diff --git a/app/Http/Controllers/Admin/PlanController.php b/app/Http/Controllers/Admin/PlanController.php
index 4915ee0..232591a 100644
--- a/app/Http/Controllers/Admin/PlanController.php
+++ b/app/Http/Controllers/Admin/PlanController.php
@@ -149,7 +149,12 @@ class PlanController extends Controller
 
         $back = (string) $request->query('back', '');
         // back 需为站内相对路径，并拒绝引号/尖括号，避免后续页面以 `{!! !!}` 原样输出时引入 XSS 风险。
-        $safeBack = (str_starts_with($back, '/') && !preg_match('/["\'<>]/', $back)) ? $back : '';
+        $safeBack = (str_starts_with($back, '/')
+            && !preg_match('/["\'<>]/', $back)
+            // back 本身不应再包含 back（避免无限嵌套导致 URL 膨胀）
+            && !preg_match('/(?:^|[?&])back=/', $back))
+            ? $back
+            : '';
 
         return view('admin.plans.form', [
             'plan' => new Plan(),
@@ -169,7 +174,12 @@ class PlanController extends Controller
 
         $back = (string) $request->input('back', '');
         // back 需为站内相对路径，并拒绝引号/尖括号，避免后续页面以 `{!! !!}` 原样输出时引入 XSS 风险。
-        $safeBack = (str_starts_with($back, '/') && !preg_match('/["\'<>]/', $back)) ? $back : '';
+        $safeBack = (str_starts_with($back, '/')
+            && !preg_match('/["\'<>]/', $back)
+            // back 本身不应再包含 back（避免无限嵌套导致 URL 膨胀）
+            && !preg_match('/(?:^|[?&])back=/', $back))
+            ? $back
+            : '';
 
         $plan = Plan::query()->create($data);
 
@@ -186,7 +196,12 @@ class PlanController extends Controller
 
         $back = (string) $request->query('back', '');
         // back 需为站内相对路径，并拒绝引号/尖括号，避免后续页面以 `{!! !!}` 原样输出时引入 XSS 风险。
-        $safeBack = (str_starts_with($back, '/') && !preg_match('/["\'<>]/', $back)) ? $back : '';
+        $safeBack = (str_starts_with($back, '/')
+            && !preg_match('/["\'<>]/', $back)
+            // back 本身不应再包含 back（避免无限嵌套导致 URL 膨胀）
+            && !preg_match('/(?:^|[?&])back=/', $back))
+            ? $back
+            : '';
 
         return view('admin.plans.form', [
             'plan' => $plan,
@@ -226,7 +241,12 @@ class PlanController extends Controller
 
         $back = (string) $request->input('back', '');
         // back 需为站内相对路径，并拒绝引号/尖括号，避免后续页面以 `{!! !!}` 原样输出时引入 XSS 风险。
-        $safeBack = (str_starts_with($back, '/') && !preg_match('/["\'<>]/', $back)) ? $back : '';
+        $safeBack = (str_starts_with($back, '/')
+            && !preg_match('/["\'<>]/', $back)
+            // back 本身不应再包含 back（避免无限嵌套导致 URL 膨胀）
+            && !preg_match('/(?:^|[?&])back=/', $back))
+            ? $back
+            : '';
 
         $plan->update($data);
 
diff --git a/app/Http/Controllers/Admin/PlatformOrderController.php b/app/Http/Controllers/Admin/PlatformOrderController.php
index 4e11942..f75ab94 100644
--- a/app/Http/Controllers/Admin/PlatformOrderController.php
+++ b/app/Http/Controllers/Admin/PlatformOrderController.php
@@ -45,7 +45,10 @@ class PlatformOrderController extends Controller
         // back 安全阀：必须为站内相对路径，并拒绝引号/尖括号。
         // 说明：form 页会把 defaults.back 透传到 hidden input 与返回按钮；因此这里提前清洗，避免 unsafe back 在页面中出现。
         $incomingBack = (string) ($defaults['back'] ?? '');
-        $defaults['back'] = (str_starts_with($incomingBack, '/') && !preg_match('/["\'<>]/', $incomingBack))
+        $defaults['back'] = (str_starts_with($incomingBack, '/')
+            && !preg_match('/["\'<>]/', $incomingBack)
+            // back 本身不应再包含 back（避免无限嵌套导致 URL 膨胀）
+            && !preg_match('/(?:^|[?&])back=/', $incomingBack))
             ? $incomingBack
             : '';
 
@@ -134,7 +137,12 @@ class PlatformOrderController extends Controller
 
         $back = (string) ($data['back'] ?? '');
         // back 需为站内相对路径，并拒绝引号/尖括号，避免在后续页面以 `{!! !!}` 原样输出时引入 XSS 风险。
-        $safeBack = (str_starts_with($back, '/') && !preg_match('/["\'<>]/', $back)) ? $back : '';
+        $safeBack = (str_starts_with($back, '/')
+            && !preg_match('/["\'<>]/', $back)
+            // back 本身不应再包含 back（避免无限嵌套导致 URL 膨胀）
+            && !preg_match('/(?:^|[?&])back=/', $back))
+            ? $back
+            : '';
 
         $redirectUrl = '/admin/platform-orders/' . $order->id;
         if ($safeBack !== '') {
diff --git a/tests/Feature/AdminPlanControllerBackValidationTest.php b/tests/Feature/AdminPlanControllerBackValidationTest.php
index c5d68ca..819effd 100644
--- a/tests/Feature/AdminPlanControllerBackValidationTest.php
+++ b/tests/Feature/AdminPlanControllerBackValidationTest.php
@@ -33,6 +33,19 @@ class AdminPlanControllerBackValidationTest extends TestCase
         $res->assertDontSee($unsafeBack, false);
     }
 
+    public function test_create_should_not_echo_back_when_back_contains_nested_back_param(): void
+    {
+        $this->loginAsPlatformAdmin();
+
+        $nestedBack = '/admin/platform-orders?status=pending&back=/admin/plans';
+
+        $res = $this->get('/admin/plans/create?back=' . urlencode($nestedBack));
+        $res->assertOk();
+
+        $res->assertDontSee('name="back"', false);
+        $res->assertDontSee($nestedBack, false);
+    }
+
     public function test_store_should_ignore_unsafe_back_and_redirect_to_index(): void
     {
         $this->loginAsPlatformAdmin();
diff --git a/tests/Feature/AdminPlatformOrderCreateBackValidationTest.php b/tests/Feature/AdminPlatformOrderCreateBackValidationTest.php
index c331288..ba4cc98 100644
--- a/tests/Feature/AdminPlatformOrderCreateBackValidationTest.php
+++ b/tests/Feature/AdminPlatformOrderCreateBackValidationTest.php
@@ -35,4 +35,18 @@ class AdminPlatformOrderCreateBackValidationTest extends TestCase
         // 返回按钮应回退到默认列表
         $res->assertSee('href="/admin/platform-orders"', false);
     }
+
+    public function test_create_should_not_echo_back_when_back_contains_nested_back_param(): void
+    {
+        $this->loginAsPlatformAdmin();
+
+        $nestedBack = '/admin/site-subscriptions?status=activated&back=/admin/platform-orders';
+
+        $res = $this->get('/admin/platform-orders/create?back=' . urlencode($nestedBack));
+        $res->assertOk();
+
+        $res->assertDontSee('name="back"', false);
+        $res->assertDontSee($nestedBack, false);
+        $res->assertSee('href="/admin/platform-orders"', false);
+    }
 }