diff --git a/app/code/Magento/Captcha/Controller/Adminhtml/Refresh/Refresh.php b/app/code/Magento/Captcha/Controller/Adminhtml/Refresh/Refresh.php
index 9c7ccc0983db7..47e0103dd1907 100644
--- a/app/code/Magento/Captcha/Controller/Adminhtml/Refresh/Refresh.php
+++ b/app/code/Magento/Captcha/Controller/Adminhtml/Refresh/Refresh.php
@@ -10,13 +10,39 @@
 
 class Refresh extends \Magento\Backend\App\Action
 {
+    /**
+     * @var \Magento\Framework\Serialize\Serializer\Json
+     */
+    protected $serializer;
+
+    /**
+     * @var \Magento\Captcha\Helper\Data
+     */
+    protected $captchaHelper;
+
+    /**
+     * Refresh constructor.
+     * @param \Magento\Backend\App\Action\Context $context
+     * @param \Magento\Captcha\Helper\Data $captchaHelper
+     * @param \Magento\Framework\Serialize\Serializer\Json $serializer
+     */
+    public function __construct(
+        \Magento\Backend\App\Action\Context $context,
+        \Magento\Captcha\Helper\Data $captchaHelper,
+        \Magento\Framework\Serialize\Serializer\Json $serializer
+    ) {
+        parent::__construct($context);
+        $this->serializer = $serializer;
+        $this->captchaHelper = $captchaHelper;
+    }
+
     /**
      * {@inheritdoc}
      */
     public function execute()
     {
         $formId = $this->getRequest()->getPost('formId');
-        $captchaModel = $this->_objectManager->get(\Magento\Captcha\Helper\Data::class)->getCaptcha($formId);
+        $captchaModel = $this->captchaHelper->getCaptcha($formId);
         $this->_view->getLayout()->createBlock(
             $captchaModel->getBlockName()
         )->setFormId(
@@ -24,7 +50,7 @@ public function execute()
         )->setIsAjax(
             true
         )->toHtml();
-        $this->getResponse()->representJson(json_encode(['imgSrc' => $captchaModel->getImgSrc()]));
+        $this->getResponse()->representJson($this->serializer->serialize(['imgSrc' => $captchaModel->getImgSrc()]));
         $this->_actionFlag->set('', self::FLAG_NO_POST_DISPATCH, true);
     }
 
diff --git a/app/code/Magento/Captcha/Controller/Refresh/Index.php b/app/code/Magento/Captcha/Controller/Refresh/Index.php
index 0124adc348bb7..ef757d1b2fc35 100644
--- a/app/code/Magento/Captcha/Controller/Refresh/Index.php
+++ b/app/code/Magento/Captcha/Controller/Refresh/Index.php
@@ -17,13 +17,25 @@ class Index extends \Magento\Framework\App\Action\Action
      */
     protected $captchaHelper;
 
+    /**
+     * @var \Magento\Framework\Serialize\Serializer\Json
+     */
+    protected $serializer;
+
     /**
      * @param Context $context
      * @param \Magento\Captcha\Helper\Data $captchaHelper
+     * @param \Magento\Framework\Serialize\Serializer\Json|null $serializer
+     * @throws \RuntimeException
      */
-    public function __construct(Context $context, \Magento\Captcha\Helper\Data $captchaHelper)
-    {
+    public function __construct(
+        Context $context,
+        \Magento\Captcha\Helper\Data $captchaHelper,
+        \Magento\Framework\Serialize\Serializer\Json $serializer = null
+    ) {
         $this->captchaHelper = $captchaHelper;
+        $this->serializer = $serializer ?: \Magento\Framework\App\ObjectManager::getInstance()
+            ->get(\Magento\Framework\Serialize\Serializer\Json::class);
         parent::__construct($context);
     }
 
