diff --git a/cloud/public/index.php b/cloud/public/index.php
index 7b16dc1..bf653ac 100644
--- a/cloud/public/index.php
+++ b/cloud/public/index.php
@@ -30,8 +30,8 @@ $thr = new PdoThresholdRepository($pdo);
 $audit = new PdoAuditRepository($pdo);
 
 $ingest = new IngestController($cfg, $devices, $nonces, $rate, $events, $snaps);
-$config = new ConfigController($devices, $zones, $thr);
-$heartbeat = new HeartbeatController($cfg, $devices);
+$config = new ConfigController($devices, $zones, $thr, $nonces, $cfg);
+$heartbeat = new HeartbeatController($cfg, $devices, $nonces);
 $auth = new AuthController($users, $audit, $rate);
 $csrfCtl = new CsrfController();
 $list = new EventListController($events, $sess);
@@ -47,7 +47,7 @@ $render = function (string $view): Response {
 $r = new Router();
 $r->add('POST', '/api/events', fn(Request $q) => $ingest->handle($q, $now, (string)($_SERVER['REMOTE_ADDR'] ?? '')));
 $r->add('POST', '/api/heartbeat', fn(Request $q) => $heartbeat->post($q, $now));
-$r->add('GET', '/api/config', fn(Request $q) => $config->get($q));
+$r->add('GET', '/api/config', fn(Request $q) => $config->get($q, $now));
 $r->add('GET', '/api/csrf', fn(Request $q) => $csrfCtl->token($q, $sess));
 $r->add('POST', '/login', fn(Request $q) => $auth->login($q, $sess, $now, (string)($_SERVER['REMOTE_ADDR'] ?? '')));
 $r->add('POST', '/logout', fn(Request $q) => $auth->logout($sess));
diff --git a/cloud/src/Api/ConfigController.php b/cloud/src/Api/ConfigController.php
index edf3f0f..785a628 100644
--- a/cloud/src/Api/ConfigController.php
+++ b/cloud/src/Api/ConfigController.php
@@ -2,17 +2,19 @@
 declare(strict_types=1);
 namespace App\Api;
 
+use App\Config;
 use App\Http\{Request, Response};
 use App\Security\Hmac;
-use App\Repository\{DeviceRepository, ZoneRepository, ThresholdRepository};
+use App\Repository\{DeviceRepository, ZoneRepository, ThresholdRepository, NonceRepository};
 
 final class ConfigController
 {
     public function __construct(
-        private DeviceRepository $devices, private ZoneRepository $zones, private ThresholdRepository $thresholds
+        private DeviceRepository $devices, private ZoneRepository $zones, private ThresholdRepository $thresholds,
+        private NonceRepository $nonces, private Config $cfg,
     ) {}
 
-    public function get(Request $req): Response
+    public function get(Request $req, int $now): Response
     {
         $deviceId = (string)$req->query('device_id');
         $secret = $deviceId !== '' ? $this->devices->secretFor($deviceId) : null;
@@ -20,6 +22,14 @@ final class ConfigController
         if ($secret === null || !Hmac::verify($secret, $nonce, $ts, $req->body(), $sig)) {
             return Response::json(['error' => 'unauthorized'], 401);
         }
+        if (abs($now - (int)(float)$ts) > $this->cfg->timestampWindow()) {
+            return Response::json(['error' => 'stale'], 401);
+        }
+        if ($nonce === '' || $this->nonces->seen($nonce)) {
+            return Response::json(['error' => 'replay'], 401);
+        }
+        $this->nonces->remember($nonce, $now + $this->cfg->nonceTtl());
+
         return Response::json([
             'version' => $this->devices->configVersion($deviceId),
             'zones' => $this->zones->forDevice($deviceId),
diff --git a/cloud/src/Api/HeartbeatController.php b/cloud/src/Api/HeartbeatController.php
index 1f9cd32..7a4c404 100644
--- a/cloud/src/Api/HeartbeatController.php
+++ b/cloud/src/Api/HeartbeatController.php
@@ -5,11 +5,11 @@ namespace App\Api;
 use App\Config;
 use App\Http\{Request, Response};
 use App\Security\Hmac;
-use App\Repository\DeviceRepository;
+use App\Repository\{DeviceRepository, NonceRepository};
 
