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](https://github.com/nuxt/nuxt/pull/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`](https://github.com/nuxt/nuxt/commit/2cce6fb02e621196d56df92e05594e07469b5a6d) - 3.x: commit [`1f2dd5e7`](https://github.com/nuxt/nuxt/commit/1f2dd5e78c77576437138e97671965573c232835) - `navigateTo({ open })` script-protocol guard: - 4.x: [#35206](https://github.com/nuxt/nuxt/pull/35206) (commit [`3394716d`](https://github.com/nuxt/nuxt/commit/3394716d4a913cba904b028df5338f2aead50032)) - 3.x: commit [`62fc32ed`](https://github.com/nuxt/nuxt/commit/62fc32eddf648b00a3890141e0235d2a222b024d) - Protocol-relative bypass in `reloadNuxtApp`: - 4.x: commit [`e447a793`](https://github.com/nuxt/nuxt/commit/e447a793c47766834f7497f8412a76cd56fd8ee1) - 3.x: commit [`6497d99d`](https://github.com/nuxt/nuxt/commit/6497d99dd106254abd089f6a263d7773869a343b) ### 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](https://github.com/alcls01111) via GitHub's coordinated disclosure flow (`GHSA-w7fp-2cfv-4837`), closed as a duplicate of this advisory.

Quoted source text, attributed separately from HOL analysis.