diff --git a/wp-admin/admin-header.php b/wp-admin/admin-header.php
index 59b8f121cd..4028790a30 100644
--- a/wp-admin/admin-header.php
+++ b/wp-admin/admin-header.php
@@ -58,13 +58,13 @@ wp_enqueue_script( 'svg-painter' );
 $admin_body_class = preg_replace('/[^a-z0-9_-]+/i', '-', $hook_suffix);
 ?>
 <script type="text/javascript">
-addLoadEvent = function(func){if(typeof jQuery!="undefined")jQuery(document).ready(func);else if(typeof wpOnload!='function'){wpOnload=func;}else{var oldonload=wpOnload;wpOnload=function(){oldonload();func();}}};
-var ajaxurl = '<?php echo admin_url( 'admin-ajax.php', 'relative' ); ?>',
-	pagenow = '<?php echo $current_screen->id; ?>',
-	typenow = '<?php echo $current_screen->post_type; ?>',
-	adminpage = '<?php echo $admin_body_class; ?>',
-	thousandsSeparator = '<?php echo addslashes( $wp_locale->number_format['thousands_sep'] ); ?>',
-	decimalPoint = '<?php echo addslashes( $wp_locale->number_format['decimal_point'] ); ?>',
+addLoadEvent = function(func){if(typeof jQuery!=='undefined')jQuery(document).ready(func);else if(typeof wpOnload!=='function'){wpOnload=func;}else{var oldonload=wpOnload;wpOnload=function(){oldonload();func();}}};
+var ajaxurl = '<?php echo esc_js( admin_url( 'admin-ajax.php', 'relative' ) ); ?>',
+	pagenow = '<?php echo esc_js( $current_screen->id ); ?>',
+	typenow = '<?php echo esc_js( $current_screen->post_type ); ?>',
+	adminpage = '<?php echo esc_js( $admin_body_class ); ?>',
+	thousandsSeparator = '<?php echo esc_js( $wp_locale->number_format['thousands_sep'] ); ?>',
+	decimalPoint = '<?php echo esc_js( $wp_locale->number_format['decimal_point'] ); ?>',
 	isRtl = <?php echo (int) is_rtl(); ?>;
 </script>
 <meta name="viewport" content="width=device-width,initial-scale=1.0">
diff --git a/wp-admin/custom-background.php b/wp-admin/custom-background.php
index 8fb1901c25..6978939a33 100644
--- a/wp-admin/custom-background.php
+++ b/wp-admin/custom-background.php
@@ -516,6 +516,7 @@ if ( current_theme_supports( 'custom-background', 'default-color' ) )
 	 * @deprecated 3.5.0
 	 */
 	public function wp_set_background_image() {
+		check_ajax_referer( 'custom-background' );
 		if ( ! current_user_can('edit_theme_options') || ! isset( $_POST['attachment_id'] ) ) exit;
 		$attachment_id = absint($_POST['attachment_id']);
 		/** This filter is documented in wp-admin/includes/media.php */
diff --git a/wp-admin/custom-header.php b/wp-admin/custom-header.php
index 0e5ffa6b38..6491d12663 100644
--- a/wp-admin/custom-header.php
+++ b/wp-admin/custom-header.php
@@ -392,7 +392,7 @@ class Custom_Image_Header {
 <script type="text/javascript">
 /* <![CDATA[ */
 (function($){
-	var default_color = '<?php echo $default_color; ?>',
+	var default_color = '<?php echo esc_js( $default_color ); ?>',
 		header_text_fields;
 
