Medium [CVE-2026-59926] Cross-Site Scripting via unescaped HTML class attribute in Admonition directive
This medium-severity Red Hat Linux advisory covers CVE-2026-59926 affecting Migration Toolkit for Applications 8, Red Hat OpenShift AI (RHOAI), Red Hat OpenShift Container Platform 4.
Aggregated and source-linked by VulniPulse. Data sources, validation and limitations.
VulniPulse record published Record updated
Summary
Mistune is a Python Markdown parser with renderers and plugins. Prior to 3.2.1, render_admonition() in src/mistune/directives/admonition.py concatenates the Admonition directive:class: option into the HTML class attribute without escaping, allowing attribute injection and cross-site scripting even when HTMLRenderer escape mode is enabled.
This issue is fixed in version 3.2.1. A remote attacker could exploit this by providing specially crafted input, leading to the execution of arbitrary script code in the user's browser.
This Moderate flaw in the Mistune Markdown parser allows for Cross-Site Scripting (XSS) due to improper sanitization of user-controlled input within the Admonition directive's class attribute. This vulnerability requires user interaction with malicious content for successful exploitation.
Red Hat severity: Moderate — CVSS 5.4 (CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:L/I:L/A:N). Weakness: CWE-79.
Affected Red Hat products: Migration Toolkit for Applications 8; Red Hat OpenShift AI (RHOAI); Red Hat OpenShift Container Platform 4. Under investigation: Red Hat Satellite 6.
Red Hat does not currently list a fixing RHSA for this CVE.
Is CVE-2026-59926 exploited?
No exploitation is reported in the sources VulniPulse tracks: CVE-2026-59926 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-2026-59926?
Upgrade to a fixed release named by Red Hat:
- 3.2.1
Confirm against the vendor advisory before you patch.
- < 3.2.1
Official advisory · high-confidence parse· fetched 11 days ago·verify at source
Mitigation checklist
- To mitigate this issue, avoid processing untrusted or unvalidated Markdown content with affected versions of the Mistune library. Implement robust input validation and sanitization for any user-provided Markdown before rendering to prevent the injection of malicious attributes or scripts.
Official advisory · high-confidence parse· fetched 11 days ago·verify at source
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