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Advisory severityMedium6.1Red Hat Linux

Medium [CVE-2026-59929] Cross-site scripting via incomplete URL scheme filtering

This medium-severity Red Hat Linux advisory covers CVE-2026-59929 affecting Migration Toolkit for Applications 8, Red Hat OpenShift AI (RHOAI), Red Hat Satellite 6.

Aggregated and source-linked by VulniPulse. Data sources, validation and limitations.

CVE-2026-59929 Source published Source updated

VulniPulse record published Record updated

CVE-2026-59929
Affected products & platforms
Red Hat LinuxUnclassified
Open source advisory

Summary

Mistune is a Python Markdown parser with renderers and plugins.

Prior to 3.3.0, the safe_url filter in src/mistune/renderers/html.py blocks only javascript:, vbscript:, file:, and data: schemes, allowing legacy or chained schemes such as feed:, view-source:, jar:, livescript:, mocha:, ms-its:, mk:, and res: to reach rendered href and src attributes and potentially execute script in affected user agents.

This issue is fixed in version 3.3.0. The `safe_url` filter, intended to prevent malicious Uniform Resource Locators (URLs), did not adequately block all potentially harmful schemes.

This oversight allows an attacker to embed specially crafted URLs using legacy or chained schemes within rendered HTML attributes. Consequently, a remote attacker could exploit this to execute arbitrary script code in a user's browser, leading to a Cross-Site Scripting (XSS) vulnerability.

This Moderate-impact flaw in Mistune, a Python Markdown parser, allows for Cross-Site Scripting (XSS) due to insufficient filtering of URL schemes. Exploitation requires a user to process specially crafted Markdown content, which could lead to arbitrary script execution in the user browser.

Red Hat products that utilize Mistune to render untrusted Markdown input are susceptible to this vulnerability. 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.

Is CVE-2026-59929 exploited?

No exploitation is reported in the sources VulniPulse tracks: CVE-2026-59929 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-2026-59929?

Upgrade to a fixed release named by Red Hat:

  • 3.3.0

Confirm against the vendor advisory before you patch.

Affected versions
  • < 3.3.0

Official advisory · high-confidence parse· fetched 11 days ago·verify at source

Fixed versions
  • 3.3.0

Official advisory · high-confidence parse· fetched 11 days ago·verify at source

Mitigation checklist

Recommended fix / mitigation
  • No dedicated mitigation is available beyond upgrading to Mistune 3.3.0 or later, which fully blocks all dangerous URL schemes in the safe_url filter. As a temporary workaround, applications can wrap Mistune output in an additional allow-list-based URL sanitizer before rendering untrusted Markdown content, or avoid rendering Markdown from untrusted/attacker-controlled sources.

Official advisory · high-confidence parse· fetched 11 days ago·verify at source

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