From c7ff33ac2e0e7f4ab16562e652a24d64e2bd2a3a Mon Sep 17 00:00:00 2001
From: Sunil <sunilnathyogi008@gmail.com>
Date: Sat, 17 Oct 2026 14:36:24 +0530
Subject: [PATCH] fix(server): admit reverse-proxied same-origin terrain
 requests

Review follow-up on #975. The shared same-site gate refuses any forwarding header, which is right for routes that spend a key, but terrain is keyless and needed for rendering: behind the reverse proxy the README documents, every /api/terrain/heights chunk got 403 and fell back to the geoid. Terrain now uses admitSameSiteKeyless, which keeps the Sec-Fetch-Site and exact-Origin checks (comparing Origin against a single X-Forwarded-Proto scheme) but does not refuse forwarding headers. The shared admitSameSite gate is unchanged for every other route. The changelog entry moves to changelog.d/975-terrain-cross-site-gate.md.

Co-authored-by: daikaginza <daikaginza@users.noreply.github.com>
---
 SECURITY.md                                |  2 +-
 changelog.d/975-terrain-cross-site-gate.md |  8 ++
 server/providers/common/same-site.js       | 45 ++++++++++
 server/providers/terrain.js                |  9 +-
 src/proxyErrorResponses.test.mjs           |  2 +-
 src/terrainHeightsBounds.test.mjs          | 96 +++++++++++++++++++++-
 6 files changed, 156 insertions(+), 6 deletions(-)
 create mode 100644 changelog.d/975-terrain-cross-site-gate.md

diff --git a/SECURITY.md b/SECURITY.md
index e53883548..b694d8dcd 100644
--- a/SECURITY.md
+++ b/SECURITY.md
@@ -73,7 +73,7 @@ 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`, `/api/google/text-search`), quota-bearing (`/api/mapillary/*`, with a per-IP limit on tiles, and `/api/tomtom/*`, backed by its persistent daily tile budget) 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.
+- **Cross-site gate on cost/log endpoints.** The cost-bearing (`/api/realtime/token`, `/api/openai/hud-summary`, `/api/google/nearby-places`, `/api/google/text-search`), quota-bearing (`/api/mapillary/*`, with a per-IP limit on tiles, and `/api/tomtom/*`, backed by its persistent daily tile budget) 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. The keyless terrain route (`/api/terrain/heights`) uses the same cross-site checks, minus the forwarding-header refusal: it guards only the per-client quota and point cache, not a key or a bill, and the map needs it to render behind a reverse proxy.
 - **Full Content-Security-Policy.** The dev and preview servers send a real CSP (`script-src 'self' 'unsafe-eval' blob:` plus the YouTube, Facebook and X scripts the Nepal event's embedded media loads and the Maps JavaScript API that Street View runs on, with a matching `frame-src` for their players and posts: no inline script and no other script 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.
 
