diff --git a/Config/config.php b/Config/config.php
index fea80efa2..add337b95 100644
--- a/Config/config.php
+++ b/Config/config.php
@@ -637,6 +637,9 @@
             ],
         ],
         'events' => [
+            'custom_objects.api_platform.permission_context.subscriber' => [
+                'class' => \MauticPlugin\CustomObjectsBundle\EventListener\ApiPlatformPermissionContextSubscriber::class,
+            ],
             'custom_object.api.subscriber' => [
                 'class'     => \MauticPlugin\CustomObjectsBundle\EventListener\ApiSubscriber::class,
                 'arguments' => [
diff --git a/EventListener/ApiPlatformPermissionContextSubscriber.php b/EventListener/ApiPlatformPermissionContextSubscriber.php
new file mode 100644
index 000000000..1c5d073d0
--- /dev/null
+++ b/EventListener/ApiPlatformPermissionContextSubscriber.php
@@ -0,0 +1,118 @@
+<?php
+
+declare(strict_types=1);
+
+namespace MauticPlugin\CustomObjectsBundle\EventListener;
+
+use Symfony\Component\EventDispatcher\EventSubscriberInterface;
+use Symfony\Component\HttpFoundation\Request;
+
+final class ApiPlatformPermissionContextSubscriber implements EventSubscriberInterface
+{
+    public static function getSubscribedEvents(): array
+    {
+        return [
+            'mautic.api_platform_permission_context' => ['onApiPlatformPermissionContext', 0],
+        ];
+    }
+
+    /*
+     * Note, the new ApiPlatformPermissionContextEvent will be available in Mautic 7.
+     * Till then we have to go with a plain object type.
+     */
+    public function onApiPlatformPermissionContext(object $event): void
+    {
+        if (!method_exists($event, 'getPermission')
+            || !method_exists($event, 'setPermission')
+            || !method_exists($event, 'getRequestObject')
+            || !method_exists($event, 'setRequestObject')
+        ) {
+            return;
+        }
+
+        $permission = $event->getPermission();
+        if (!is_string($permission) || 0 !== strpos($permission, 'custom_objects:')) {
+            return;
+        }
+
+        if (false === strpos($permission, '[') && false === strpos($permission, '(')) {
+            return;
+        }
+
+        $requestObject = $event->getRequestObject();
+        $objectPath    = $this->extractObjectPath($permission);
+
+        if (null !== $objectPath) {
+            $requestObject = $this->resolveRequestObject($requestObject, $objectPath);
+            $permission    = substr($permission, 0, strpos($permission, '('));
+        }
+
+        $event->setRequestObject($requestObject);
+        $event->setPermission($this->resolvePermissionPlaceholder($event, $requestObject, $permission));
+    }
+
+    private function extractObjectPath(string $permission): ?string
+    {
+        if (1 !== preg_match('#\((.*?)\)#', $permission, $match)) {
+            return null;
+        }
+
+        if (!isset($match[1]) || '' === $match[1]) {
+            return null;
+        }
+
+        return $match[1];
+    }
+
+    private function resolveRequestObject(mixed $requestObject, string $objectPath): mixed
+    {
+        foreach (explode('.', $objectPath) as $property) {
+            if (!is_object($requestObject) || !method_exists($requestObject, $property)) {
+                return $requestObject;
+            }
+
+            $requestObject = $requestObject->$property();
+        }
+
+        return $requestObject;
+    }
+
+    private function resolvePermissionPlaceholder(object $event, mixed $requestObject, string $permission): string
+    {
+        if (1 !== preg_match('#\[(.*?)\]#', $permission, $match)) {
+            return $permission;
+        }
+
+        if (!isset($match[1]) || '' === $match[1]) {
+            return $permission;
+        }
+
+        $property = $match[1];
+        $objectId = null;
+        $request  = method_exists($event, 'getRequest') ? $event->getRequest() : null;
+        $content  = $request instanceof Request ? json_decode($request->getContent(), true) : null;
+
+        if (is_array($content) && array_key_exists($property, $content)) {
+            $objectId = $content[$property];
+        } elseif (is_object($requestObject)) {
+            $getter = 'get'.ucfirst($property);
+            if (method_exists($requestObject, $getter)) {
+                $objectId = $requestObject->$getter();
+            }
+        }
+
+        if (is_object($objectId) && method_exists($objectId, 'getId')) {
+            $objectId = $objectId->getId();
+        }
+
+        if (is_string($objectId) && false !== strrpos($objectId, '/')) {
+            $objectId = substr($objectId, strrpos($objectId, '/') + 1);
+        }
+
+        if (null === $objectId || '' === $objectId) {
+            return $permission;
+        }
+
+        return preg_replace('#\[(.*?)\]#', (string) $objectId, $permission, 1) ?? $permission;
+    }
+}
diff --git a/Tests/Functional/ApiPlatform/CustomFieldOptionFunctionalTest.php b/Tests/Functional/ApiPlatform/CustomFieldOptionFunctionalTest.php
index 81d331717..e182f70ba 100644
--- a/Tests/Functional/ApiPlatform/CustomFieldOptionFunctionalTest.php
+++ b/Tests/Functional/ApiPlatform/CustomFieldOptionFunctionalTest.php
@@ -13,6 +13,13 @@
 
