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.
Android app · Google Play
Monitor future Red Hat Linux CVEs from your phone.
Choose a whole vendor or a precise platform, then receive matching security advisories by phone notification, email, or both. Coverage follows 32 official vendor sources and 160+ reviewed platform categories.
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.
- < 3.3.0
Official advisory · high-confidence parse· fetched 10 days ago·verify at source
Mitigation checklist
- 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 10 days ago·verify at source
Discussion(0)
No comments yet. Share field notes, upgrade gotchas, or questions — verify against the vendor advisory before acting on community advice.
Sign in to join the discussion.