 Allowing `maps.googleapis.com` in `script-src` also trusts its JSONP endpoints, which can bypass the script allowlist if an HTML-injection bug exists; this is an accepted limitation of loading the Maps JavaScript API, alongside the existing `'unsafe-eval'` allowance.
diff --git a/changelog.d/975-terrain-cross-site-gate.md b/changelog.d/975-terrain-cross-site-gate.md
new file mode 100644
index 000000000..6c0e42156
--- /dev/null
+++ b/changelog.d/975-terrain-cross-site-gate.md
@@ -0,0 +1,8 @@
+- Cross-site pages can no longer fill the terrain-height cache or spend the
+  visitor's own `/api/terrain/heights` rate-limit quota through the visitor's
+  browser. The route refuses a cross-site `Sec-Fetch-Site` or a foreign or
+  opaque `Origin` before rate limiting, cache access or upstream work. Unlike
+  the cost-bearing routes it still answers same-origin requests that arrive
+  through a reverse proxy, so terrain keeps rendering behind nginx, Caddy or
+  Cloudflare instead of falling back to the geoid (Sunil56224972, daikaginza,
+  #975).
diff --git a/server/providers/common/same-site.js b/server/providers/common/same-site.js
index 11e9d37b4..c5aeb610f 100644
--- a/server/providers/common/same-site.js
+++ b/server/providers/common/same-site.js
@@ -41,3 +41,48 @@ export function sameSiteGated(handler) {
     return handler(req, res, next);
   };
 }
+
+/**
+ * Proxy header values arrive client-controlled; read one only when it is a
+ * single scheme token, never a comma-separated chain.
+ * @param {import('node:http').IncomingMessage} req
+ * @returns {'http:'|'https:'}
+ */
+function forwardedProtocol(req) {
+  if (req.socket?.encrypted) return 'https:';
+  const proto = String(req.headers?.['x-forwarded-proto'] || '')
+    .trim()
+    .toLowerCase();
+  return proto === 'https' ? 'https:' : 'http:';
+}
+
+/**
+ * Cross-site gate for keyless routes the map needs in order to render
+ * (`/api/terrain/heights`). It refuses the same cross-site browser shapes as
+ * `admitSameSite` (a `Sec-Fetch-Site` other than same-origin/none, a foreign
+ * or opaque `Origin`) but does not refuse reverse-proxy forwarding headers:
+ * those protect credentials and spend, which a keyless route has neither of,
+ * and refusing them would break rendering for an instance served behind the
+ * reverse proxy the README documents. A single `X-Forwarded-Proto` supplies
+ * the scheme an `Origin` is compared against. That header cannot be attached
+ * to a cross-site browser request without a CORS preflight this server never
+ * answers, and `Sec-Fetch-Site` is still enforced regardless.
+ * @param {import('node:http').IncomingMessage} req
+ * @param {import('node:http').ServerResponse} res
+ * @returns {boolean} True when a 403 was sent.
+ */
+export function admitSameSiteKeyless(req, res) {
+  const verdict = admitSameSiteRequest({
+    hostHeader: req.headers?.host,
+    protocol: forwardedProtocol(req),
+    origin: req.headers?.origin,
+    secFetchSite: req.headers?.['sec-fetch-site'],
+    proxyHeaders: {},
+  });
+  if (verdict.ok) return false;
+  res.statusCode = verdict.status;
+  res.setHeader('Content-Type', 'application/json');
+  res.setHeader('Cache-Control', 'no-store');
+  res.end(JSON.stringify({ error: verdict.error }));
+  return true;
+}
diff --git a/server/providers/terrain.js b/server/providers/terrain.js
index b2615094e..32083d23a 100644
--- a/server/providers/terrain.js
+++ b/server/providers/terrain.js
@@ -9,7 +9,7 @@ import {
   validTerrainResult,
 } from '../../src/data/terrainHeightsProxy.js';
 import { makeRateLimiter, clientKey } from './common/rate-limit.js';
-import { admitSameSite } from './common/same-site.js';
+import { admitSameSiteKeyless } from './common/same-site.js';
 
 /**
  * Re:Earth terrain point-height proxy: batched lon/lat → ellipsoidal height
@@ -29,6 +29,8 @@ import { admitSameSite } from './common/same-site.js';
  * the route carries an always-on per-client limiter. The route also refuses
  * cross-site browser requests, so another web page cannot use the visitor's
  * browser to fill the cache or spend the visitor's own rate-limit quota.
+ * Reverse-proxied same-origin requests are admitted: terrain is keyless and
+ * needed for rendering, and a 403 would send every chunk to the geoid fallback.
  */
 export function terrainHeightsProxy(options = {}) {
   // Destructured in the body, not the signature: `proxyErrorResponses.test.mjs`
@@ -236,8 +238,9 @@ export function terrainHeightsProxy(options = {}) {
     server.middlewares.use('/api/terrain/heights', async (req, res) => {
       // Refuse cross-site browser requests (an <img> or fetch from another
       // site) before the limiter, cache or upstream see them. Same-origin app
-      // requests and non-browser loopback callers (MCP panel_request) pass.
-      if (admitSameSite(req, res)) return;
+      // requests, non-browser loopback callers (MCP panel_request) and the app
+      // served behind a reverse proxy pass.
+      if (admitSameSiteKeyless(req, res)) return;
       const send = (status, bodyObj) => {
         if (res.headersSent) return;
         res.writeHead(status, { 'Content-Type': 'application/json' });
diff --git a/src/proxyErrorResponses.test.mjs b/src/proxyErrorResponses.test.mjs
index c972fd0d2..78f3f59f0 100644
--- a/src/proxyErrorResponses.test.mjs
+++ b/src/proxyErrorResponses.test.mjs
@@ -29,7 +29,7 @@ function fixture(name, overrides = {}, preview = false) {
     makeRateLimiter, clientKey,
     // terrain.js gates cross-site requests first; fixture requests carry no
     // browser headers, so admit them like a loopback tool.
-    admitSameSite: () => false,
+    admitSameSiteKeyless: () => false,
     path, process: { cwd: () => '/fixture', env: {} },
     fsp: {
       readFile: async () => { throw new Error('cache absent'); },
diff --git a/src/terrainHeightsBounds.test.mjs b/src/terrainHeightsBounds.test.mjs
index 83edc262d..cd1a9ad36 100644
--- a/src/terrainHeightsBounds.test.mjs
+++ b/src/terrainHeightsBounds.test.mjs
@@ -16,6 +16,7 @@ import { tmpdir } from 'node:os';
 import path from 'node:path';
 import { parseTerrainPoints } from './data/terrainHeightsProxy.js';
 import { terrainHeightsProxy } from '../server/providers/terrain.js';
+import { admitSameSite } from '../server/providers/common/same-site.js';
 
