diff --git a/wp-admin/about.php b/wp-admin/about.php
index 3d9736bc97..9cd8b4e72c 100644
--- a/wp-admin/about.php
+++ b/wp-admin/about.php
@@ -36,6 +36,26 @@ include( ABSPATH . 'wp-admin/admin-header.php' );
 
 		<div class="changelog point-releases">
 			<h3><?php _e( 'Maintenance and Security Releases' ); ?></h3>
+			<p>
+				<?php
+				printf(
+					/* translators: %s: WordPress version number */
+					__( '<strong>Version %s</strong> addressed some security issues.' ),
+					'5.1.16'
+				);
+				?>
+				<?php
+				printf(
+					/* translators: %s: HelpHub URL */
+					__( 'For more information, see <a href="%s">the release notes</a>.' ),
+					sprintf(
+						/* translators: %s: WordPress version */
+						esc_url( __( 'https://wordpress.org/support/wordpress-version/version-%s/' ) ),
+						sanitize_title( '5.1.16' )
+					)
+				);
+				?>
+			</p>
 			<p>
 				<?php
 				printf(
diff --git a/wp-admin/includes/ajax-actions.php b/wp-admin/includes/ajax-actions.php
index 49534609bf..3d0014bd8a 100644
--- a/wp-admin/includes/ajax-actions.php
+++ b/wp-admin/includes/ajax-actions.php
@@ -2507,6 +2507,10 @@ function wp_ajax_set_attachment_thumbnail() {
 		wp_send_json_error();
 	}
 
+	if ( false === check_ajax_referer( 'set-attachment-thumbnail', '_ajax_nonce', false ) ) {
+		wp_send_json_error();
+	}
+
 	$post_ids = array();
 	// For each URL, try to find its corresponding post ID.
 	foreach ( $_POST['urls'] as $url ) {
diff --git a/wp-includes/blocks.php b/wp-includes/blocks.php
index 1ee3536f69..eac353b5db 100644
--- a/wp-includes/blocks.php
+++ b/wp-includes/blocks.php
@@ -271,6 +271,10 @@ function serialize_blocks( $blocks ) {
 function filter_block_content( $text, $allowed_html = 'post', $allowed_protocols = array() ) {
 	$result = '';
 
+	if ( false !== strpos( $text, '<!--' ) && false !== strpos( $text, '--->' ) ) {
+		$text = preg_replace_callback( '%<!--(.*?)--->%', '_filter_block_content_callback', $text );
+	}
+
 	$blocks = parse_blocks( $text );
 	foreach ( $blocks as $block ) {
 		$block   = filter_block_kses( $block, $allowed_html, $allowed_protocols );
@@ -280,6 +284,19 @@ function filter_block_content( $text, $allowed_html = 'post', $allowed_protocols
 	return $result;
 }
 
