Nuxt: URL-handling weaknesses in `navigateTo` and `reloadNuxtApp`: SSR open redirect, client-side script execution via the `open` option, and protocol-relative bypass in `reloadNuxtApp`

Summary

Three weaknesses in Nuxt's client-navigation URL handling, all reachable
from documented public APIs (navigateTo and reloadNuxtApp):

1. SSR open redirect in navigateTo via path-normalisation bypass.
   navigateTo decided whether a target was external by inspecting the raw
   input with hasProtocol(..., { acceptRelative: true }). Inputs such as
   /..//evil.com, /.//evil.com, /%2e%2e//evil.com, or
   /app/..//evil.com slipped past that check because they start with
   /, but WHATWG URL parsing then normalised them to the
   protocol-relative pathname //evil.com. The normalised value was
   written to the Location response header and into the
   <meta http-equiv="refresh"> body of the SSR redirect page, so a
   victim's browser would resolve the redirect cross-origin to the
   attacker's host.

2. Client-side script execution via navigateTo({ open: ... }). The
   client-side early-open handler called window.open(toPath, ...) without
   applying the isScriptProtocol check that gates the normal navigateTo
   path. A target of javascript:... (or another script-capable scheme)
   passed to navigateTo(url, { open: { ... } }) therefore executed in the
   application's origin instead of being rejected.

3. Open redirect in reloadNuxtApp via protocol-relative bypass.
   reloadNuxtApp({ path }) rejects script-capable protocols by parsing
   the path with new URL(path, window.location.href) and checking the
   resolved protocol against isScriptProtocol. Protocol-relative paths
   such as //evil.com resolve to the current page's protocol (https:),
   which passes that check; the value is then assigned to
   window.location.href, which the browser treats as a cross-origin
   redirect. This is the same protocol-relative bypass family as (1), in
   a different sink.

Impact

For (1), the practical risk is phishing or OAuth-code theft against any
Nuxt app that forwards user-controlled input (for example a ?next=
query parameter on a login route) into navigateTo on the server. The
framework documents that navigateTo blocks external hosts unless
external: true is passed, so maintainers commonly rely on it as the
safe path for post-login redirects.

For (2), any app that passes a user-controlled URL into
navigateTo(url, { open: { ... } }) was vulnerable to reflected XSS in
the application's first-party origin.

For (3), any app that forwards user-controlled input into
reloadNuxtApp({ path }) could be redirected cross-origin for phishing
or OAuth-code theft, even on releases that already shipped the
isScriptProtocol guard added by #35115.

Patches

Fixed in [email protected] and backported to [email protected]. The three sinks
are addressed by:

• Path-normalisation bypass in navigateTo:
• 4.x: commit 2cce6fb0
• 3.x: commit 1f2dd5e7
• navigateTo({ open }) script-protocol guard:
• 4.x: #35206 (commit 3394716d)
• 3.x: commit 62fc32ed
• Protocol-relative bypass in reloadNuxtApp:
• 4.x: commit e447a793
• 3.x: commit 6497d99d

Workarounds

• For (1): validate redirect targets before passing them to navigateTo,
  for example reject any input where
  new URL(target, 'http://localhost').pathname starts with //, or
  only accept a known allow-list of paths.
• For (2): reject any user-controlled URL whose protocol is not in an
  allow-list (typically just http: and https:) before passing it to
  navigateTo({ open: ... }).
• For (3): same shape as (1). Reject paths starting with // (or where
  new URL(path, window.location.href).host !== window.location.host)
  before passing to reloadNuxtApp({ path }).

References

• CWE-601: URL Redirection to Untrusted Site ('Open Redirect')
• CWE-79: Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting')

Credits

Reported by Anthropic / Claude as ANT-2026-S08HN6DH through Anthropic's
coordinated vulnerability disclosure programme.

The reloadNuxtApp protocol-relative bypass (sink 3) was independently
reported by @alcls01111 via GitHub's
coordinated disclosure flow (GHSA-w7fp-2cfv-4837), closed as a
duplicate of this advisory.