 function install(plugin) {
   const routes = new Map();
@@ -224,7 +225,8 @@ test('a cross-site page cannot fill the cache or spend the visitor quota', async
     { host, 'sec-fetch-site': 'same-site' },
     { host, origin: 'https://evil.example' }, // fetch from another page
     { host, origin: 'null' }, // sandboxed frame
-    { host, 'x-forwarded-for': '203.0.113.9' }, // through a proxy
+    // Behind a reverse proxy the browser's own Sec-Fetch-Site still decides.
+    { host, 'x-forwarded-for': '203.0.113.9', 'sec-fetch-site': 'cross-site' },
   ];
   // More refused requests than the 90/min quota, each a distinct new key.
   for (let i = 0; i < 100; i += 1) {
@@ -249,6 +251,98 @@ test('a cross-site page cannot fill the cache or spend the visitor quota', async
   assert.equal(asked.length, 2);
 });
 
+test('the app served behind a reverse proxy still gets terrain', async (t) => {
+  const asked = stubTerrainUpstream(t);
+  const route = install(terrainHeightsProxy()).get('/api/terrain/heights');
+  const host = 'globe.example.lan';
+  // What nginx/Caddy/Cloudflare add in front of a same-origin app fetch. The
+  // cost-bearing routes refuse these; terrain is keyless and needed to render,
+  // so a 403 here would drop every chunk to the geoid fallback.
+  const proxied = [
+    {
+      host,
+      'sec-fetch-site': 'same-origin',
+      'x-forwarded-for': '203.0.113.9',
+    },
+    {
+      host,
+      'sec-fetch-site': 'same-origin',
+      'cf-connecting-ip': '203.0.113.9',
+    },
+    {
+      host,
+      'sec-fetch-site': 'same-origin',
+      forwarded: 'for=203.0.113.9;proto=https',
+      via: '1.1 caddy',
+    },
+    // TLS terminated at the proxy: the page origin is https, the hop is http.
+    {
+      host,
+      origin: `https://${host}`,
+      'sec-fetch-site': 'same-origin',
+      'x-forwarded-proto': 'https',
+      'x-forwarded-for': '203.0.113.9',
+    },
+  ];
+  for (const [i, reqHeaders] of proxied.entries()) {
+    const answer = await request(route, {
+      url: `/?points=${(-97.8 - i / 1000).toFixed(5)},30.26`,
+      reqHeaders,
+    });
+    assert.equal(answer.statusCode, 200, JSON.stringify(reqHeaders));
+  }
+  assert.equal(asked.length, proxied.length);
+
+  // Proxied or not, a cross-site page is still refused before any work.
+  for (const reqHeaders of [
+    { host, 'x-forwarded-for': '203.0.113.9', 'sec-fetch-site': 'cross-site' },
+    {
+      host,
+      'x-forwarded-proto': 'https',
+      origin: 'https://evil.example',
+    },
+    // A forwarded scheme does not make an http Origin match an https page.
+    { host, 'x-forwarded-proto': 'https', origin: `http://${host}` },
+  ]) {
+    const answer = await request(route, {
+      url: '/?points=-97.9,30.26',
+      reqHeaders,
+    });
+    assert.equal(answer.statusCode, 403, JSON.stringify(reqHeaders));
+  }
+  assert.equal(asked.length, proxied.length, 'refusals cost no upstream call');
+});
+
+test('cost-bearing routes still refuse proxied requests', () => {
+  // The keyless exemption is scoped to terrain; the shared gate is unchanged.
+  const res = {
+    statusCode: 200,
+    headers: {},
+    setHeader(name, value) {
+      this.headers[name.toLowerCase()] = value;
+    },
+    end(body) {
+      this.body = body;
+    },
+  };
+  const refused = admitSameSite(
+    {
+      headers: {
+        host: 'globe.example.lan',
+        'sec-fetch-site': 'same-origin',
+        'x-forwarded-for': '203.0.113.9',
+      },
+      socket: {},
+    },
+    res,
+  );
+  assert.equal(refused, true);
+  assert.equal(res.statusCode, 403);
+  assert.deepEqual(JSON.parse(res.body), {
+    error: 'Proxied requests are not accepted',
+  });
+});
+
 test('a second client keeps its own quota', async (t) => {
   stubFetch(t, async () =>
     Response.json([{ lng: -97.74, lat: 30.26, height: 150 }]),