+/**
+ * Callback used for regular expression replacement in filter_block_content().
+ *
+ * @private
+ * @since 6.2.1
+ *
+ * @param array $matches Array of preg_replace_callback matches.
+ * @return string Replacement string.
+ */
+function _filter_block_content_callback( $matches ) {
+	return '<!--' . rtrim( $matches[1], '-' ) . '-->';
+}
+
 /**
  * Filters and sanitizes a parsed block to remove non-allowable HTML from block
  * attribute values.
diff --git a/wp-includes/embed.php b/wp-includes/embed.php
index bf6a5402cb..f6e58f47b5 100644
--- a/wp-includes/embed.php
+++ b/wp-includes/embed.php
@@ -455,7 +455,7 @@ function get_post_embed_html( $width, $height, $post = null ) {
 		 * and edit wp-embed.js directly.
 		 */
 		$output .= <<<JS
-		!function(c,d){"use strict";var e=!1,n=!1;if(d.querySelector)if(c.addEventListener)e=!0;if(c.wp=c.wp||{},!c.wp.receiveEmbedMessage)if(c.wp.receiveEmbedMessage=function(e){var t=e.data;if(t)if(t.secret||t.message||t.value)if(!/[^a-zA-Z0-9]/.test(t.secret)){for(var r,a,i,s=d.querySelectorAll('iframe[data-secret="'+t.secret+'"]'),n=d.querySelectorAll('blockquote[data-secret="'+t.secret+'"]'),o=0;o<n.length;o++)n[o].style.display="none";for(o=0;o<s.length;o++)if(r=s[o],e.source===r.contentWindow){if(r.removeAttribute("style"),"height"===t.message){if(1e3<(i=parseInt(t.value,10)))i=1e3;else if(~~i<200)i=200;r.height=i}if("link"===t.message)if(a=d.createElement("a"),i=d.createElement("a"),a.href=r.getAttribute("src"),i.href=t.value,i.host===a.host)if(d.activeElement===r)c.top.location.href=t.value}}},e)c.addEventListener("message",c.wp.receiveEmbedMessage,!1),d.addEventListener("DOMContentLoaded",t,!1),c.addEventListener("load",t,!1);function t(){if(!n){n=!0;for(var e,t,r=-1!==navigator.appVersion.indexOf("MSIE 10"),a=!!navigator.userAgent.match(/Trident.*rv:11\./),i=d.querySelectorAll("iframe.wp-embedded-content"),s=0;s<i.length;s++){if(!(e=i[s]).getAttribute("data-secret"))t=Math.random().toString(36).substr(2,10),e.src+="#?secret="+t,e.setAttribute("data-secret",t);if(r||a)(t=e.cloneNode(!0)).removeAttribute("security"),e.parentNode.replaceChild(t,e)}}}}(window,document);
+		!function(d,l){"use strict";var e=!1,n=!1;if(l.querySelector)if(d.addEventListener)e=!0;if(d.wp=d.wp||{},!d.wp.receiveEmbedMessage)if(d.wp.receiveEmbedMessage=function(e){var t=e.data;if(t)if(t.secret||t.message||t.value)if(!/[^a-zA-Z0-9]/.test(t.secret)){for(var r,i,a,s=l.querySelectorAll('iframe[data-secret="'+t.secret+'"]'),n=l.querySelectorAll('blockquote[data-secret="'+t.secret+'"]'),o=new RegExp("^https?:$","i"),c=0;c<n.length;c++)n[c].style.display="none";for(c=0;c<s.length;c++)if(r=s[c],e.source===r.contentWindow){if(r.removeAttribute("style"),"height"===t.message){if(1e3<(a=parseInt(t.value,10)))a=1e3;else if(~~a<200)a=200;r.height=a}if("link"===t.message)if(i=l.createElement("a"),a=l.createElement("a"),i.href=r.getAttribute("src"),a.href=t.value,o.test(a.protocol))if(a.host===i.host)if(l.activeElement===r)d.top.location.href=t.value}}},e)d.addEventListener("message",d.wp.receiveEmbedMessage,!1),l.addEventListener("DOMContentLoaded",t,!1),d.addEventListener("load",t,!1);function t(){if(!n){n=!0;for(var e,t,r=-1!==navigator.appVersion.indexOf("MSIE 10"),i=!!navigator.userAgent.match(/Trident.*rv:11\./),a=l.querySelectorAll("iframe.wp-embedded-content"),s=0;s<a.length;s++){if(!(e=a[s]).getAttribute("data-secret"))t=Math.random().toString(36).substr(2,10),e.src+="#?secret="+t,e.setAttribute("data-secret",t);if(r||i)(t=e.cloneNode(!0)).removeAttribute("security"),e.parentNode.replaceChild(t,e)}}}}(window,document);
 JS;
 	}
 	$output .= "\n//--><!]]>";
diff --git a/wp-includes/formatting.php b/wp-includes/formatting.php
index 80dab5dcf5..76f9008a21 100644
--- a/wp-includes/formatting.php
+++ b/wp-includes/formatting.php
@@ -2365,6 +2365,29 @@ function sanitize_html_class( $class, $fallback = '' ) {
 	return apply_filters( 'sanitize_html_class', $sanitized, $class, $fallback );
 }
 
+/**
+ * Strips out all characters not allowed in a locale name.
+ *
+ * @since 6.2.1
+ *
+ * @param string $locale_name The locale name to be sanitized.
+ * @return string The sanitized value.
+ */
+function sanitize_locale_name( $locale_name ) {
+	// Limit to A-Z, a-z, 0-9, '_', '-'.
+	$sanitized = preg_replace( '/[^A-Za-z0-9_-]/', '', $locale_name );
+
+	/**
+	 * Filters a sanitized locale name string.
+	 *
+	 * @since 6.2.1
+	 *
+	 * @param string $sanitized   The sanitized locale name.
+	 * @param string $locale_name The locale name before sanitization.
+	 */
+	return apply_filters( 'sanitize_locale_name', $sanitized, $locale_name );
+}
+
 /**
  * Converts lone & characters into `&#038;` (a.k.a. `&amp;`)
  *
diff --git a/wp-includes/js/media-audiovideo.js b/wp-includes/js/media-audiovideo.js
index ee5d7f92de..bbc2bc8bbb 100644
--- a/wp-includes/js/media-audiovideo.js
+++ b/wp-includes/js/media-audiovideo.js
@@ -837,6 +837,7 @@ VideoDetails = MediaDetails.extend(/** @lends wp.media.view.MediaFrame.VideoDeta
 
