CVE-2026-59926: Mistune: XSS via unescaped class option in Admonition directive

mediumCVSS 6.1CVE-2026-59926

CSIRTS triage

vendor: Mistune product: Mistune Cross-site scripting

What: An XSS vulnerability exists via unescaped class option in the Admonition directive.
Who is affected: Users of Mistune are affected.
Urgency: Remediation is medium due to the medium severity of the vulnerability.
Action: Update to the latest version of Mistune.

AI-assisted analysis generated from the source advisory — verify against the original.

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Details

Source: Microsoft Security Response Center (INTL · vendor-psirt · site)
Severity: medium — CVSS 6.1
Published: 2026-07-02
Exploitation: Not in CISA KEV at last sync

Original advisory: https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-59926

Exploitation outlook

EPSS (FIRST.org) estimates each CVE’s probability of exploitation in the next 30 days — here is the CSIRTS.com read on those numbers.

Low exploitation riskCVE-2026-599260.19% 30-day exploitation probability — currently an unlikely target, but scores change as exploit code circulates. Riskier than 9% of all scored CVEs.

Referenced CVEs

CVE	CSIRTS overview	External
CVE-2026-59926	coverage & exploitation status	NVD · CVE.org

Same CVEs, other sources

How other CERTs, PSIRTs and databases cover the vulnerabilities in this advisory.

mediumCVE-2026-59926: Mistune is a Python Markdown parser with renderers and plugins. Prior to 3.2.1, render_admonit…nvd

Recent advisories for Mistune

A cluster of recent advisories against the same product widens the attack surface — attackers routinely chain freshly published CVEs on one product, so review these together.

highGHSA-qcq2-496w-v96p: Mistune: Potential DoS via quadratic-time parsing in parse_link_textghsa · 2026-07-09
mediumCVE-2026-59930: Mistune is a Python Markdown parser with renderers and plugins. Prior to 3.3.0, the toc plugin…nvd · 2026-07-08
mediumCVE-2026-59929: Mistune is a Python Markdown parser with renderers and plugins. Prior to 3.3.0, the safe_url f…nvd · 2026-07-08
highCVE-2026-59928: Mistune is a Python Markdown parser with renderers and plugins. Prior to 3.3.0, a Markdown doc…nvd · 2026-07-08
mediumCVE-2026-59927: Mistune is a Python Markdown parser with renderers and plugins. Prior to 3.3.0, the Include di…nvd · 2026-07-08
mediumCVE-2026-59926: Mistune is a Python Markdown parser with renderers and plugins. Prior to 3.2.1, render_admonit…nvd · 2026-07-08