 final class HeartbeatController
 {
-    public function __construct(private Config $cfg, private DeviceRepository $devices) {}
+    public function __construct(private Config $cfg, private DeviceRepository $devices, private NonceRepository $nonces) {}
 
     public function post(Request $req, int $now): Response
     {
@@ -20,6 +20,14 @@ final class HeartbeatController
         if ($secret === null || !Hmac::verify($secret, $nonce, $ts, $req->body(), $sig)) {
             return Response::json(['error' => 'unauthorized'], 401);
         }
+        if (abs($now - (int)(float)$ts) > $this->cfg->timestampWindow()) {
+            return Response::json(['error' => 'stale'], 401);
+        }
+        if ($nonce === '' || $this->nonces->seen($nonce)) {
+            return Response::json(['error' => 'replay'], 401);
+        }
+        $this->nonces->remember($nonce, $now + $this->cfg->nonceTtl());
+
         $this->devices->touchHeartbeat($deviceId, [
             'fps' => (float)($b['fps'] ?? 0), 'temp' => (float)($b['temp'] ?? 0),
             'throttle' => (bool)($b['throttle'] ?? false), 'config_version' => (int)($b['config_version'] ?? 0),
diff --git a/cloud/tests/ApiSyncTest.php b/cloud/tests/ApiSyncTest.php
index 776a684..761f411 100644
--- a/cloud/tests/ApiSyncTest.php
+++ b/cloud/tests/ApiSyncTest.php
@@ -5,14 +5,13 @@ use App\Config;
 use App\Http\Request;
 use App\Security\Hmac;
 use App\Api\{ConfigController, HeartbeatController};
-use App\Tests\Support\{InMemoryDeviceRepository, InMemoryZoneRepository, InMemoryThresholdRepository};
+use App\Tests\Support\{InMemoryDeviceRepository, InMemoryZoneRepository, InMemoryThresholdRepository, InMemoryNonceRepository};
 use PHPUnit\Framework\TestCase;
 
