CVE-2026-59711

Summary

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.

Affected Software

Weaknesses

• CWE-79: Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting')

ADP Enrichment

CISA ADP Vulnrichment

• SSVC:
• Exploitation: poc
  • Automatable: no
  • Technical Impact: partial

Additional References

• https://github.com/showdownjs/showdown/issues/1047

References

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

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