showdown metadata title handling allows cross-site scripting

Exploitation

No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.

CVSS 4.0

5.3 · CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:P/VC:L/VI:L/VA:N/SC:L/SI:L/SA:N · score source

EPSS

• CVE-2026-59711: 0.23% estimated exploitation activity in the next 30 days; percentile 13.89 (FIRST EPSS, 2026-11-03). This is a model estimate, not proof of exploitation or customer exposure.

As published by the source; long descriptions are shortened.

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.

Published by the source

6 Jul 2026, 21:30 UTC

Last modified by the source

10 Sep 2026, 03:51 UTC

Source last checked

26 Oct 2026, 13:01 UTC

1. Revision 3 · amended · 26 Oct 2026

   Amended from ghsa record GHSA-cr32-g25g-vxjj

2. Revision 2 · amended · 24 Oct 2026

   Reviewed OSV alias/range/CVSS4 correction; package source scopes and original publication preserved. No customer finding resolved.

3. Revision 1 · created · 24 Oct 2026

   Published from osv record GHSA-cr32-g25g-vxjj

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# Patch Next advisory brief: CVE-2026-59711

Advisory: showdown metadata title handling allows cross-site scripting
IDs: CVE-2026-59711, GHSA-cr32-g25g-vxjj
Record: https://patchnext.com/advisories/cve-2026-59711 (revision 3, source checked 26 Oct 2026, 13:01 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: Medium (CVSS 5.3)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor response not established. A vendor fix does not mean a deployment is fixed.

## Affected components
- npm showdown: affected <= 2.1.0

## Suggested inspection (read-only)
- `npm ls showdown --all`: lists every installed copy and version, including transitive ones. Run in the project root after `npm ci`.

## Supported action
No complete vendor fix is recorded. Follow the primary source's mitigation guidance and check this record again before closing anything.

## Required regression checks
- Run the test suite and a production build.
- Exercise the features that depend on showdown.
- Repeat the inspection and confirm that only fixed versions remain installed.

## Rollback considerations
- Keep the previous lockfile and deployment artifact. Rolling back reinstates the vulnerable version, so apply any documented mitigation while you fix forward.

## Unresolved questions
- Which deployments run an affected version?
- Exploitation status can change. Check again before lowering the priority.
- Mark the work resolved only after the fixed version is verified in production.

## Sources
- Verified: https://osv.dev/vulnerability/GHSA-cr32-g25g-vxjj (OSV record GHSA-cr32-g25g-vxjj lists affected ranges: npm showdown >=0 <=2.1.0)
- Verified: https://github.com/advisories/GHSA-cr32-g25g-vxjj (GitHub-reviewed advisory GHSA-cr32-g25g-vxjj lists affected ranges: npm showdown >=0 <=2.1.0)

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