@nuxtjs/mdc's URL sanitizer misses SVG xlink:href and data:text/html, allowing XSS from untrusted markdown at the default configuration

Exploitation

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

CVSS

8.1 · CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:N

EPSS

• CVE-2026-63671: 0.47% estimated exploitation activity in the next 30 days; percentile 41.02 (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.

Summary @nuxtjs/mdc renders untrusted markdown (including raw HTML) to a Vue component tree. Across two prior advisories it added a URL/attribute sanitizer to block dangerous links in that HTML: validateProps / validateProp and an unsafeLinkPrefix deny-list (dist/runtime/parser/utils/props.js). The sanitizer runs at parse time (dist/runtime/parser/compiler.js) and parseMarkdown enables raw HTML by default (allowDangerousHtml: true, dist/runtime/parser/options.js), so the sanitizer is the only barrier and it applies with no configuration required. Two sibling vectors bypass that sanitizer at the default configuration: 1. SVG anchor xlink:href. validateProp only scheme-checks attributes named exactly href or src: An xlink:href (parsed to the hast property xLinkHref) is neither, so a javascript: URL on an SVG <a is passed through. The renderer maps the property back to the real attribute (MDCRenderer.vue: find(html, "xLinkHref").attribute is xlink:href), so the output element is <a…

Published by the source

16 Sep 2026, 22:14 UTC

Last modified by the source

16 Sep 2026, 22:30 UTC

Source last checked

26 Oct 2026, 13:02 UTC

1. Revision 3 · amended · 26 Oct 2026

   Amended from ghsa record GHSA-mxm6-v9r6-r94c

2. Revision 2 · amended · 24 Oct 2026

   Amended from osv record GHSA-mxm6-v9r6-r94c

3. Revision 1 · created · 23 Oct 2026

   Published from ghsa record GHSA-mxm6-v9r6-r94c

Preview the exact text before you copy it. Commands are read-only suggestions; review them before running anything.

# Patch Next advisory brief: CVE-2026-63671

Advisory: @nuxtjs/mdc's URL sanitizer misses SVG xlink:href and data:text/html, allowing XSS from untrusted markdown at the default configuration
IDs: CVE-2026-63671, GHSA-mxm6-v9r6-r94c
Record: https://patchnext.com/advisories/cve-2026-63671 (revision 3, source checked 26 Oct 2026, 13:02 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: High (CVSS 8.1)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: @nuxtjs/mdc 0.22.1. A vendor fix does not mean a deployment is fixed.

## Affected components
- npm @nuxtjs/mdc: affected < 0.22.1; fixed in 0.22.1

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

## Supported action
Upgrade each affected component to a fixed version on its release line. For a transitive dependency, upgrade the parent package or add an override or constraint, then regenerate the lockfile. Redeploy every environment that ran an affected version.

## Required regression checks
- Run the test suite and a production build.
- Exercise the features that depend on @nuxtjs/mdc.
- 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://github.com/advisories/GHSA-mxm6-v9r6-r94c (GitHub-reviewed advisory GHSA-mxm6-v9r6-r94c lists affected ranges: npm @nuxtjs/mdc >=0 <0.22.1)
- Verified: https://osv.dev/vulnerability/GHSA-mxm6-v9r6-r94c (OSV record GHSA-mxm6-v9r6-r94c lists affected ranges: npm @nuxtjs/mdc >=0 <0.22.1 (fixed))

Commands are suggestions: review each one before running it.