XSS in Showdown
CVE-2026-59711
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.
Vulnerability class: XSS (Cross-Site Scripting)
EPSS: 0.002 (8.7th percentile) — read the EPSS interpretation.
CVSS v3 metric
CVSS v3 base score 6.1 (Medium). Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N.
Affected products
- Showdown — versions 0
Weakness classification (CWE)
References
- disclosure@vulncheck.com (product)
- disclosure@vulncheck.com (issue-tracking)
- disclosure@vulncheck.com (third-party-advisory)
Frequently asked questions
- What is CVE-2026-59711?
- CVE-2026-59711 is a medium-severity vulnerability in Showdown, classified under Cross-site Scripting. CVSS score: 6.1/10. Published 2026-07-06.
- How severe is CVE-2026-59711?
- Medium severity. CVSS v3 base score is 6.1 out of 10.