CVE-2026-59711
Official description Straight from the sourceThe vendor's or NVD's own wording, published unedited. Authoritative, but often terse — it says what broke, rarely what to do.
NVD · uneditedshowdown 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.
Technical summary Written by usOur analysis, written from the advisory, the CVSS vector and the affected-version data. It adds context the advisory leaves out, and never invents facts that are not in the source.
dbcve analysis · moderate confidenceshowdown library fails to escape less-than and greater-than characters from markdown frontmatter metadata when the completeHTMLDocument option is enabled. This allows attackers to inject malicious HTML/script tags by breaking out of the HTML title element context.
Verify against the referenced sources before acting — the references below are authoritative for this CVE, this summary is not.
CVSS breakdown How the score is builtThe industry scoring standard. It rates how the flaw is reached, what it takes to exploit, and what an attacker gains — the score is derived from those, not the other way round.
From the vector- Attack vector
- Network
- Complexity
- Low
- Privileges
- None
- User interaction
- Required
- Scope
- Changed
- Confidentiality
- Low
- Integrity
- Low
- Availability
- None
CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N
Am I affected? How to checkSteps we derive from the advisory and the affected-version data, so you can decide whether this CVE reaches your setup. They are a guide, not a scan — your own configuration is the authority.
dbcve checksWork through these to decide whether this CVE applies to you.
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Identify showdown library versionRun 'npm list showdown' or check package.json to find the installed showdown version. If using a bundled library, inspect the library file for version string or check the loaded library version programmatically.Affected if The installed version is unpatched and within the vulnerable range (all versions before the security fix)
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Verify completeHTMLDocument option is enabledSearch your codebase for showdown configuration where the converter is initialized. Look for instances of 'completeHTMLDocument: true' or 'completeHTMLDocument: 1' in the options object passed to showdown.Affected if The completeHTMLDocument option is set to true or enabled in the showdown configuration
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Confirm frontmatter metadata is processedExamine your markdown input files for frontmatter blocks (content between --- delimiters at the top of the file). Verify that your application passes markdown containing frontmatter to showdown for conversion.Affected if Your markdown files contain frontmatter metadata and this content is processed by showdown with completeHTMLDocument enabled
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Inspect HTML output for unescaped characters in title tagRender a sample markdown file with frontmatter through showdown with completeHTMLDocument enabled. Open the generated HTML and locate the <title> element in the <head> section. Check if raw < or > characters appear unescaped (should be < and >).Affected if The generated HTML <title> tag contains unescaped < or > characters that could break out of the title element context
You are affected if you use a vulnerable version of showdown with the completeHTMLDocument option enabled while processing markdown that contains frontmatter metadata with unescaped HTML special characters.
Generated from the published advisory. Verify against your own configuration.
Remediation Closing itWhat it takes to close this. Where a vendor fix exists we point at it; where none exists we say so plainly, and can build one. Effort estimates are scoped from the advisory, not from your codebase.
From vendor dataEscape special HTML characters (<, >, &, ", ') in frontmatter metadata before inserting into the document title tag, or implement input validation to reject metadata containing unescaped HTML special characters when completeHTMLDocument is enabled.
- Consultation2.0 h
- Implementation4.0 h
- Testing3.0 h
- Review / QA2.0 h
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Free · runs locallyCheck whether your project pulls in CVE-2026-59711 — or any other known-vulnerable package — straight from your lock files. Free and open source; it runs locally and uploads nothing.
References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.
Primary sourcesPractitioner notes
ContributedPeer-ranked notes from engineers who’ve handled CVE-2026-59711 in production — separate from our analysis above.
The advisory tells you what broke. It rarely tells you what actually worked. If you’ve dealt with this one, that detail is what the next engineer is searching for.
- The version that genuinely resolved it — not the one the vendor claimed
- A config change or rule that shut the vector down
- A gotcha in the upgrade path that cost you an afternoon
No notes yet
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- Version or environment caveats, and links to real fixes
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