@@ -34,23 +46,19 @@ public function execute()
     {
         $formId = $this->_request->getPost('formId');
         if (null === $formId) {
-            try {
-                $params = [];
-                $content = $this->_request->getContent();
-                if ($content) {
-                    $params = \Zend_Json::decode($content);
-                }
-                $formId = isset($params['formId']) ? $params['formId'] : null;
-            } catch (\Zend_Json_Exception $exception) {
-                $formId = null;
+            $params = [];
+            $content = $this->_request->getContent();
+            if ($content) {
+                $params = $this->serializer->unserialize($content);
             }
+            $formId = isset($params['formId']) ? $params['formId'] : null;
         }
         $captchaModel = $this->captchaHelper->getCaptcha($formId);
         $captchaModel->generate();
 
         $block = $this->_view->getLayout()->createBlock($captchaModel->getBlockName());
         $block->setFormId($formId)->setIsAjax(true)->toHtml();
-        $this->_response->representJson(json_encode(['imgSrc' => $captchaModel->getImgSrc()]));
+        $this->_response->representJson($this->serializer->serialize(['imgSrc' => $captchaModel->getImgSrc()]));
         $this->_actionFlag->set('', self::FLAG_NO_POST_DISPATCH, true);
     }
 }
diff --git a/app/code/Magento/Captcha/Model/Customer/Plugin/AjaxLogin.php b/app/code/Magento/Captcha/Model/Customer/Plugin/AjaxLogin.php
index d2f3cbda170b4..a21c007056e73 100644
--- a/app/code/Magento/Captcha/Model/Customer/Plugin/AjaxLogin.php
+++ b/app/code/Magento/Captcha/Model/Customer/Plugin/AjaxLogin.php
@@ -26,6 +26,11 @@ class AjaxLogin
      */
     protected $resultJsonFactory;
 
+    /**
+     * @var \Magento\Framework\Serialize\Serializer\Json
+     */
+    protected $serializer;
+
     /**
      * @var array
      */
@@ -36,16 +41,21 @@ class AjaxLogin
      * @param SessionManagerInterface $sessionManager
      * @param JsonFactory $resultJsonFactory
      * @param array $formIds
+     * @param \Magento\Framework\Serialize\Serializer\Json|null $serializer
+     * @throws \RuntimeException
      */
     public function __construct(
         CaptchaHelper $helper,
         SessionManagerInterface $sessionManager,
         JsonFactory $resultJsonFactory,
-        array $formIds
+        array $formIds,
+        \Magento\Framework\Serialize\Serializer\Json $serializer = null
     ) {
         $this->helper = $helper;
         $this->sessionManager = $sessionManager;
         $this->resultJsonFactory = $resultJsonFactory;
+        $this->serializer = $serializer ?: \Magento\Framework\App\ObjectManager::getInstance()
+            ->get(\Magento\Framework\Serialize\Serializer\Json::class);
         $this->formIds = $formIds;
     }
 
@@ -53,7 +63,6 @@ public function __construct(
      * @param \Magento\Customer\Controller\Ajax\Login $subject
      * @param \Closure $proceed
      * @return $this
-     * @throws \Zend_Json_Exception
      * @SuppressWarnings(PHPMD.NPathComplexity)
      * @SuppressWarnings(PHPMD.CyclomaticComplexity)
      */
@@ -70,7 +79,7 @@ public function aroundExecute(
         $loginParams = [];
         $content = $request->getContent();
         if ($content) {
-            $loginParams = \Zend_Json::decode($content);
+            $loginParams = $this->serializer->unserialize($content);
         }
         $username = isset($loginParams['username']) ? $loginParams['username'] : null;
         $captchaString = isset($loginParams[$captchaInputName]) ? $loginParams[$captchaInputName] : null;
diff --git a/app/code/Magento/Captcha/Test/Unit/Controller/Refresh/IndexTest.php b/app/code/Magento/Captcha/Test/Unit/Controller/Refresh/IndexTest.php
index a99ec53ab2400..5fcb4c4fe8828 100644
--- a/app/code/Magento/Captcha/Test/Unit/Controller/Refresh/IndexTest.php
+++ b/app/code/Magento/Captcha/Test/Unit/Controller/Refresh/IndexTest.php
@@ -47,6 +47,11 @@ class IndexTest extends \PHPUnit_Framework_TestCase
      */
     protected $flagMock;
 