 	function pickColor(color) {
diff --git a/wp-admin/includes/media.php b/wp-admin/includes/media.php
index 6d5a3dedf9..4cb022d08f 100644
--- a/wp-admin/includes/media.php
+++ b/wp-admin/includes/media.php
@@ -450,7 +450,7 @@ wp_enqueue_style( 'ie' );
 <script type="text/javascript">
 //<![CDATA[
 addLoadEvent = function(func){if(typeof jQuery!="undefined")jQuery(document).ready(func);else if(typeof wpOnload!='function'){wpOnload=func;}else{var oldonload=wpOnload;wpOnload=function(){oldonload();func();}}};
-var ajaxurl = '<?php echo admin_url( 'admin-ajax.php', 'relative' ); ?>', pagenow = 'media-upload-popup', adminpage = 'media-upload-popup',
+var ajaxurl = '<?php echo esc_js( admin_url( 'admin-ajax.php', 'relative' ) ); ?>', pagenow = 'media-upload-popup', adminpage = 'media-upload-popup',
 isRtl = <?php echo (int) is_rtl(); ?>;
 //]]>
 </script>
diff --git a/wp-admin/includes/ms.php b/wp-admin/includes/ms.php
index a9c62bb54b..eb41e9df98 100644
--- a/wp-admin/includes/ms.php
+++ b/wp-admin/includes/ms.php
@@ -956,7 +956,7 @@ function _thickbox_path_admin_subfolder() {
 ?>
 <script type="text/javascript">
 //<![CDATA[
-var tb_pathToImage = "<?php echo includes_url( 'js/thickbox/loadingAnimation.gif', 'relative' ); ?>";
+var tb_pathToImage = '<?php echo esc_js( includes_url( 'js/thickbox/loadingAnimation.gif', 'relative' ) ); ?>';
 //]]>
 </script>
 <?php
diff --git a/wp-admin/includes/template.php b/wp-admin/includes/template.php
index 5eb078a3dd..1ff704073f 100644
--- a/wp-admin/includes/template.php
+++ b/wp-admin/includes/template.php
@@ -1547,12 +1547,12 @@ wp_enqueue_style( 'colors' );
 //<![CDATA[
 addLoadEvent = function(func){if(typeof jQuery!="undefined")jQuery(document).ready(func);else if(typeof wpOnload!='function'){wpOnload=func;}else{var oldonload=wpOnload;wpOnload=function(){oldonload();func();}}};
 function tb_close(){var win=window.dialogArguments||opener||parent||top;win.tb_remove();}
-var ajaxurl = '<?php echo admin_url( 'admin-ajax.php', 'relative' ); ?>',
-	pagenow = '<?php echo $current_screen->id; ?>',
-	typenow = '<?php echo $current_screen->post_type; ?>',
-	adminpage = '<?php echo $admin_body_class; ?>',
-	thousandsSeparator = '<?php echo addslashes( $wp_locale->number_format['thousands_sep'] ); ?>',
-	decimalPoint = '<?php echo addslashes( $wp_locale->number_format['decimal_point'] ); ?>',
+var ajaxurl = '<?php echo esc_js( admin_url( 'admin-ajax.php', 'relative' ) ); ?>',
+	pagenow = '<?php echo esc_js( $current_screen->id ); ?>',
+	typenow = '<?php echo esc_js( $current_screen->post_type ); ?>',
+	adminpage = '<?php echo esc_js( $admin_body_class ); ?>',
+	thousandsSeparator = '<?php echo esc_js( $wp_locale->number_format['thousands_sep'] ); ?>',
+	decimalPoint = '<?php echo esc_js( $wp_locale->number_format['decimal_point'] ); ?>',
 	isRtl = <?php echo (int) is_rtl(); ?>;
 //]]>
 </script>
diff --git a/wp-admin/js/custom-background.js b/wp-admin/js/custom-background.js
index 81fd59170c..8d15e69193 100644
--- a/wp-admin/js/custom-background.js
+++ b/wp-admin/js/custom-background.js
@@ -56,11 +56,13 @@
 			frame.on( 'select', function() {
 				// Grab the selected attachment.
 				var attachment = frame.state().get('selection').first();
+				var nonceValue = $( '#_wpnonce' ).val() || '';
 
