fix(server): apply the Host check before the app's own routes

Vite installs its Host check after the middleware plugins add in
configureServer, so the provider and /api routes answered any Host,
including a DNS-rebinding name. hostCheckPlugin runs first on the dev and
preview servers and applies Vite's rule with the same allowed hosts: IP
addresses, localhost and *.localhost, the configured server host, and the
listed names. A test drives a real Vite server with an unlisted Host.

Co-Authored-By: Claude Opus 5.5 <[email protected]>

CHANGELOG.md

@@ -2,6 +2,12 @@
 
 ## [Unreleased]
 
+- Apply the Host check before the app's own routes. Vite installs its Host
+  check after the middleware that plugins add, so the provider and `/api`
+  routes used to answer any Host, including a DNS-rebinding name, in every
+  mode. A first-running middleware now applies the same allowed hosts on the
+  dev and preview servers.
+
 - Refuse cross-site browser requests to the cost-bearing and log endpoints
   (`/api/realtime/token`, `/api/openai/hud-summary`,
   `/api/google/nearby-places`, `/api/realtime/debug-log`): a foreign or opaque

SECURITY.md

@@ -71,7 +71,7 @@ The data proxies under `server/providers/` are written so the browser cannot tur
 - **Sanitized errors** — internal error details are not echoed back to clients.
 - **Coalesced OAuth refresh** and cached successful responses only (OpenSky).
 - **Redacted debug logging.** The voice debug log (`.gev-logs/`, gitignored) strips API keys, bearer tokens, client secrets, and image data URLs before writing.
-- **Cross-site gate on cost/log endpoints.** The cost-bearing (`/api/realtime/token`, `/api/openai/hud-summary`, `/api/google/nearby-places`) and log (`/api/realtime/debug-log`) endpoints refuse cross-site browser requests: a foreign or opaque `Origin`, a `Sec-Fetch-Site` other than `same-origin`/`none` (this is what blocks an `<img>`/navigation that carries no `Origin`), or any reverse-proxy/CDN forwarding header returns `403`. Non-browser loopback tools (the repo QA harnesses POST the token endpoint with no `Origin`) and the explicit `HOST=0.0.0.0` LAN opt-in keep working — the gate deliberately does not require a loopback remote address; that stricter requirement belongs only to the credential panel (`admitKeySetupRequest`). Vite's host check (`allowedHosts`) rejects a rebinding `Host` before any handler runs, in every mode, and the gate is defense in depth behind it: the LAN opt-in keeps that check and accepts only IP addresses, `localhost` and names listed in `GEV_ALLOWED_HOSTS`. **Limit:** a name you list there is trusted like the app's own address, so list only names you control.
+- **Cross-site gate on cost/log endpoints.** The cost-bearing (`/api/realtime/token`, `/api/openai/hud-summary`, `/api/google/nearby-places`) and log (`/api/realtime/debug-log`) endpoints refuse cross-site browser requests: a foreign or opaque `Origin`, a `Sec-Fetch-Site` other than `same-origin`/`none` (this is what blocks an `<img>`/navigation that carries no `Origin`), or any reverse-proxy/CDN forwarding header returns `403`. Non-browser loopback tools (the repo QA harnesses POST the token endpoint with no `Origin`) and the explicit `HOST=0.0.0.0` LAN opt-in keep working — the gate deliberately does not require a loopback remote address; that stricter requirement belongs only to the credential panel (`admitKeySetupRequest`). The Host check (`allowedHosts`, applied by `hostCheckPlugin` ahead of every route, since Vite's own check runs only after plugin middleware) rejects a rebinding `Host` before any handler runs, in every mode, and the gate is defense in depth behind it: the LAN opt-in keeps that check and accepts only IP addresses, `localhost` and names listed in `GEV_ALLOWED_HOSTS`. **Limit:** a name you list there is trusted like the app's own address, so list only names you control.
 - **Full Content-Security-Policy.** The dev and preview servers send a real CSP (`script-src 'self' 'unsafe-eval' blob:`: no inline script and no script from any other origin; `blob:` covers the object URLs Cesium's bundled workers bootstrap through in the built app), alongside the existing `X-Frame-Options: DENY` and `frame-ancestors 'none'`. `'unsafe-eval'` stays because Knockout, bundled inside Cesium's widgets package, resolves the global object with `eval` at load time and the globe does not initialize without it; styles permit `'unsafe-inline'` and Google Fonts because Vite's dev client injects `<style>` elements.
 
