates.
Confirm against the vendor advisory before you patch.
Affected versions
No affected-version range was extracted from the source record. The vendor advisory is authoritative. Check it before change work.
Official advisory · high-confidence parse· fetched 13 days ago·verify at source
Fixed versions
No fixed release is recorded yet. That does not prove no patch exists. Confirm against the vendor advisory.
Official advisory · high-confidence parse· fetched 13 days ago·verify at source
Mitigation checklist
- Users should avoid exporting or viewing untrusted notebooks as HTML to prevent the execution of arbitrary JavaScript.
Official advisory · high-confidence parse· fetched 13 days ago·verify at source
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