CVE-2026-59711

MEDIUM 6.1

showdown - Cross-Site Scripting via Unescaped Metadata Title in completeHTMLDocument

CVSS Score

6.1

EPSS Score

0.2%

EPSS Percentile

9th

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.

CWE	CWE-79
Vendor	showdown
Product	showdown
Published	Jul 6, 2026
Last Updated	Jul 7, 2026

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CVSS v3 Breakdown

CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N

Attack Vector

Network

Attack Complexity

Low

Privileges Required

None

User Interaction

Required

Scope

Changed

Confidentiality

Low

Integrity

Low

Availability

None

Affected Versions

showdown / showdown

0 ≤ 2.1.0

References

NVD ↗ CVE.org ↗ EPSS Data ↗

github.com: https://github.com/showdownjs/showdown/issues/1047 github.com: https://github.com/showdownjs/showdown vulncheck.com: https://www.vulncheck.com/advisories/showdown-cross-site-scripting-via-unescaped-metadata-title-in-completehtmldocument

Credits

🔍 Scott Moore - VulnCheck