 ## Network exposure — the operator threat model

build/allowedHosts.js

@@ -6,6 +6,9 @@
  * connections. It must not turn into a wildcard Host-header policy: this server
  * brokers configured API keys through local proxy routes.
  */
+
+import { isIP } from 'node:net';
+
 export const DEFAULT_ALLOWED_HOSTS = Object.freeze(['localhost', '127.0.0.1']);
 
 /**
@@ -24,3 +27,68 @@ export function resolveAllowedHosts(configuredHosts) {
     .filter((host) => host && !host.startsWith('.') && !host.includes('*'));
   return [...new Set([...DEFAULT_ALLOWED_HOSTS, ...hosts])];
 }
+
+/**
+ * Whether a Host header names a host the server answers, by Vite's own rule:
+ * IP addresses, `localhost` and `*.localhost` always; then `additional` names
+ * (the configured server host) and `allowedHosts` (a leading dot allows a
+ * domain and its subdomains). `allowedHosts === true` allows every host.
+ *
+ * @param {string|undefined} hostHeader
+ * @param {string[]|true} allowedHosts
+ * @param {string[]} [additional]
+ * @returns {boolean}
+ */
+export function isAllowedHost(hostHeader, allowedHosts, additional = []) {
+  if (allowedHosts === true) return true;
+  const host = String(hostHeader ?? '').trim();
+  if (!host) return false;
+  if (host[0] === '[') {
+    const end = host.indexOf(']');
+    return end > 0 && isIP(host.slice(1, end)) === 6;
+  }
+  const colon = host.indexOf(':');
+  const hostname = (colon === -1 ? host : host.slice(0, colon)).toLowerCase();
+  if (isIP(hostname) === 4) return true;
+  if (hostname === 'localhost' || hostname.endsWith('.localhost')) return true;
+  if (additional.includes(hostname)) return true;
+  return (allowedHosts || []).some(
+    (allowed) =>
+      allowed === hostname ||
+      (allowed[0] === '.' &&
+        (allowed.slice(1) === hostname || hostname.endsWith(allowed))),
+  );
+}
+
+/**
+ * Vite plugin that applies the Host check before every other middleware.
+ * Vite installs its own check after the middleware plugins add in
+ * `configureServer`, so without this the app's `/api` routes would answer any
+ * Host, including a DNS-rebinding name. It runs first (`enforce: 'pre'`) and
+ * uses the same allowed hosts as Vite, on the dev and preview servers.
+ */
+export function hostCheckPlugin() {
+  const middleware = (config, preview) => {
+    const allowed = preview
+      ? config.preview.allowedHosts
+      : config.server.allowedHosts;
+    const additional = [config.server.host, config.preview.host].filter(
+      (value) => typeof value === 'string' && value,
+    );
+    return (req, res, next) => {
+      if (isAllowedHost(req.headers.host, allowed, additional)) return next();
+      res.writeHead(403, { 'Content-Type': 'text/plain' });
+      res.end('Blocked request. This host is not allowed.');
+    };
+  };
+  return {
+    name: 'host-check',
+    enforce: 'pre',
+    configureServer(server) {
+      server.middlewares.use(middleware(server.config, false));
+    },
+    configurePreviewServer(server) {
+      server.middlewares.use(middleware(server.config, true));
+    },
+  };
+}

build/vite.js

@@ -1,6 +1,6 @@
 import { applicationHtmlPlugin } from './application-html.js';
 import cesium from 'vite-plugin-cesium';
-import { DEFAULT_ALLOWED_HOSTS } from './allowedHosts.js';
+import { DEFAULT_ALLOWED_HOSTS, hostCheckPlugin } from './allowedHosts.js';
 import { embedFramingPlugin } from './embed-framing.js';
 import { panelBuildPlugin } from './panel.js';
 
@@ -53,6 +53,8 @@ export function createBrowserViteConfig({
 } = {}) {
   return {
     plugins: [
+      // First, so no provider route answers a Host the server does not allow.
+      hostCheckPlugin(),
       cesium(),
       applicationHtmlPlugin(),
       ...plugins,

src/tooling/allowedHosts.test.mjs

@@ -1,7 +1,11 @@
 import test from 'node:test';
 import assert from 'node:assert/strict';
+import { request as httpRequest } from 'node:http';
+import { fileURLToPath } from 'node:url';
 import {
   DEFAULT_ALLOWED_HOSTS,
+  hostCheckPlugin,
+  isAllowedHost,
   resolveAllowedHosts,
 } from '../../build/allowedHosts.js';
 
