Two defense-in-depth layers close the P1 in issue #304, where any browser
tab on the machine could fetch /live.js, extract the embedded token, and
drive every token-gated route.
1. Loopback-restricted CORS. The shared handler replaced its wildcard
`Access-Control-Allow-Origin: *` with reflection gated on a strict
isLoopbackOrigin() that URL-parses the Origin (so localhost.evil.com and
127.0.0.1.evil.com fail) and accepts only http/https on localhost,
127.0.0.1, or [::1]. Reflection always pairs with `Vary: Origin` so a
cache never hands one origin's authorized response to another. Remote
origins get no ACAO header; origin-less callers (script tags, curl, the
agent's own fetches) are unaffected.
2. Token-gated /live.js. The handler now 401s unless `?token=` matches
state.token, so the bundle (which embeds the token) is no longer served
to unauthenticated local pages. The injected <script src> carries the
token: live.mjs passes --token to live-inject.mjs, which threads it
through every injection path (HTML/JSX tag, Nuxt plugin, SvelteKit root
component) via a shared buildLiveScriptSrc(). The token stays optional in
live-inject so static fixture tests keep their bare src.
Tests: new live-server integration cases for the 401 gate, remote-origin
denial, loopback reflection + Vary, and token-guarded routes under a
loopback Origin; e2e session harness now injects with the token.
Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Paul BakausandClaude Fable 5
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