 final class ApiSyncTest extends TestCase
 {
-    private function signed(string $method, string $path, string $secret, array $q = [], array $body = []): Request {
+    private function signed(string $method, string $path, string $secret, array $q = [], array $body = [], string $nonce = 'n1', string $ts = '1000'): Request {
         $raw = $body ? json_encode($body) : '';
-        $nonce = 'n1'; $ts = '1000';
         $sig = Hmac::sign($secret, $nonce, $ts, $raw);
         return new Request($method, $path, ['X-Nonce' => $nonce, 'X-Timestamp' => $ts, 'X-Signature' => $sig], $raw, $q, []);
     }
@@ -20,8 +19,10 @@ final class ApiSyncTest extends TestCase
         $dev = new InMemoryDeviceRepository(['pi-1' => 'sek'], ['pi-1' => 7]);
         $zones = new InMemoryZoneRepository(); $zones->save(['device_id' => 'pi-1', 'camera_id' => 'cam-1', 'level' => 'restricted', 'polygon_json' => '[[0,0],[9,0],[9,9]]']);
         $thr = new InMemoryThresholdRepository(['pi-1' => ['fall_prone_s' => 3.0]]);
-        $c = new ConfigController($dev, $zones, $thr);
-        $res = $c->get($this->signed('GET', '/api/config', 'sek', ['device_id' => 'pi-1']));
+        $nonces = new InMemoryNonceRepository();
+        $cfg = Config::fromArray(['timestamp_window' => 300]);
+        $c = new ConfigController($dev, $zones, $thr, $nonces, $cfg);
+        $res = $c->get($this->signed('GET', '/api/config', 'sek', ['device_id' => 'pi-1']), now: 1000);
         $this->assertSame(200, $res->status());
         $data = json_decode($res->body(), true);
         $this->assertSame(7, $data['version']);
@@ -30,17 +31,58 @@ final class ApiSyncTest extends TestCase
     }
     public function testConfigRejectsBadSignature(): void {
         $dev = new InMemoryDeviceRepository(['pi-1' => 'sek']);
-        $c = new ConfigController($dev, new InMemoryZoneRepository(), new InMemoryThresholdRepository());
-        $res = $c->get($this->signed('GET', '/api/config', 'WRONG', ['device_id' => 'pi-1']));
+        $c = new ConfigController($dev, new InMemoryZoneRepository(), new InMemoryThresholdRepository(), new InMemoryNonceRepository(), Config::fromArray([]));
+        $res = $c->get($this->signed('GET', '/api/config', 'WRONG', ['device_id' => 'pi-1']), now: 1000);
         $this->assertSame(401, $res->status());
     }
+    public function testConfigRejectsReplayedNonce(): void {
+        $dev = new InMemoryDeviceRepository(['pi-1' => 'sek'], ['pi-1' => 7]);
+        $zones = new InMemoryZoneRepository();
+        $thr = new InMemoryThresholdRepository();
+        $nonces = new InMemoryNonceRepository();
+        $cfg = Config::fromArray(['timestamp_window' => 300]);
+        $c = new ConfigController($dev, $zones, $thr, $nonces, $cfg);
+        $req = $this->signed('GET', '/api/config', 'sek', ['device_id' => 'pi-1'], [], 'replay-nonce', '1000');
+        $this->assertSame(200, $c->get($req, now: 1000)->status());
+        $this->assertSame(401, $c->get($req, now: 1000)->status()); // same nonce replayed
+    }
+    public function testConfigRejectsStaleTimestamp(): void {
+        $dev = new InMemoryDeviceRepository(['pi-1' => 'sek']);
+        $zones = new InMemoryZoneRepository();
+        $thr = new InMemoryThresholdRepository();
+        $nonces = new InMemoryNonceRepository();
+        $cfg = Config::fromArray(['timestamp_window' => 300]);
+        $c = new ConfigController($dev, $zones, $thr, $nonces, $cfg);
+        $req = $this->signed('GET', '/api/config', 'sek', ['device_id' => 'pi-1'], [], 'stale-nonce', '1000');
+        $this->assertSame(401, $c->get($req, now: 5000)->status()); // 4000s > 300 window
+    }
     public function testHeartbeatStored(): void {
         $cfg = Config::fromArray([]);
         $dev = new InMemoryDeviceRepository(['pi-1' => 'sek']);
-        $c = new HeartbeatController($cfg, $dev);
+        $nonces = new InMemoryNonceRepository();
+        $c = new HeartbeatController($cfg, $dev, $nonces);
         $body = ['device_id' => 'pi-1', 'fps' => 12.0, 'temp' => 55.0, 'throttle' => false, 'config_version' => 7];
         $res = $c->post($this->signed('POST', '/api/heartbeat', 'sek', [], $body), now: 1000);
         $this->assertSame(200, $res->status());
         $this->assertSame(12.0, $dev->heartbeats['pi-1']['fps']);
     }
+    public function testHeartbeatRejectsReplayedNonce(): void {
+        $cfg = Config::fromArray([]);
+        $dev = new InMemoryDeviceRepository(['pi-1' => 'sek']);
+        $nonces = new InMemoryNonceRepository();
+        $c = new HeartbeatController($cfg, $dev, $nonces);
+        $body = ['device_id' => 'pi-1', 'fps' => 12.0, 'temp' => 55.0, 'throttle' => false, 'config_version' => 7];
+        $req = $this->signed('POST', '/api/heartbeat', 'sek', [], $body, 'hb-replay', '1000');
+        $this->assertSame(200, $c->post($req, now: 1000)->status());
+        $this->assertSame(401, $c->post($req, now: 1000)->status()); // same nonce replayed
+    }
+    public function testHeartbeatRejectsStaleTimestamp(): void {
+        $cfg = Config::fromArray([]);
+        $dev = new InMemoryDeviceRepository(['pi-1' => 'sek']);
+        $nonces = new InMemoryNonceRepository();
+        $c = new HeartbeatController($cfg, $dev, $nonces);
+        $body = ['device_id' => 'pi-1', 'fps' => 12.0, 'temp' => 55.0, 'throttle' => false, 'config_version' => 7];
+        $req = $this->signed('POST', '/api/heartbeat', 'sek', [], $body, 'hb-stale', '1000');
+        $this->assertSame(401, $c->post($req, now: 5000)->status()); // 4000s > 300 default window
+    }
 }