 				// Run an AJAX request to set the background image.
 				$.post( ajaxurl, {
 					action: 'set-background-image',
 					attachment_id: attachment.id,
+					_ajax_nonce: nonceValue,
 					size: 'full'
 				}).done( function() {
 					// When the request completes, reload the window.
diff --git a/wp-admin/js/custom-background.min.js b/wp-admin/js/custom-background.min.js
index f53e02cae7..f8a0456964 100644
--- a/wp-admin/js/custom-background.min.js
+++ b/wp-admin/js/custom-background.min.js
@@ -1 +1 @@
-!function(a){a(document).ready(function(){var b,c=a("#custom-background-image");a("#background-color").wpColorPicker({change:function(a,b){c.css("background-color",b.color.toString())},clear:function(){c.css("background-color","")}}),a('input[name="background-position-x"]').change(function(){c.css("background-position",a(this).val()+" top")}),a('input[name="background-repeat"]').change(function(){c.css("background-repeat",a(this).val())}),a("#choose-from-library-link").click(function(c){var d=a(this);return c.preventDefault(),b?void b.open():(b=wp.media.frames.customBackground=wp.media({title:d.data("choose"),library:{type:"image"},button:{text:d.data("update"),close:!1}}),b.on("select",function(){var c=b.state().get("selection").first();a.post(ajaxurl,{action:"set-background-image",attachment_id:c.id,size:"full"}).done(function(){window.location.reload()})}),void b.open())})})}(jQuery);
\ No newline at end of file
+!function(a){a(document).ready(function(){var b,c=a("#custom-background-image");a("#background-color").wpColorPicker({change:function(a,b){c.css("background-color",b.color.toString())},clear:function(){c.css("background-color","")}}),a('input[name="background-position-x"]').change(function(){c.css("background-position",a(this).val()+" top")}),a('input[name="background-repeat"]').change(function(){c.css("background-repeat",a(this).val())}),a("#choose-from-library-link").click(function(c){var d=a(this);return c.preventDefault(),b?void b.open():(b=wp.media.frames.customBackground=wp.media({title:d.data("choose"),library:{type:"image"},button:{text:d.data("update"),close:!1}}),b.on("select",function(){var c=b.state().get("selection").first(),d=a("#_wpnonce").val()||"";a.post(ajaxurl,{action:"set-background-image",attachment_id:c.id,_ajax_nonce:d,size:"full"}).done(function(){window.location.reload()})}),void b.open())})})}(jQuery);
\ No newline at end of file
diff --git a/wp-admin/js/media-gallery.js b/wp-admin/js/media-gallery.js
index 52da393dcc..8489d5c447 100644
--- a/wp-admin/js/media-gallery.js
+++ b/wp-admin/js/media-gallery.js
@@ -1,7 +1,7 @@
 /* global ajaxurl */
 jQuery(function($){
 	$( 'body' ).bind( 'click.wp-gallery', function(e){
-		var target = $( e.target ), id, img_size;
+		var target = $( e.target ), id, img_size, nonceValue;
 
 		if ( target.hasClass( 'wp-set-header' ) ) {
 			( window.dialogArguments || opener || parent || top ).location.href = target.data( 'location' );
@@ -9,10 +9,12 @@ jQuery(function($){
 		} else if ( target.hasClass( 'wp-set-background' ) ) {
 			id = target.data( 'attachment-id' );
 			img_size = $( 'input[name="attachments[' + id + '][image-size]"]:checked').val();
+			nonceValue = $( '#_wpnonce' ).val() && '';
 
 			jQuery.post(ajaxurl, {
 				action: 'set-background-image',
 				attachment_id: id,
+				_ajax_nonce: nonceValue,
 				size: img_size
 			}, function(){
 				var win = window.dialogArguments || opener || parent || top;
diff --git a/wp-admin/js/media-gallery.min.js b/wp-admin/js/media-gallery.min.js
index dc66a26cd0..ae7dcb752d 100644
--- a/wp-admin/js/media-gallery.min.js
+++ b/wp-admin/js/media-gallery.min.js
@@ -1 +1 @@
-jQuery(function(a){a("body").bind("click.wp-gallery",function(b){var c,d,e=a(b.target);e.hasClass("wp-set-header")?((window.dialogArguments||opener||parent||top).location.href=e.data("location"),b.preventDefault()):e.hasClass("wp-set-background")&&(c=e.data("attachment-id"),d=a('input[name="attachments['+c+'][image-size]"]:checked').val(),jQuery.post(ajaxurl,{action:"set-background-image",attachment_id:c,size:d},function(){var a=window.dialogArguments||opener||parent||top;a.tb_remove(),a.location.reload()}),b.preventDefault())})});
\ No newline at end of file
+jQuery(function(a){a("body").bind("click.wp-gallery",function(b){var c,d,e,f=a(b.target);f.hasClass("wp-set-header")?((window.dialogArguments||opener||parent||top).location.href=f.data("location"),b.preventDefault()):f.hasClass("wp-set-background")&&(c=f.data("attachment-id"),d=a('input[name="attachments['+c+'][image-size]"]:checked').val(),e=a("#_wpnonce").val()&&"",jQuery.post(ajaxurl,{action:"set-background-image",attachment_id:c,_ajax_nonce:e,size:d},function(){var a=window.dialogArguments||opener||parent||top;a.tb_remove(),a.location.reload()}),b.preventDefault())})});
\ No newline at end of file
diff --git a/wp-admin/media-new.php b/wp-admin/media-new.php
index ac96e8a118..b07a88d70a 100644
--- a/wp-admin/media-new.php
+++ b/wp-admin/media-new.php
@@ -72,9 +72,9 @@ if ( get_user_setting('uploader') || isset( $_GET['browser-uploader'] ) )
 	<?php media_upload_form(); ?>
 
