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CVE-2026-59711— showdown - Cross-Site Scripting via Unescaped Metadata Title in completeHTMLDocument

CVSS 6.1 · Medium EPSS 0.19% · P9

Possible ATT&CK Techniques 1AI

T1189 · Drive-by Compromise

Affected Version Matrix 1

VendorProductVersion RangeStatus
showdownshowdown≤ 2.1.0affected
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I. Basic Information for CVE-2026-59711

Vulnerability Information
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Vulnerability Title
showdown - Cross-Site Scripting via Unescaped Metadata Title in completeHTMLDocument
Source: NVD (National Vulnerability Database)
Vulnerability Description
showdown contains a cross-site scripting vulnerability in metadata title handling that allows attackers to inject arbitrary HTML and JavaScript. When completeHTMLDocument option is enabled, unescaped less-than and greater-than characters in markdown frontmatter metadata are inserted directly into HTML title tags, enabling attackers to break out of the title context and execute malicious scripts in the rendered page.
Source: NVD (National Vulnerability Database)
CVSS Information
CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N
Source: NVD (National Vulnerability Database)
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: NVD (National Vulnerability Database)
Vulnerability Title
ShowdownJS Showdown 跨站脚本漏洞
Source: CNNVD (China National Vulnerability Database)
Vulnerability Description
ShowdownJS Showdown是ShowdownJS团队开源的一个 JavaScript Markdown 到 HTML 转换器。 ShowdownJS Showdown 2.1.0及之前版本存在跨站脚本漏洞，该漏洞源于元数据标题处理存在跨站脚本漏洞，在启用completeHTMLDocument选项时，Markdown前置元数据中未转义的小于号和大于号字符被直接插入HTML标题标签，导致攻击者可跳出标题环境并注入任意HTML和JavaScript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

VendorProductAffected VersionsCPESubscribe
showdownshowdown 0 ~ 2.1.0 -

II. Public POCs for CVE-2026-59711

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III. Intelligence Information for CVE-2026-59711

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Proof of Concept for CVE-2026-59711 (1)

News Coverage for CVE-2026-59711 (1)

Other References for CVE-2026-59711 (1)

IV. Related Vulnerabilities

Same product: showdown
Same vendor: showdown
Same weakness: CWE-79

V. Comments for CVE-2026-59711

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