diff --git a/changelog.d/1427-military-installations-cross-site-gate.md b/changelog.d/1427-military-installations-cross-site-gate.md
new file mode 100644
index 000000000..35d9e73e7
--- /dev/null
+++ b/changelog.d/1427-military-installations-cross-site-gate.md
@@ -0,0 +1,4 @@
+- The military-installations proxy (`/api/military-installations`) now refuses
+  cross-site and reverse-proxy-forwarded browser requests with 403 before any
+  Overpass work, through the same shared gate as `/api/overpass`. Same-origin
+  app requests and local tools such as curl still work (@Sunil56224972, #1427).
diff --git a/docs/CURRENT-STATE.md b/docs/CURRENT-STATE.md
index 8a8a5aa1d..9e3c8709a 100644
--- a/docs/CURRENT-STATE.md
+++ b/docs/CURRENT-STATE.md
@@ -5086,6 +5086,8 @@ repointing `OVERPASS_UPSTREAMS` refetches instead of serving another instance's
 answers; untagged entries stop serving once an instance is configured.
 
 The shared transport guards `/api/overpass` and `/api/military-installations`.
+Both query handlers refuse cross-site and forwarded browser requests through
+the shared local-request gate, before any rate-limit, cache or upstream work.
 With no configured upstream, each route serves existing cache data (including
 expired entries, marked stale with the original cache/retrieval date) without
 refresh. An annotation miss returns HTTP 503, `OVERPASS_NOT_CONFIGURED`,
diff --git a/scripts/package-boundaries.json b/scripts/package-boundaries.json
index 303107647..217628822 100644
--- a/scripts/package-boundaries.json
+++ b/scripts/package-boundaries.json
@@ -432,7 +432,9 @@
       "server/providers/overpass/transport.js",
       "src/sources/httpBody.js",
       "src/i18n/marker.js",
-      "src/sources/rateLimit.js"
+      "src/sources/rateLimit.js",
+      "server/providers/common/same-site.js",
+      "src/localRequestGate.mjs"
     ],
     "external": []
   },
diff --git a/server/providers/military-installations.js b/server/providers/military-installations.js
index 7d252b8ed..1b6c82107 100644
--- a/server/providers/military-installations.js
+++ b/server/providers/military-installations.js
@@ -1,4 +1,5 @@
 import { makeRateLimiter, clientKey } from './common/rate-limit.js';
+import { admitSameSite } from './common/same-site.js';
 import {
   MILITARY_INSTALLATION_ELEMENT_CAP,
   MILITARY_INSTALLATION_MAX_RESPONSE_BYTES,
@@ -97,6 +98,7 @@ function militaryInstallationsProxy() {
         res.end(JSON.stringify({ error: 'Method Not Allowed' }));
         return;
       }
+      if (admitSameSite(req, res)) return;
       const url = new URL(req.url, 'http://localhost');
       const requested = validMilitaryInstallationBox(url.searchParams);
       if (!requested) {
diff --git a/src/overpassOffload.test.mjs b/src/overpassOffload.test.mjs
index 602bab8e4..7ef6b0c2b 100644
--- a/src/overpassOffload.test.mjs
+++ b/src/overpassOffload.test.mjs
@@ -54,14 +54,22 @@ async function call(handlers, url, init = {}) {
   Object.assign(req, {
     method: init.method || 'GET',
     url: parsed.pathname.slice(mount.length) + parsed.search || '/',
-    headers: {},
+    headers: init.headers || {},
     socket: { remoteAddress: '127.0.0.1' },
   });
-  let status, headers, body;
+  let status, body;
+  let headers = {};
   await handlers.get(mount)(req, {
+    // The cross-site gate answers through statusCode/setHeader, not writeHead.
+    set statusCode(s) {
+      status = s;
+    },
+    setHeader(name, value) {
+      headers[name] = value;
+    },
     writeHead(s, h) {
       status = s;
-      headers = h;
+      headers = { ...headers, ...h };
     },
     end(b) {
       body = b;
@@ -166,6 +174,36 @@ test('zero egress: every Overpass consumer reaches real default handlers, and re
   );
 });
 
+test('the installations proxy refuses cross-site and forwarded requests before any Overpass work', async (t) => {
+  env(t);
+  t.mock.method(globalThis, 'fetch', () =>
+    assert.fail('unexpected upstream fetch'),
+  );
+  const handlers = routes(militaryInstallationsProxy());
+  const url =
+    '/api/military-installations?south=48.8&west=2.2&north=48.9&east=2.4';
+  for (const headers of [
+    { 'sec-fetch-site': 'cross-site' },
+    { 'sec-fetch-site': 'same-site' },
+    { origin: 'https://foreign.example' },
+    { origin: 'null' },
+    { 'sec-fetch-site': 'same-origin', 'x-forwarded-for': '203.0.113.9' },
+  ]) {
+    const response = await call(handlers, url, { headers });
+    assert.equal(response.status, 403, JSON.stringify(headers));
+    assert.equal(response.headers.get('cache-control'), 'no-store');
+  }
+  for (const headers of [
+    {},
+    { origin: 'http://localhost:4173', 'sec-fetch-site': 'same-origin' },
+  ]) {
+    const response = await call(handlers, url, {
+      headers: { host: 'localhost:4173', ...headers },
+    });
+    assert.notEqual(response.status, 403, JSON.stringify(headers));
+  }
+});
+
 test('an unconfigured server is probed once and never sent a feature query', async (t) => {
   env(t);
   t.mock.method(globalThis, 'fetch', () =>