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CVE-2026-63671 high CVSS 8.1

Cross-Site Scripting (XSS) in @nuxtjs/mdc (CVE-2026-63671)

Summary

Cross-site scripting in @nuxtjs/mdc (CVE-2026-63671). Confidential information can be exposed externally. Exploitable via validateProps. Mitigation: upgrade to 0.22.1 or later.

Original description

The description as published by the source.

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:

    if (attribute === "href" || attribute === "src") return isAnchorLinkAllowed(value);
return true;

    An xlink:href (parsed to the hast property xLinkHref) is neither, so a javascript: URL on an SVG 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. Clicking it runs the script in the page origin. Plain `` is correctly stripped, which is what makes this the un-patched sibling.

  2. ``. data:text/html is present in unsafeLinkPrefix, but the check compares it against url.protocol:

    if (unsafeLinkPrefix.some((prefix) => url.protocol.toLowerCase().startsWith(prefix))) retu…

Source: NIST National Vulnerability Database NVD GitHub Advisory

Auto-generated summary

Assembled by SecPulse from the source data (CVSS, CWE, affected versions) using templates — no AI involved. Check the original description and references below for exact details.

A vulnerability tracked as CVE-2026-63671 has been found in @nuxtjs/mdc.
Attackers can target a specific entry point like validateProps over the network to misuse the product.
Confidential information can be exposed externally. CVSS score: 8.1/10.
What to do: upgrade @nuxtjs/mdc to 0.22.1 or later.
If unsure, ask your IT team or search "@nuxtjs/mdc CVE-2026-63671" on the vendor's site.

CVE-2026-63671 (@nuxtjs/mdc) — CWE-79 / CVSS v3 8.1
Attack vector: remote (network-reachable) / unauthenticated
Attack surface: validateProps / validateProp / unsafeLinkPrefix / parseMarkdown
Patched: 0.22.1 — apply immediately
Plan: 1) Audit SBOM/dependencies, 2) Stage→prod upgrade, 3) Add WAF/proxy monitoring on affected endpoints, 4) Hunt IOCs in logs.
Refs: see the GHSA / vendor advisory / patched release linked on this page.

❓ What is the problem

Cross-site scripting (XSS) (CWE-79) exists in @nuxtjs/mdc. Attackers reach the vulnerable code path via validateProps without authentication.

📍 Affected scope

Check the vendor advisory for the affected versions of @nuxtjs/mdc. Attack surface: validateProps / validateProp / unsafeLinkPrefix / parseMarkdown.

🔥 Severity

Severity: High (CVSS 8.1/10). Confidential information can be exposed externally.

🔧 How to fix

Update to 0.22.1.

🛡️ Workaround

Until the patch is applied: disable the affected feature, apply WAF rules, or restrict access via network ACLs.

🔍 Detection

Search webserver/proxy logs for unusual request patterns matching this CVE's known IOCs. Run grep -r '@nuxtjs/mdc' . against your dependency files (package-lock.json, requirements.txt, go.sum) to find affected services.

Response actions

Concrete steps and command examples for SOC/SRE teams to execute in order

  1. 1
    Identify exposure identify 
    grep -r '@nuxtjs/mdc' . | grep -v node_modules

    リポジトリと本番環境の依存ファイル (package-lock.json / requirements.txt / go.sum / Gemfile.lock 等) で @nuxtjs/mdc を grep し、稼働しているサービス・バージョンを把握する。

  2. 2
    Apply patch patch 
    Upgrade @nuxtjs/mdc to 0.22.1

    ステージング環境で 0.22.1 に上げて回帰テスト → 本番反映。回帰テストはアプリの主要ハッピーパスを含めること。

  3. 3
    Post-deployment verification verify 
    Confirm patched version is live in production

    パッチ適用後、ステージングで PoC または同等の悪用パターンを再現して脆弱性が閉じたことを確認。本番ではアクセスログ・WAF でアラート再発が無いか継続監視。

Affected packages

npm @nuxtjs/mdc
[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"fixed":"0.22.1"}]}]

References

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