@@ -32,3 +36,118 @@ test('rejects suffix and wildcard entries so every LAN hostname is explicit', ()
     'globe.lan',
   ]);
 });
+
+test('a Host is allowed by the same rule Vite applies', () => {
+  const allowed = ['localhost', '127.0.0.1', 'globe.lan', '.corp.example'];
+  for (const host of [
+    'localhost:4173',
+    'LOCALHOST:4173',
+    'app.localhost',
+    '127.0.0.1:4173',
+    '192.168.1.20:4173',
+    '[::1]:4173',
+    'globe.lan:4173',
+    'corp.example',
+    'a.corp.example:8080',
+    'office:4173',
+  ])
+    assert.equal(isAllowedHost(host, allowed, ['office']), true, host);
+  for (const host of [
+    undefined,
+    '',
+    'evil.example:4173',
+    'globe.lan.evil.example',
+    'localhost.evil.example',
+    'mybox.local:4173',
+    '[not-an-ip]:4173',
+  ])
+    assert.equal(isAllowedHost(host, allowed, ['office']), false, String(host));
+  assert.equal(isAllowedHost('anything.example', true), true);
+});
+
+test('the Host check is installed first on the dev and preview servers', () => {
+  const plugin = hostCheckPlugin();
+  assert.equal(plugin.enforce, 'pre');
+  for (const hook of ['configureServer', 'configurePreviewServer']) {
+    let middleware;
+    plugin[hook]({
+      config: {
+        server: { allowedHosts: ['localhost'], host: 'localhost' },
+        preview: { allowedHosts: ['localhost'], host: undefined },
+      },
+      middlewares: { use: (fn) => (middleware = fn) },
+    });
+    const respond = (host) => {
+      const res = {
+        status: null,
+        writeHead(status) {
+          this.status = status;
+        },
+        end() {},
+      };
+      let passed = false;
+      middleware({ headers: { host } }, res, () => (passed = true));
+      return passed ? 'next' : res.status;
+    };
+    assert.equal(respond('localhost:4173'), 'next', hook);
+    assert.equal(respond('evil.example:4173'), 403, hook);
+  }
+});
+
+test('an unlisted Host cannot reach a route a plugin mounts', async (t) => {
+  const { createServer } = await import('vite');
+  const { createBrowserViteConfig } = await import('../../build/vite.js');
+  const provider = {
+    name: 'fixture-provider',
+    configureServer(server) {
+      server.middlewares.use('/api/fixture', (req, res) => {
+        res.end('provider answered');
+      });
+    },
+  };
+  const base = createBrowserViteConfig({ plugins: [provider] });
+  const vite = await createServer({
+    ...base,
+    root: fileURLToPath(new URL('../../', import.meta.url)),
+    configFile: false,
+    envFile: false,
+    publicDir: false,
+    logLevel: 'silent',
+    // Only this test's plugins: the Host check and the fixture provider.
+    plugins: base.plugins.filter((plugin) =>
+      ['host-check', 'fixture-provider'].includes(plugin?.name),
+    ),
+    optimizeDeps: { noDiscovery: true, include: [] },
+    server: {
+      ...base.server,
+      host: '127.0.0.1',
+      port: 0,
+      hmr: false,
+      watch: null,
+    },
+  });
+  await vite.listen();
+  t.after(() => vite.close());
+  const { port } = vite.httpServer.address();
+  const get = (host) =>
+    new Promise((resolve, reject) => {
+      const request = httpRequest(
+        {
+          host: '127.0.0.1',
+          port,
+          path: '/api/fixture',
+          headers: { Host: host },
+        },
+        (response) => {
+          response.resume();
+          resolve(response.statusCode);
+        },
+      );
+      request.on('error', reject);
+      request.end();
+    });
+  assert.equal(await get(`localhost:${port}`), 200);
+  assert.equal(await get(`127.0.0.1:${port}`), 200);
+  assert.equal(await get(`evil.example:${port}`), 403);
+  assert.equal(await get(`mybox.local:${port}`), 403);
+});

src/tooling/viteBuild.test.mjs

@@ -12,7 +12,10 @@ test('explicit build inputs preserve browser-only defines, plugin order and loop
     googleApiKey: 'browser-fixture',
     cesiumToken: 'ion-fixture',
   });
-  assert.equal(config.plugins[2], plugin);
+  // The Host check runs before every other plugin's middleware.
+  assert.equal(config.plugins[0].name, 'host-check');
+  assert.equal(config.plugins[0].enforce, 'pre');
+  assert.equal(config.plugins[3], plugin);
   assert.equal(config.server.host, 'localhost');
   assert.equal(config.server.port, 4173);
   assert.deepEqual(config.server.allowedHosts, ['localhost', '127.0.0.1']);
@@ -65,7 +68,7 @@ test('build helper does not discover environment values or construct local provi
       undefined,
     );
     assert.deepEqual(
-      config.plugins.slice(2).map((plugin) => plugin.name),
+      config.plugins.slice(3).map((plugin) => plugin.name),
       ['embed-framing', 'panel-build'],
     );
   } finally {
@@ -79,7 +82,7 @@ test('root config retains existing named exports and standalone provider order',
     assert.equal(compatibility[name], value, name);
   const config = standaloneConfig({ mode: 'test' });
   assert.deepEqual(
-    config.plugins.slice(2, -4).map((plugin) => plugin.name),
+    config.plugins.slice(3, -4).map((plugin) => plugin.name),
     providers.localProviderPlugins().map((plugin) => plugin.name),
   );
   assert.equal(config.plugins.at(-5).name, 'gev-key-setup');