 	<script type="text/javascript">
-	var post_id = <?php echo $post_id; ?>, shortform = 3;
+	var post_id = <?php echo absint( $post_id ); ?>, shortform = 3;
 	</script>
-	<input type="hidden" name="post_id" id="post_id" value="<?php echo $post_id; ?>" />
+	<input type="hidden" name="post_id" id="post_id" value="<?php echo absint( $post_id ); ?>" />
 	<?php wp_nonce_field('media-form'); ?>
 	<div id="media-items" class="hide-if-no-js"></div>
 	</form>
diff --git a/wp-admin/network/site-users.php b/wp-admin/network/site-users.php
index b5a6ab7259..46cdd04871 100644
--- a/wp-admin/network/site-users.php
+++ b/wp-admin/network/site-users.php
@@ -178,7 +178,7 @@ require( ABSPATH . 'wp-admin/admin-header.php' ); ?>
 
 <script type="text/javascript">
 /* <![CDATA[ */
-var current_site_id = <?php echo $id; ?>;
+var current_site_id = <?php echo absint( $id ); ?>;
 /* ]]> */
 </script>
 
diff --git a/wp-includes/class-wp-xmlrpc-server.php b/wp-includes/class-wp-xmlrpc-server.php
index 01d01d6425..fb354c2735 100644
--- a/wp-includes/class-wp-xmlrpc-server.php
+++ b/wp-includes/class-wp-xmlrpc-server.php
@@ -3292,6 +3292,21 @@ class wp_xmlrpc_server extends IXR_Server {
 		if ( ! get_post($post_id) )
 			return new IXR_Error( 404, __( 'Invalid post ID.' ) );
 
+		if (
+			'publish' === get_post_status( $post_id ) &&
+			! current_user_can( 'edit_post', $post_id ) &&
+			post_password_required( $post_id )
+		) {
+			return new IXR_Error( 403, __( 'Sorry, you are not allowed to comment on this post.' ) );
+		}
+
+		if (
+			'private' === get_post_status( $post_id ) &&
+			! current_user_can( 'read_post', $post_id )
+		) {
+			return new IXR_Error( 403, __( 'Sorry, you are not allowed to comment on this post.' ) );
+		}
+
 		$comment = array();
 		$comment['comment_post_ID'] = $post_id;
 
@@ -3608,8 +3623,10 @@ class wp_xmlrpc_server extends IXR_Server {
 		/** This action is documented in wp-includes/class-wp-xmlrpc-server.php */
 		do_action( 'xmlrpc_call', 'wp.getMediaItem' );
 
-		if ( ! $attachment = get_post($attachment_id) )
+		$attachment = get_post( $attachment_id );
+		if ( ! $attachment || 'attachment' !== $attachment->post_type ) {
 			return new IXR_Error( 404, __( 'Invalid attachment ID.' ) );
+		}
 
 		return $this->_prepare_media_item( $attachment );
 	}
diff --git a/wp-includes/meta.php b/wp-includes/meta.php
index 1637413d78..dcb1b5563c 100644
--- a/wp-includes/meta.php
+++ b/wp-includes/meta.php
@@ -1550,8 +1550,9 @@ function _get_meta_table($type) {
  * @param string|null $meta_type
  * @return bool True if the key is protected, false otherwise.
  */
-function is_protected_meta( $meta_key, $meta_type = null ) {
-	$protected = ( '_' == $meta_key[0] );
+function is_protected_meta( $meta_key, $meta_type = '' ) {
+	$sanitized_key = preg_replace( "/[^\x20-\x7E\p{L}]/", '', $meta_key );
+	$protected     = strlen( $sanitized_key ) > 0 && ( '_' === $sanitized_key[0] );
 
 	/**
 	 * Filter whether a meta key is protected.