Medium [CVE-2026-59923] Arbitrary code execution through crafted Markdown links
This medium-severity Red Hat Linux advisory covers CVE-2026-59923 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 3.3.0, HTMLRenderer.safe_url() does not block percent-encoded javascript URIs, allowing attacker-supplied Markdown links or images to bypass URL protections and execute script in rendered HTML.
This issue is fixed in version 3.3.0. This can lead to the execution of arbitrary scripts in the rendered HTML, potentially compromising the user's system.
Red Hat products ship python-mistune in both the older 0.8.x series and newer 3.x series. The URL sanitization bypass applies to both versions: the 0.8.x escape_link() function and the 3.x safe_url() function both fail to decode percent-encoded characters before checking for dangerous URI schemes.
Exploitation requires an attacker who can inject Markdown content into an application that renders it with mistune, and a victim who clicks the malicious link. This limits the exposure.
Red Hat severity: Moderate — CVSS 6.1 (CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/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. Red Hat lists Red Hat Satellite 6 as not affected.
Red Hat does not currently list a fixing RHSA for this CVE.
Is CVE-2026-59923 exploited?
No exploitation is reported in the sources VulniPulse tracks: CVE-2026-59923 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-2026-59923?
Upgrade to a fixed release named by Red Hat:
- 3.3.0
Confirm against the vendor advisory before you patch.
- < 3.3.0
Official advisory · high-confidence parse· fetched 11 days ago·verify at source
Mitigation checklist
- Applications that render user-supplied Markdown with mistune can pass the HTML output through a dedicated HTML sanitizer such as bleach or nh3 before serving it to users. This removes dangerous URI schemes regardless of encoding.
Official advisory · high-confidence parse· fetched 11 days ago·verify at source
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