+    /**
+     * @var \PHPUnit_Framework_MockObject_MockObject
+     */
+    protected $serializerMock;
+
     /**
      * @var \Magento\Captcha\Controller\Refresh\Index
      */
@@ -62,6 +67,13 @@ protected function setUp()
         $this->viewMock = $this->getMock(\Magento\Framework\App\ViewInterface::class);
         $this->layoutMock = $this->getMock(\Magento\Framework\View\LayoutInterface::class);
         $this->flagMock = $this->getMock(\Magento\Framework\App\ActionFlag::class, [], [], '', false);
+        $this->serializerMock = $this->getMock(
+            \Magento\Framework\Serialize\Serializer\Json::class,
+            [],
+            [],
+            '',
+            false
+        );
 
         $this->contextMock->expects($this->any())->method('getRequest')->will($this->returnValue($this->requestMock));
         $this->contextMock->expects($this->any())->method('getView')->will($this->returnValue($this->viewMock));
@@ -69,17 +81,23 @@ protected function setUp()
         $this->contextMock->expects($this->any())->method('getActionFlag')->will($this->returnValue($this->flagMock));
         $this->viewMock->expects($this->any())->method('getLayout')->will($this->returnValue($this->layoutMock));
 
-        $this->model = new \Magento\Captcha\Controller\Refresh\Index($this->contextMock, $this->captchaHelperMock);
+        $this->model = new \Magento\Captcha\Controller\Refresh\Index(
+            $this->contextMock,
+            $this->captchaHelperMock,
+            $this->serializerMock
+        );
     }
 
     /**
      * @dataProvider executeDataProvider
      * @param int $formId
      * @param int $callsNumber
+     * @throws \PHPUnit_Framework_Exception
      */
     public function testExecute($formId, $callsNumber)
     {
         $content = ['formId' => $formId];
+        $imgSource = ['imgSrc' => 'source'];
 
         $blockMethods = ['setFormId', 'setIsAjax', 'toHtml'];
         $blockMock = $this->getMock(\Magento\Captcha\Block\Captcha::class, $blockMethods, [], '', false);
@@ -97,8 +115,12 @@ public function testExecute($formId, $callsNumber)
         $blockMock->expects($this->any())->method('setFormId')->with($formId)->will($this->returnValue($blockMock));
         $blockMock->expects($this->any())->method('setIsAjax')->with(true)->will($this->returnValue($blockMock));
         $blockMock->expects($this->once())->method('toHtml');
-        $this->responseMock->expects($this->once())->method('representJson')->with(json_encode(['imgSrc' => 'source']));
+        $this->responseMock->expects($this->once())->method('representJson')->with(json_encode($imgSource));
         $this->flagMock->expects($this->once())->method('set')->with('', 'no-postDispatch', true);
+        $this->serializerMock->expects($this->exactly($callsNumber))
+            ->method('unserialize')->will($this->returnValue($content));
+        $this->serializerMock->expects($this->once())
+            ->method('serialize')->will($this->returnValue(json_encode($imgSource)));
 
         $this->model->execute();
     }
diff --git a/app/code/Magento/Captcha/Test/Unit/Model/Customer/Plugin/AjaxLoginTest.php b/app/code/Magento/Captcha/Test/Unit/Model/Customer/Plugin/AjaxLoginTest.php
index 8047138e34528..858b4bc8d9ebc 100644
--- a/app/code/Magento/Captcha/Test/Unit/Model/Customer/Plugin/AjaxLoginTest.php
+++ b/app/code/Magento/Captcha/Test/Unit/Model/Customer/Plugin/AjaxLoginTest.php
@@ -42,6 +42,11 @@ class AjaxLoginTest extends \PHPUnit_Framework_TestCase
      */
     protected $loginControllerMock;
 
