diff --git a/app/Http/Controllers/Api/AssetsController.php b/app/Http/Controllers/Api/AssetsController.php
index 160f4a120a20..8260cacf1021 100644
--- a/app/Http/Controllers/Api/AssetsController.php
+++ b/app/Http/Controllers/Api/AssetsController.php
@@ -9,6 +9,7 @@
 use App\Models\AccessoryCheckout;
 use App\Models\CheckoutAcceptance;
 use App\Models\LicenseSeat;
+use App\Rules\FlatArray;
 use Illuminate\Database\Eloquent\Builder;
 use Illuminate\Http\JsonResponse;
 use Illuminate\Support\Facades\Crypt;
@@ -34,8 +35,6 @@
 use Illuminate\Support\Facades\Route;
 use App\View\Label;
 use Illuminate\Support\Facades\Storage;
-use Illuminate\Support\Facades\Validator;
-
 
 /**
  * This class controls all actions related to assets for
@@ -57,7 +56,12 @@ class AssetsController extends Controller
      */
     public function index(Request $request, $action = null, $upcoming_status = null) : JsonResponse | array
     {
-
+        $request->validate([
+            'filter' => [
+                'json',
+                new FlatArray,
+            ],
+        ]);
 
         // This handles the legacy audit endpoints :(
         if ($action == 'audit') {
diff --git a/app/Rules/FlatArray.php b/app/Rules/FlatArray.php
new file mode 100644
index 000000000000..75537df33603
--- /dev/null
+++ b/app/Rules/FlatArray.php
@@ -0,0 +1,32 @@
+<?php
+
+namespace App\Rules;
+
+use Closure;
+use Illuminate\Contracts\Validation\ValidationRule;
+
+/**
+ * Validates array is only one level deep.
+ * Passes: ['a' => 'b']
+ * Fails: ['a' => ['b', 'c']]
+ */
+class FlatArray implements ValidationRule
+{
+    /**
+     * Run the validation rule.
+     *
+     * @param  \Closure(string, ?string=): \Illuminate\Translation\PotentiallyTranslatedString  $fail
+     */
+    public function validate(string $attribute, mixed $value, Closure $fail): void
+    {
+        if (is_string($value)) {
+            $value = json_decode($value, true);
+        }
+
+        foreach ($value as $arrayValue) {
+            if (is_array($arrayValue)) {
+                $fail(":attribute cannot contain a nested data.");
+            }
+        }
+    }
+}
diff --git a/tests/Feature/Assets/Api/AssetIndexTest.php b/tests/Feature/Assets/Api/AssetIndexTest.php
index 8554edb3d459..d6197e231f0e 100644
--- a/tests/Feature/Assets/Api/AssetIndexTest.php
+++ b/tests/Feature/Assets/Api/AssetIndexTest.php
@@ -7,6 +7,7 @@
 use App\Models\User;
 use Carbon\Carbon;
 use Illuminate\Testing\Fluent\AssertableJson;
+use PHPUnit\Framework\Attributes\DataProvider;
 use Tests\TestCase;
 
 class AssetIndexTest extends TestCase
@@ -126,6 +127,47 @@ public function testAssetApiIndexReturnsDueOrOverdueForExpectedCheckin()
             ->assertJson(fn(AssertableJson $json) => $json->has('rows', 5)->etc());
     }
 
+    public static function filterValues()
+    {
+        return [
+            ['filter%5Bassigned_to%5D'],
+            ['filter[assigned_to][not]=null'],
+            ['filter={%22assigned_to%22:{%22$ne%22:null}}'],
+            ['filter=%5B%22a%22%20%3D%3E%20%22b%22%5D'],
+        ];
+    }
+
+    /**
+     * [RB-17904]
+     * [RB-19910]
+     */
+    #[DataProvider('filterValues')]
+    public function test_handles_non_string_filter($filterString)
+    {
+        $this->actingAsForApi(User::factory()->superuser()->create())
+            ->getJson(route('api.assets.index') . '?' . $filterString)
+            ->assertOk()
+            ->assertStatusMessageIs('error')
+            ->assertMessagesContains('filter');
+    }
+
+    public function test_can_filter_results()
+    {
+        Asset::factory()->create(['purchase_date' => '2025-07-01', 'order_number' => '123']);
+        Asset::factory()->create(['purchase_date' => '2025-07-01', 'order_number' => '123']);
+        Asset::factory()->create(['purchase_date' => '2025-07-01', 'order_number' => '456']);
+
+        $this->actingAsForApi(User::factory()->superuser()->create())
+            ->getJson(route('api.assets.index', [
+                'filter' => json_encode([
+                    'order_number' => '123',
+                    'purchase_date' => '2025-07-01',
+                ]),
+            ]))
+            ->assertOk()
+            ->assertJson(fn(AssertableJson $json) => $json->has('rows', 2)->etc());
+    }
+
     public function testAssetApiIndexAdheresToCompanyScoping()
     {
         [$companyA, $companyB] = Company::factory()->count(2)->create();