 final class CustomFieldOptionFunctionalTest extends AbstractApiPlatformFunctionalTest
 {
+    public function setUp(): void
+    {
+        $this->configParams['custom_objects_enabled'] = true;
+
+        parent::setUp();
+    }
+
     public function testCustomFieldOptionCRUD(): void
     {
         foreach ($this->getCRUDProvider() as $parameters) {
@@ -148,8 +155,8 @@ private function getCRUDProvider(): array
                     Response::HTTP_CREATED,
                     Response::HTTP_OK,
                     'New Custom Field Option',
-                    Response::HTTP_FORBIDDEN,
-                    null,
+                    Response::HTTP_OK,
+                    'Edited Custom Field Option',
                     Response::HTTP_NO_CONTENT,
                 ],
             'no_create' => [
diff --git a/Tests/Functional/ApiPlatform/CustomItemFunctionalTest.php b/Tests/Functional/ApiPlatform/CustomItemFunctionalTest.php
index 0a7594a93..fc7a1f7b9 100644
--- a/Tests/Functional/ApiPlatform/CustomItemFunctionalTest.php
+++ b/Tests/Functional/ApiPlatform/CustomItemFunctionalTest.php
@@ -70,6 +70,108 @@ public function getCustomItemsDataProvider(): iterable
         yield [['viewown', 'editown', 'create', 'deleteown', 'publishown'], Response::HTTP_FORBIDDEN];
     }
 
