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CVE-2026-59923— Mistune: XSS via percent-encoded javascript URI bypass in safe_url()

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 3.3.0之前版本存在跨站脚本漏洞，该漏洞源于HTMLRenderer.safe_url()未能阻止百分号编码的javascript URI，导致攻击者提供的Markdown链接或图片可绕过URL保护并在渲染的HTML中执行脚本。

CVSS 6.1 · Medium EPSS 0.35% · P27

Affected Version Matrix 1

VendorProduct Version RangeStatus
lepture mistune < 3.3.0 affected
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I. Basic Information for CVE-2026-59923

Vulnerability Information
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Vulnerability Title
Mistune: XSS via percent-encoded javascript URI bypass in safe_url()
Source: CVE Program / CVE List V5
Vulnerability Description
Mistune is a Python Markdown parser with renderers and plugins. Prior to 3.3.0, HTMLRenderer.safe_url() does not block percent-encoded javascript URIs, allowing attacker-supplied Markdown links or images to bypass URL protections and execute script in rendered HTML. This issue is fixed in version 3.3.0.
Source: CVE Program / CVE List V5
CVSS Information
CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A: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 3.3.0之前版本存在跨站脚本漏洞，该漏洞源于HTMLRenderer.safe_url()未能阻止百分号编码的javascript URI，导致攻击者提供的Markdown链接或图片可绕过URL保护并在渲染的HTML中执行脚本。
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 < 3.3.0 -

II. Public POCs for CVE-2026-59923

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III. Intelligence Information for CVE-2026-59923

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Patches & Fixes for CVE-2026-59923 (1)

Vendor Advisories for CVE-2026-59923 (1)

Vendor Pages for CVE-2026-59923 (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-2026-59929 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
CVE-2026-59926 Mistune: XSS via unescaped class option in Admonition directive

IV. Related Vulnerabilities

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

V. Comments for CVE-2026-59923

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