Bug 2498149 (CVE-2026-59926)

Summary: CVE-2026-59926 mistune: Mistune: Cross-Site Scripting via unescaped HTML class attribute in Admonition directive
Product: [Other] Security Response Reporter: OSIDB Bzimport <bzimport>
Component: vulnerabilityAssignee: Product Security <prodsec-ir-bot>
Status: NEW --- QA Contact:
Severity: medium Docs Contact:
Priority: medium    
Version: unspecifiedCC: anthomas, ehelms, ggainey, jpasqual, juwatts, mhulan, nmoumoul, osousa, pcreech, rchan, rjohnson, smallamp, tmalecek
Target Milestone: ---Keywords: Security
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Hardware: All   
OS: Linux   
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A flaw was found in Mistune, a Python Markdown parser. The `render_admonition()` function in the Admonition directive concatenates user-controlled input into the HTML class attribute without proper escaping. This vulnerability allows for attribute injection and Cross-Site Scripting (XSS) attacks, even when the HTMLRenderer escape mode is enabled. A remote attacker could exploit this by providing specially crafted input, leading to the execution of arbitrary script code in the user's browser.
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oVirt Team: --- RHEL 7.3 requirements from Atomic Host:
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Description OSIDB Bzimport 2026-07-08 17:02:05 UTC
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.