+    /**
+     * @var \PHPUnit_Framework_MockObject_MockObject
+     */
+    protected $serializerMock;
+
     /**
      * @var array
      */
@@ -79,12 +84,20 @@ protected function setUp()
         $this->captchaHelperMock->expects($this->once())->method('getCaptcha')
             ->with('user_login')->will($this->returnValue($this->captchaMock));
         $this->formIds = ['user_login'];
+        $this->serializerMock = $this->getMock(
+            \Magento\Framework\Serialize\Serializer\Json::class,
+            [],
+            [],
+            '',
+            false
+        );
 
         $this->model = new \Magento\Captcha\Model\Customer\Plugin\AjaxLogin(
             $this->captchaHelperMock,
             $this->sessionManagerMock,
             $this->jsonFactoryMock,
-            $this->formIds
+            $this->formIds,
+            $this->serializerMock
         );
     }
 
@@ -92,11 +105,12 @@ public function testAroundExecute()
     {
         $username = 'name';
         $captchaString = 'string';
-        $requestContent = json_encode([
+        $requestData = [
             'username' => $username,
             'captcha_string' => $captchaString,
             'captcha_form_id' => $this->formIds[0]
-        ]);
+        ];
+        $requestContent = json_encode($requestData);
 
         $this->requestMock->expects($this->once())->method('getContent')->will($this->returnValue($requestContent));
         $this->captchaMock->expects($this->once())->method('isRequired')->with($username)
@@ -104,6 +118,7 @@ public function testAroundExecute()
         $this->captchaMock->expects($this->once())->method('logAttempt')->with($username);
         $this->captchaMock->expects($this->once())->method('isCorrect')->with($captchaString)
             ->will($this->returnValue(true));
+        $this->serializerMock->expects(($this->once()))->method('unserialize')->will($this->returnValue($requestData));
 
         $closure = function () {
             return 'result';
@@ -115,11 +130,12 @@ public function testAroundExecuteIncorrectCaptcha()
     {
         $username = 'name';
         $captchaString = 'string';
-        $requestContent = json_encode([
+        $requestData = [
             'username' => $username,
             'captcha_string' => $captchaString,
             'captcha_form_id' => $this->formIds[0]
-        ]);
+        ];
+        $requestContent = json_encode($requestData);
 
         $this->requestMock->expects($this->once())->method('getContent')->will($this->returnValue($requestContent));
         $this->captchaMock->expects($this->once())->method('isRequired')->with($username)
@@ -127,6 +143,7 @@ public function testAroundExecuteIncorrectCaptcha()
         $this->captchaMock->expects($this->once())->method('logAttempt')->with($username);
         $this->captchaMock->expects($this->once())->method('isCorrect')
             ->with($captchaString)->will($this->returnValue(false));
+        $this->serializerMock->expects(($this->once()))->method('unserialize')->will($this->returnValue($requestData));
 
         $this->sessionManagerMock->expects($this->once())->method('setUsername')->with($username);
         $this->jsonFactoryMock->expects($this->once())->method('create')
@@ -147,7 +164,10 @@ public function testAroundExecuteIncorrectCaptcha()
      */
     public function testAroundExecuteCaptchaIsNotRequired($username, $requestContent)
     {
-        $this->requestMock->expects($this->once())->method('getContent')->will($this->returnValue($requestContent));
+        $this->requestMock->expects($this->once())->method('getContent')
+            ->will($this->returnValue(json_encode($requestContent)));
+        $this->serializerMock->expects(($this->once()))->method('unserialize')
+            ->will($this->returnValue($requestContent));
 
         $this->captchaMock->expects($this->once())->method('isRequired')->with($username)
             ->will($this->returnValue(false));
@@ -168,11 +188,11 @@ public function aroundExecuteCaptchaIsNotRequired()
         return [
             [
                 'username' => 'name',
-                'requestContent' => json_encode(['username' => 'name', 'captcha_string' => 'string']),
+                'requestData' => ['username' => 'name', 'captcha_string' => 'string'],
             ],
             [
                 'username' => null,
-                'requestContent' => json_encode(['captcha_string' => 'string']),
+                'requestData' => ['captcha_string' => 'string'],
             ],
         ];
     }