diff --git a/.env.example b/.env.example
index a74c664..865ac96 100644
--- a/.env.example
+++ b/.env.example
@@ -174,6 +174,12 @@ CACHE_DURATION=3600
 # Content-Security-Policy：off | report-only（預設）| enforce
 # CSP_MODE=report-only
 #
+# HSTS（僅 APP_ENV=production 送出；不含 preload）
+# 有效期（秒），預設一年；設為 0 停用
+# HSTS_MAX_AGE=31536000
+# 確認同網域的所有子網域都只走 HTTPS 後才設為 true
+# HSTS_INCLUDE_SUBDOMAINS=false
+#
 # 反向代理 CIDR（逗號分隔，擴充 request.trustedHosts）
 # TRUSTED_PROXY_CIDRS=10.0.0.0/8,172.16.0.0/12
 #
diff --git a/CHANGELOG.md b/CHANGELOG.md
index 4a0ff20..354ee4a 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -29,6 +29,7 @@
 
 ### Security
 
+* HSTS 改由安全標頭元件於正式環境的每個回應送出，預設 `max-age=31536000`，不再帶難以撤回的 `preload`；`includeSubDomains` 需確認所有子網域皆為 HTTPS 後以 `HSTS_INCLUDE_SUBDOMAINS=true` 開啟。原本僅在部分存檔動作才送出
 * 測試專用登入路由移出正式程式目錄（`tests/_support/TestLoginController.php`），只由測試設定掛載，且須 Yii 測試模式加上 `APP_ENV=testing`／`test` 才可使用，其他情況回 404
 * **升級注意**：正式環境（`APP_ENV=production`）必須為 `YII_ENV=prod`（或未設定）且 `YII_DEBUG=false`，否則系統拒絕啟動並列出原因；升級前請先檢查正式機 `.env`
 * 投票頁自訂欄位標題、候選名單內容與紙本選票的中英文資料統一淨化原本直接輸出的 HTML；列印分段表頭也套用淨化，保留既有換行與合法排版
diff --git a/components/SecurityHeadersBootstrap.php b/components/SecurityHeadersBootstrap.php
index bc38faa..c8f1c25 100644
--- a/components/SecurityHeadersBootstrap.php
+++ b/components/SecurityHeadersBootstrap.php
@@ -24,11 +24,15 @@ public function bootstrap($app): void
         Event::on(Response::class, Response::EVENT_BEFORE_SEND, static function ($event): void {
             /** @var Response $response */
             $response = $event->sender;
+            $headers = $response->headers;
+
+            // HSTS 適用所有回應（含檔案下載）
+            static::applyStrictTransportSecurity($headers);
+
             if ($response->format === Response::FORMAT_RAW) {
                 return;
             }
 
-            $headers = $response->headers;
             $headers->set('X-Content-Type-Options', 'nosniff');
             $headers->set('X-Frame-Options', 'SAMEORIGIN');
             $headers->set('Referrer-Policy', 'strict-origin-when-cross-origin');
@@ -39,6 +43,33 @@ public function bootstrap($app): void
         });
     }
 
