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TI-2026-42734 Aliases CVE-2026-59926GHSA-g97x-gvcm-x72h

Mistune: XSS via unescaped class option in Admonition directive

Priority LOW 24CWE-79Published · Updated

Key facts

Attack vector
Network
Privileges required
None
User interaction
Passive
Attack complexity
Low
Attack requirements
None
Impact type
Cross-site scripting
Confidentiality · integrity · availability
Low · Low · None
Fix status
Partial Red Hat: 4 without a fix

Attack profile from CVSS 4.0 · CNA. Fix status from CNA, GitHub and Red Hat. Impact type from CWE-79.

Summary

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.

Why it matters now

Exploitation None reported CISA SSVC · not in CISA KEV
EPSS 0.00327 25th percentileScored 2026-11-07
Fix Partial mistune (lepture): 3.2.1mistune (PyPI): 3.3.0Red Hat: 4 without a fix

SSVC decision points

CISA ADP · SSVC 2.0.3

Exploitation
None
Automatable
No
Technical impact
Partial

The decision (Track, Attend, Act) also depends on your mission and well-being impact; see CISA's SSVC guide.

Affected products

VendorProductAffected versionsFixed inStatusSource
lepturemistunebefore 3.2.13.2.1Patch availableCNA
—mistune (PyPI)before 3.3.03.3.0Patch availableGHSA-g97x-gvcm-x72h
  • mistune Vendorlepture Affected before 3.2.1 Fixed in 3.2.1 Patch available CNA
  • mistune (PyPI) Vendor— Affected before 3.3.0 Fixed in 3.3.0 Patch available GHSA-g97x-gvcm-x72h

CPE configurations NVD · 1

CPEVersionsRoleVendor
cpe:2.3:a:mistune_project:mistune:*:*:*:*:*:*:*:*before 3.3.0Vulnerablelepture
  • cpe:2.3:a:mistune_project:mistune:*:*:*:*:*:*:*:* Versions before 3.3.0 Vulnerable ·lepture

Remediation

  • Fix · CNA mistune (lepture) Fixed in 3.2.1
  • Fix · GHSA-g97x-gvcm-x72h mistune (PyPI) Fixed in 3.3.0 Advisory →

Vendor assessments

Red Hat

Red Hat rating: Moderate. Red Hat's page for this CVE →

ProductStatusPlan or fix
Migration Toolkit for Applications 8AffectedNo fix yet: Fix deferred
Red Hat OpenShift AI (RHOAI)AffectedNo fix yet: Fix deferred
Red Hat OpenShift Container Platform 4AffectedNo fix yet: Fix deferred
Red Hat Satellite 6Affected—

Timeline

  1. 2026-10-02 Threatist record created from CVE-2026-59926
  2. 2026-10-03 Alias added: GHSA-g97x-gvcm-x72h

References

Patch 1

Advisory 2

Other 3

  • TI-2026-42736 Mistune block_parser: quadratic-time parsing on long lists of repeated reference-link definitions CVSS 3.1HIGH 7.5
  • TI-2026-42730 Regular expression denial of service in lepture mistune CVSS 3.1HIGH 7.5
  • TI-2026-42731 Mistune: XSS via percent-encoded javascript URI bypass in safe_url() CVSS 3.1MEDIUM 6.1
  • TI-2026-32774 Mistune Image Directive CSS Injection Vulnerability CVSS 3.1MEDIUM 6.1
  • TI-2026-32773 Mistune TOC Anchor Injection XSS CVSS 3.1MEDIUM 6.1
  • TI-2026-32595 Mistune Math Plugin XSS Escape Bypass CVSS 3.1MEDIUM 6.1
See all 16 →

Sources

This product uses the NVD API but is not endorsed or certified by the NVD. Sources and licences