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)
Published · last modified .
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.
EPSS exploit prediction
EPSS: 0.003 (23.7th percentile), scored .
Very low probability of exploitation in the next 30 days; routine patching cadence is appropriate. 24th percentile — 23.7% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.
EPSS over last 30 days · oldest: 0.003 · newest: 0.003 · change: 0.000
Affected products
- Showdown — versions 0
Weakness classification (CWE)
References
- github.com/showdownjs/showdown (product)
- github.com/showdownjs/showdown/issues/1047 (issue-tracking)
- www.vulncheck.com/advisories/showdown-cross-site-scripting-via-unescaped-metada… (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.