+    /**
+     * 正式環境送出 HSTS。
+     *
+     * 瀏覽器會忽略經 HTTP 收到的 HSTS，因此不需判斷是否為 HTTPS 連線（反向代理終結 TLS 時亦適用）。
+     * 不加 preload（難以撤回）；includeSubDomains 需確認同網域所有子網域皆為 HTTPS 後再以
+     * HSTS_INCLUDE_SUBDOMAINS=true 開啟。HSTS_MAX_AGE=0 可停用。
+     */
+    private static function applyStrictTransportSecurity($headers): void
+    {
+        if (!\app\config\ConfigValidator::isProductionEnvironment()) {
+            return;
+        }
+
+        $maxAge = getenv('HSTS_MAX_AGE');
+        $maxAge = ($maxAge === false || trim($maxAge) === '') ? 31536000 : (int) $maxAge;
+        if ($maxAge <= 0) {
+            return;
+        }
+
+        $value = 'max-age=' . $maxAge;
+        if (filter_var(getenv('HSTS_INCLUDE_SUBDOMAINS') ?: 'false', FILTER_VALIDATE_BOOLEAN)) {
+            $value .= '; includeSubDomains';
+        }
+
+        $headers->set('Strict-Transport-Security', $value);
+    }
+
     private static function applyContentSecurityPolicy($headers): void
     {
         $mode = strtolower(trim(getenv('CSP_MODE') ?: 'report-only'));
diff --git a/components/helper/ArrayHelper.php b/components/helper/ArrayHelper.php
index 2ffcd80..e13868f 100644
--- a/components/helper/ArrayHelper.php
+++ b/components/helper/ArrayHelper.php
@@ -59,9 +59,7 @@ public static function getAttributesMigration($attributes, $oldAttributes)
     {
         // 先確認是否有差異
         $diff = array_diff_assoc($attributes, $oldAttributes);
-        header('Content-Type: text/html; charset=utf-8');
-        // Missing HSTS Header
-        header('Strict-Transport-Security: max-age=31536000; includeSubDomains; preload');
+        // 安全標頭（含 HSTS）統一由 SecurityHeadersBootstrap 送出
         if (empty($diff)) {
             return [];
         }
diff --git a/tests/unit/components/SecurityHeadersBootstrapTest.php b/tests/unit/components/SecurityHeadersBootstrapTest.php
index 7d1a510..62b3b41 100644
--- a/tests/unit/components/SecurityHeadersBootstrapTest.php
+++ b/tests/unit/components/SecurityHeadersBootstrapTest.php
@@ -51,6 +51,65 @@ public function testCspOffSkipsHeader()
         putenv('CSP_MODE');
     }
 
+    /**
+     * 以全新 Response 觸發，避免沿用其他測試留下的標頭
+     */
+    private function hstsFor(array $env, string $format = Response::FORMAT_HTML): ?string
+    {
+        $names = ['APP_ENV', 'HSTS_MAX_AGE', 'HSTS_INCLUDE_SUBDOMAINS'];
+        $saved = [];
+        foreach ($names as $name) {
+            $saved[$name] = getenv($name);
+            putenv(array_key_exists($name, $env) ? "{$name}={$env[$name]}" : $name);
+        }
+        try {
+            (new SecurityHeadersBootstrap())->bootstrap(\Yii::$app);
+            $response = new Response(['format' => $format]);
+            $response->trigger(Response::EVENT_BEFORE_SEND);
+            return $response->headers->get('Strict-Transport-Security');
+        } finally {
+            foreach ($saved as $name => $value) {
+                putenv($value === false ? $name : "{$name}={$value}");
+            }
+        }
+    }
+
+    public function testProductionSendsHstsWithoutPreloadOrSubdomainsByDefault()
+    {
+        $this->assertSame('max-age=31536000', $this->hstsFor(['APP_ENV' => 'production']));
+    }
+
+    public function testHstsIncludeSubdomainsIsOptIn()
+    {
+        $value = $this->hstsFor(['APP_ENV' => 'production', 'HSTS_INCLUDE_SUBDOMAINS' => 'true']);
+        $this->assertSame('max-age=31536000; includeSubDomains', $value);
+        $this->assertStringNotContainsString('preload', $value);
+    }
+
+    public function testHstsMaxAgeConfigurableAndZeroDisables()
+    {
+        $this->assertSame('max-age=600', $this->hstsFor(['APP_ENV' => 'production', 'HSTS_MAX_AGE' => '600']));
+        $this->assertNull($this->hstsFor(['APP_ENV' => 'production', 'HSTS_MAX_AGE' => '0']));
+    }
+
+    public function testNonProductionSendsNoHsts()
+    {
+        foreach (['development', 'testing'] as $appEnv) {
+            $this->assertNull($this->hstsFor(['APP_ENV' => $appEnv]), $appEnv);
+        }
+    }
+
+    public function testHstsAppliesToRawResponses()
+    {
+        $this->assertSame('max-age=31536000', $this->hstsFor(['APP_ENV' => 'production'], Response::FORMAT_RAW));
+    }
+
+    public function testAttributeDiffHelperNoLongerSendsHeaders()
+    {
+        $source = file_get_contents(dirname(__DIR__, 3) . '/components/helper/ArrayHelper.php');
+        $this->assertStringNotContainsString('Strict-Transport-Security', $source);
+    }
+
     public function testRawFormatSkipsSecurityHeaders()
     {
         (new SecurityHeadersBootstrap())->bootstrap(\Yii::$app);