Nuxt: Reflected XSS in `<NuxtLink>` via unsanitised `javascript:` or `data:` URL

Summary

<NuxtLink> did not validate the URL scheme of values bound to its to or href props before rendering them into the href attribute of the underlying <a> element. When an application binds attacker-controlled input (a query parameter, a CMS field, a user-supplied profile URL) to <NuxtLink :to> or :href, the attacker can supply a javascript: or vbscript: URL that is reflected verbatim into the rendered markup. Clicking the link executes the supplied script in the origin of the Nuxt application, resulting in reflected DOM-based cross-site scripting. A data:text/html,... payload reflected through the same sink does not execute in the application's origin but enables a same-tab phishing surface anchored to a legitimate application link.

The same value was exposed to consumers of the component's custom slot via the href and route.href props, so applications that re-bind those values to their own anchors were affected identically.

Unlike the previously reported navigateTo issue (CVE-2024-34343), the sink here is the rendered anchor itself; the existing isScriptProtocol checks in navigateTo and reloadNuxtApp are not on the code path. The onClick handler intentionally returns early for external links so the browser's native protocol-based navigation runs.

Affected component

• File: packages/nuxt/src/app/components/nuxt-link.ts
• Sink: h('a', { href: href.value, ... }) in the default render, plus the href / route.href props passed to the custom slot.
• Broken check: external auto-detection treated any hasProtocol(path, { acceptRelative: true }) value as an "external link", then rendered the value directly as <a href> without rejecting script-capable protocols. There was no equivalent of the navigateTo isScriptProtocol(protocol) gate in this path.

Impact

Any Nuxt application that binds user-controlled values to <NuxtLink :to> / :href was vulnerable. Common shapes: profile-link rendering (<NuxtLink :to="user.website">), "share this" / "open in new tab" handlers that pass through a query parameter, CMS-driven landing pages that render <NuxtLink :to="cms.cta.url">, and marketplace listings that show seller-supplied links.

For javascript: / vbscript: the primitive is reflected XSS in the application's first-party origin (session theft for non-HttpOnly cookies, CSRF token theft, account takeover via DOM rewriting, credential harvesting via fake login overlays). For data:text/html,... the attacker gets a same-tab phishing surface anchored to a legitimate application link.

Patches

Fixed in nuxt@4.4.7 (commit `0103ce06`) and backported to nuxt@3.21.7 (commit `53284043`). The fix sanitises the resolved external href before it is passed to <a> or the custom slot: control characters and whitespace are stripped, leading view-source: prefixes are unwrapped, and any remaining script-capable scheme (per isScriptProtocol) causes the href to be replaced with an empty string.

Workarounds

Until you can upgrade, validate URLs at the source before binding them to <NuxtLink :to> / :href. For example, only accept paths that start with / (and not //), or run user-supplied URLs through new URL(value) and reject anything whose protocol is not in an allow-list (typically http: and https:).