CVE-2026-59926CWE-79

Mistune: XSS via unescaped class option in Admonition directive

Medium · published July 8, 2026

CVSS v4.0
5.3
EPSS
0%
Percentile
24.5
In the wild
Unconfirmed
What it is

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.

The record
Technical detail
CVSS v4.0
5.3 · MEDIUM
Vector
CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:P/VC:L/VI:L/VA:N/SC:L/SI:L/SA:N
EPSS
0.00327 · 24.5th percentile
Weakness
CWE-79 · Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting')
Published
2026-07-08T16:16Z
EPSS history
Timeline
  • 08 JUL 16:16Z
    Mistune: XSS via unescaped class option in Admonition directive
    cvelistv5