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

Quick assessment

Affected
lepture mistune
Exploitation
No confirmed in-the-wild exploitation; assess based on exposure
Recommended action
Check the vendor advisory and references for a fixed version. If immediate upgrade is impossible, restrict exposure and increase monitoring.

Hsiaoming Yang mistune是日本Hsiaoming Yang个人开发者的一个快速、可扩展的Markdown解析器。 Hsiaoming Yang mistune 3.2.1之前版本存在跨站脚本漏洞，该漏洞源于render_admonition()函数在拼接Admonition指令:class:选项到HTML class属性时未进行转义，允许属性注入和跨站脚本攻击。

AI Predicted 7.5 Difficulty: Easy EPSS 0.33% · P24

Possible ATT&CK Techniques 1 AI

T1189 · Drive-by Compromise

Affected Version Matrix 1

VendorProduct Version RangeStatus
lepture mistune < 3.2.1 affected
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I. Basic Information for CVE-2026-59926

Vulnerability Information
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Vulnerability Title
Mistune: XSS via unescaped class option in Admonition directive
Source: CVE Program / CVE List V5
Vulnerability 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.
Source: CVE Program / CVE List V5
CVSS Information
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
Source: CVE Program / CVE List V5
Vulnerability Type
在Web页面生成时对输入的转义处理不恰当(跨站脚本)
Source: CVE Program / CVE List V5
Vulnerability Title
Hsiaoming Yang mistune 跨站脚本漏洞
Source: CNNVD (China National Vulnerability Database)
Vulnerability Description
Hsiaoming Yang mistune是日本Hsiaoming Yang个人开发者的一个快速、可扩展的Markdown解析器。 Hsiaoming Yang mistune 3.2.1之前版本存在跨站脚本漏洞，该漏洞源于render_admonition()函数在拼接Admonition指令:class:选项到HTML class属性时未进行转义，允许属性注入和跨站脚本攻击。
Source: CNNVD (China National Vulnerability Database)
CVSS Information
N/A
Source: CNNVD (China National Vulnerability Database)
Vulnerability Type
N/A
Source: CNNVD (China National Vulnerability Database)

Affected Products

Vendor Product Affected Versions CPE Subscribe
lepture mistune < 3.2.1 -

II. Public POCs for CVE-2026-59926

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III. Intelligence Information for CVE-2026-59926

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Patches & Fixes for CVE-2026-59926 (1)

Vendor Advisories for CVE-2026-59926 (1)

Vendor Pages for CVE-2026-59926 (1)

Same Patch Batch · lepture · 2026-07-08 · 9 CVEs total

CVE-2026-59922 7.5 HIGH Mistune plugins/formatting: quadratic-time parsing on long runs of `~~x~~`, `==x==`, and `
CVE-2026-59925 7.5 HIGH inline_parser: quadratic-time parsing on long runs of `**x**` and `***x***` emphasis pairs
CVE-2026-59928 7.5 HIGH Mistune block_parser: quadratic-time parsing on long lists of repeated reference-link defi
CVE-2026-59923 6.1 MEDIUM Mistune: XSS via percent-encoded javascript URI bypass in safe_url()
CVE-2026-59929 6.1 MEDIUM Mistune renderers/html.safe_url: HARMFUL_PROTOCOLS list misses legacy and chained schemes
CVE-2026-59924 5.9 MEDIUM Mistune: Arbitrary File Read via Include directive path traversal
CVE-2026-59927 5.3 MEDIUM Mistune directives/include: mutual `.. include::` recursion crashes the renderer with `Rec
CVE-2026-59930 4.3 MEDIUM Mistune toc / TableOfContents directive: heading IDs use predictable `toc_N` numbering wit

IV. Related Vulnerabilities

Same product: mistune
Same vendor: lepture
Same weakness: CWE-79

V. Comments for CVE-2026-59926

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