diff --git a/framework/yii/assets/yii.js b/framework/yii/assets/yii.js
index 99a314e..22f92a5 100644
--- a/framework/yii/assets/yii.js
+++ b/framework/yii/assets/yii.js
@@ -163,6 +163,12 @@ yii = (function ($) {
 		init: function () {
 			var $document = $(document);
 
+			$.ajaxPrefilter(function (options, originalOptions, xhr) {
+				if (!options.crossDomain && pub.getCsrfVar()) {
+					xhr.setRequestHeader('X-CSRF-TOKEN', pub.getCsrfToken());
+				}
+			});
+
 			$document.on('click.yii', pub.clickableSelector, function (event) {
 				var $this = $(this);
 				if (pub.allowAction($this)) {
diff --git a/framework/yii/web/Request.php b/framework/yii/web/Request.php
index a07deaa..76c8883 100644
--- a/framework/yii/web/Request.php
+++ b/framework/yii/web/Request.php
@@ -76,7 +76,7 @@ class Request extends \yii\base\Request
 	const CSRF_HEADER = 'X-CSRF-TOKEN';
 
 	/**
-	 * @var boolean whether to enable CSRF (Cross-Site Request Forgery) validation. Defaults to false.
+	 * @var boolean whether to enable CSRF (Cross-Site Request Forgery) validation. Defaults to true.
 	 * When CSRF validation is enabled, forms submitted to an Yii Web application must be originated
 	 * from the same application. If not, a 400 HTTP exception will be raised.
 	 *
@@ -90,7 +90,7 @@ class Request extends \yii\base\Request
 	 * @see Controller::enableCsrfValidation
 	 * @see http://en.wikipedia.org/wiki/Cross-site_request_forgery
 	 */
-	public $enableCsrfValidation = false;
+	public $enableCsrfValidation = true;
 	/**
 	 * @var string the name of the token used to prevent CSRF. Defaults to '_csrf'.
 	 * This property is used only when [[enableCsrfValidation]] is true.