+    public function testGetCustomItemDeniesOwnPermissionForOtherUsersItem(): void
+    {
+        $user = $this->getUser();
+
+        self::assertNotNull($user);
+
+        $customItem = $this->createCustomItem(['viewown'], false, $user->getId() + 9999);
+        $response   = $this->retrieveEntity('/api/v2/custom_items/'.$customItem->getId());
+        $json       = json_decode($response->getContent(), true);
+
+        self::assertSame(Response::HTTP_FORBIDDEN, $response->getStatusCode());
+        $this->assertAccessForbiddenContent($json);
+    }
+
+    /**
+     * @dataProvider ownedCustomItemOperationsDataProvider
+     *
+     * @param array<int, string> $permissions
+     */
+    public function testOwnedCustomItemAllowsOwnScopedOperations(callable $operation, callable $assertion, array $permissions, int $expectedResponse): void
+    {
+        $customItem = $this->createCustomItem($permissions, true);
+
+        $response = $operation($this, $customItem);
+
+        self::assertSame($expectedResponse, $response->getStatusCode());
+
+        $assertion($this, $response, $customItem);
+    }
+
+    /**
+     * @return iterable<int, array{callable, callable, array<int, string>, int}>
+     */
+    public function ownedCustomItemOperationsDataProvider(): iterable
+    {
+        $getOperation = static fn (self $test, CustomItem $customItem): Response => $test->retrieveEntity('/api/v2/custom_items/'.$customItem->getId());
+        $putOperation = static fn (self $test, CustomItem $customItem): Response => $test->updateEntity('/api/v2/custom_items/'.$customItem->getId(), [
+            'name'         => 'Custom Item Edited',
+            'fieldValues'  => [
+                [
+                    'id'    => '/api/v2/custom_fields/'.$customItem->getCustomObject()->getCustomFields()->first()->getId(),
+                    'value' => 'test3',
+                ],
+            ],
+        ]);
+        $patchOperation = static fn (self $test, CustomItem $customItem): Response => $test->patchEntity('/api/v2/custom_items/'.$customItem->getId(), [
+            'fieldValues'  => [
+                [
+                    'id'    => '/api/v2/custom_fields/'.$customItem->getCustomObject()->getCustomFields()->first()->getId(),
+                    'value' => 'test2',
+                ],
+            ],
+        ]);
+        $deleteOperation = static fn (self $test, CustomItem $customItem): Response => $test->deleteEntity('/api/v2/custom_items/'.$customItem->getId());
+
+        $forbiddenAssertion = static function (self $test, Response $response): void {
+            $json = json_decode($response->getContent(), true);
+            $test->assertAccessForbiddenContent($json);
+        };
+        $getSuccessAssertion = static function (self $test, Response $response, CustomItem $customItem): void {
+            $json = json_decode($response->getContent(), true);
+            $test->assertSuccessContent($json, $customItem);
+        };
+        $writeSuccessAssertion = static function (self $test, Response $response, CustomItem $customItem): void {
+            $json = json_decode($response->getContent(), true);
+            $test->em->clear();
+            $customItem = $test->em->getRepository(CustomItem::class)->find($customItem->getId());
+            $test->customItemModel->populateCustomFields($customItem);
+            $test->assertSuccessContent($json, $customItem);
+        };
+        $deleteSuccessAssertion = static function (self $test, Response $response, CustomItem $customItem): void {
+            $json = json_decode($response->getContent(), true);
+            $test->em->clear();
+            self::assertNull($json);
+            self::assertNull($test->em->getRepository(CustomItem::class)->find($customItem->getId()));
+        };
+
+        yield [$getOperation, $getSuccessAssertion, ['viewown'], Response::HTTP_OK];
+
+        yield [$getOperation, $forbiddenAssertion, [], Response::HTTP_FORBIDDEN];
+
+        yield [$getOperation, $getSuccessAssertion, ['viewown', 'viewother'], Response::HTTP_OK];
+
+        yield [$putOperation, $writeSuccessAssertion, ['editown'], Response::HTTP_OK];
+
+        yield [$putOperation, $forbiddenAssertion, ['editother'], Response::HTTP_FORBIDDEN];
+
+        yield [$putOperation, $writeSuccessAssertion, ['editown', 'editother'], Response::HTTP_OK];
+
+        yield [$patchOperation, $writeSuccessAssertion, ['editown'], Response::HTTP_OK];
+
+        yield [$patchOperation, $forbiddenAssertion, ['editother'], Response::HTTP_FORBIDDEN];
+
+        yield [$patchOperation, $writeSuccessAssertion, ['editown', 'editother'], Response::HTTP_OK];
+
+        yield [$deleteOperation, $deleteSuccessAssertion, ['deleteown'], Response::HTTP_NO_CONTENT];
+
+        yield [$deleteOperation, $forbiddenAssertion, ['deleteother'], Response::HTTP_FORBIDDEN];
+
+        yield [$deleteOperation, $deleteSuccessAssertion, ['deleteown', 'deleteother'], Response::HTTP_NO_CONTENT];
+    }
+
     /**
      * @dataProvider postCustomItemsDataProvider
      *
@@ -257,22 +359,29 @@ private function createCustomObject(): CustomObject
     /**
      * @param array<int, string> $permissions
      */
-    private function createCustomItem(array $permissions): CustomItem
+    private function createCustomItem(array $permissions, bool $ownedByCurrentUser = false, ?int $ownerId = null): CustomItem
     {
         $customObject = $this->createCustomObject();
         $category     = $this->createCategory();
         $customField  = $this->createCustomField($customObject);
+        $user         = $this->getUser();
         $customItem   = new CustomItem($customObject);
         $customItem->setName('Custom Item');
         $customItem->setLanguage('en');
         $customItem->setCategory($category);
+
+        if ($ownedByCurrentUser && null !== $user) {
+            $customItem->setCreatedBy($user);
+        } elseif (null !== $ownerId) {
+            $customItem->setCreatedBy($ownerId);
+        }
+
         $customFieldValue = new CustomFieldValueText($customField, $customItem, 'value');
         $customItem->addCustomFieldValue($customFieldValue);
 
         $this->em->persist($customItem);
         $this->em->flush();
 
-        $user = $this->getUser();
         $this->setPermission($user, 'custom_objects:'.$customObject->getId(), $permissions);
 
         return $customItem;