How severe is CVE-2026-59926?

No CVSS score has been assigned to CVE-2026-59926 yet. Review the advisory details and affected package list to assess your exposure.

Which packages are affected by CVE-2026-59926?

CVE-2026-59926 affects the following packages: mistune (PyPI). Ecosystems affected: PyPI.

How do I fix CVE-2026-59926?

Update mistune to 3.3.0 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-59926 is resolved across your whole dependency graph.

How do I detect CVE-2026-59926 in my PyPI dependencies?

Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for mistune, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.

How do I mitigate CVE-2026-59926 if there is no patch (or I can't update yet)?

Escape or sanitise the affected output on the server side rather than relying on client-side filtering, and add a Content-Security-Policy that blocks inline script execution so injected markup cannot run even if it reaches the page.

Is CVE-2026-59926 actively exploited in the wild?

No public exploit code has been indexed for CVE-2026-59926 yet. This does not mean the vulnerability cannot be exploited — absence of public exploits does not imply safety. Apply the recommended fix and use O3 Security to monitor your exposure.

What is the EPSS score for CVE-2026-59926?

CVE-2026-59926 has an EPSS (Exploit Prediction Scoring System) score of 0.3%, placing it in the 24th percentile of all CVEs. EPSS is maintained by FIRST.org and estimates the probability that a vulnerability will be exploited in the wild within the next 30 days. This score indicates relatively lower exploitation probability, though the CVSS severity should still guide your patching priority.

What type of vulnerability is CVE-2026-59926?

CVE-2026-59926 is classified as Cross-site Scripting (XSS) (CWE-79). This weakness type describe the underlying flaw category, which helps determine the potential impact and the right class of mitigation. This is a high-impact weakness class that often enables remote code execution or data exposure.

When was CVE-2026-59926 published, and has it been updated?

CVE-2026-59926 was published on July 8, 2026 and was last updated on August 12, 2026. Advisory data evolves as severity scores, affected ranges, and exploit intelligence are revised — always check the latest version of the advisory before acting.

🐍 PyPI

Not in CISA KEV

CVE-2026-59926 — mistune

Fix: lepture/mistune@a3cb6e5

CVE-2026-59926 is a Cross-site Scripting (XSS) vulnerability in mistune. A fix is available for mistune — see the affected versions and patch details below.

Mistune: XSS via unescaped class option in Admonition directive

Also known asGHSA-g97x-gvcm-x72hPYSEC-2026-2214

Published

Jul 8, 2026

Updated

Aug 12, 2026

Affected

1 pkg

Patched

1 / 1

Exploits

None indexed

Exploitation data as of Oct 13, 2026 · OSV.dev, NVD, FIRST.org (EPSS)

Exploitation Status

No confirmed exploitation observed yet

CISA’s own triage has not observed active exploitation or public proof-of-concept code for this CVE as of its last assessment.

Exploitation and automatability from CISA’s SSVC triage for CVE-2026-59926.

EPSS Exploitation Probability

via FIRST.org ↗

0.3%probability of exploitation in next 30 days

Lower Risk0.00%

Lower risk than most CVEs24th percentile — riskier than 24% of all scored CVEsHighest risk

Probability of exploitation in the next 30 days, from FIRST.org EPSS.

Real-World Exposure

1 pkg affected

🐍mistune

Real-time download stats are indexed for npm and PyPI packages. This vulnerability affects PyPI packages — download data is not available via public APIs for these ecosystems.

Description

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.

Affected Packages

1 total 1 fixed

Ecosystem	Package	Vulnerable range	Fix
🐍PyPI	`mistune`	all versions	3.3.0`pip install --upgrade 'mistune==3.3.0'`

Affected Products

1 product · 1 configurations

Application

mistunemistune_project

< 3.3.0

range

Detection & mitigation playbook

Open-source dependency

Detect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for mistune, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update mistune to 3.3.0 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-59926 is resolved across your whole dependency graph.
Workarounds
Escape or sanitise the affected output on the server side rather than relying on client-side filtering, and add a Content-Security-Policy that blocks inline script execution so injected markup cannot run even if it reaches the page.

Fixing This On Your OS

If you run this on a Linux distribution, patch through your package manager against the distro's own security advisory below — it tracks the exact backported fix for your release, which can ship on a different timeline (and sometimes a different severity) than the upstream project.

Red HatModerate

This Moderate flaw in the Mistune Markdown parser allows for Cross-Site Scripting (XSS) due to improper sanitization of user-controlled input within the Admonition directive's class attribute. An attacker could exploit this by providing specially crafted Markdown content, leading to the execution of arbitrary script…

Workaround published by Red Hat

To mitigate this issue, avoid processing untrusted or unvalidated Markdown content with affected versions of the Mistune library. Implement robust input validation and sanitization for any user-provided Markdown before rendering to prevent the injection of malicious attributes or scripts.

Source: Red Hat security advisory for CVE-2026-59926 (CC BY 4.0)

Frequently Asked Questions

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