 			wp.ajax.send( 'set-attachment-thumbnail', {
 				data : {
+					_ajax_nonce: wp.media.view.settings.nonce.setAttachmentThumbnail,
 					urls: urls,
 					thumbnail_id: attachment.get( 'id' )
 				}
diff --git a/wp-includes/js/media-audiovideo.min.js b/wp-includes/js/media-audiovideo.min.js
index 0089c4eb23..3a5bb93695 100644
--- a/wp-includes/js/media-audiovideo.min.js
+++ b/wp-includes/js/media-audiovideo.min.js
@@ -1 +1 @@
-!function(i){var a={};function o(e){if(a[e])return a[e].exports;var t=a[e]={i:e,l:!1,exports:{}};return i[e].call(t.exports,t,t.exports,o),t.l=!0,t.exports}o.m=i,o.c=a,o.d=function(e,t,i){o.o(e,t)||Object.defineProperty(e,t,{enumerable:!0,get:i})},o.r=function(e){"undefined"!=typeof Symbol&&Symbol.toStringTag&&Object.defineProperty(e,Symbol.toStringTag,{value:"Module"}),Object.defineProperty(e,"__esModule",{value:!0})},o.t=function(t,e){if(1&e&&(t=o(t)),8&e)return t;if(4&e&&"object"==typeof t&&t&&t.__esModule)return t;var i=Object.create(null);if(o.r(i),Object.defineProperty(i,"default",{enumerable:!0,value:t}),2&e&&"string"!=typeof t)for(var a in t)o.d(i,a,function(e){return t[e]}.bind(null,a));return i},o.n=function(e){var t=e&&e.__esModule?function(){return e.default}:function(){return e};return o.d(t,"a",t),t},o.o=function(e,t){return Object.prototype.hasOwnProperty.call(e,t)},o.p="",o(o.s=0)}([function(e,t,i){e.exports=i(1)},function(e,t,i){var a=wp.media,o=window._wpmejsSettings||{},n=window._wpMediaViewsL10n||{};wp.media.mixin={mejsSettings:o,removeAllPlayers:function(){if(window.mejs&&window.mejs.players)for(var e in window.mejs.players)window.mejs.players[e].pause(),this.removePlayer(window.mejs.players[e])},removePlayer:function(e){var t,i;if(e.options){for(t in e.options.features)if(e["clean"+(i=e.options.features[t])])try{e["clean"+i](e)}catch(e){}e.isDynamic||e.node.remove(),"html5"!==e.media.rendererName&&e.media.remove(),delete window.mejs.players[e.id],e.container.remove(),e.globalUnbind("resize",e.globalResizeCallback),e.globalUnbind("keydown",e.globalKeydownCallback),e.globalUnbind("click",e.globalClickCallback),delete e.media.player}},unsetPlayers:function(){this.players&&this.players.length&&(_.each(this.players,function(e){e.pause(),wp.media.mixin.removePlayer(e)}),this.players=[])}},wp.media.playlist=new wp.media.collection({tag:"playlist",editTitle:n.editPlaylistTitle,defaults:{id:wp.media.view.settings.post.id,style:"light",tracklist:!0,tracknumbers:!0,images:!0,artists:!0,type:"audio"}}),wp.media.audio={coerce:wp.media.coerce,defaults:{id:wp.media.view.settings.post.id,src:"",loop:!1,autoplay:!1,preload:"none",width:400},edit:function(e){e=wp.shortcode.next("audio",e).shortcode;return wp.media({frame:"audio",state:"audio-details",metadata:_.defaults(e.attrs.named,this.defaults)})},shortcode:function(i){var e;return _.each(this.defaults,function(e,t){i[t]=this.coerce(i,t),e===i[t]&&delete i[t]},this),e=i.content,delete i.content,new wp.shortcode({tag:"audio",attrs:i,content:e})}},wp.media.video={coerce:wp.media.coerce,defaults:{id:wp.media.view.settings.post.id,src:"",poster:"",loop:!1,autoplay:!1,preload:"metadata",content:"",width:640,height:360},edit:function(e){var t=wp.shortcode.next("video",e).shortcode,e=t.attrs.named;return e.content=t.content,wp.media({frame:"video",state:"video-details",metadata:_.defaults(e,this.defaults)})},shortcode:function(i){var e;return _.each(this.defaults,function(e,t){i[t]=this.coerce(i,t),e===i[t]&&delete i[t]},this),e=i.content,delete i.content,new wp.shortcode({tag:"video",attrs:i,content:e})}},a.model.PostMedia=i(2),a.controller.AudioDetails=i(3),a.controller.VideoDetails=i(4),a.view.MediaFrame.MediaDetails=i(5),a.view.MediaFrame.AudioDetails=i(6),a.view.MediaFrame.VideoDetails=i(7),a.view.MediaDetails=i(8),a.view.AudioDetails=i(9),a.view.VideoDetails=i(10)},function(e,t){var i=Backbone.Model.extend({initialize:function(){this.attachment=!1},setSource:function(e){this.attachment=e,this.extension=e.get("filename").split(".").pop(),this.get("src")&&this.extension===this.get("src").split(".").pop()&&this.unset("src"),_.contains(wp.media.view.settings.embedExts,this.extension)?this.set(this.extension,this.attachment.get("url")):this.unset(this.extension)},changeAttachment:function(e){this.setSource(e),this.unset("src"),_.each(_.without(wp.media.view.settings.embedExts,this.extension),function(e){this.unset(e)},this)}});e.exports=i},function(e,t){var i=wp.media.controller.State,a=wp.media.view.l10n,a=i.extend({defaults:{id:"audio-details",toolbar:"audio-details",title:a.audioDetailsTitle,content:"audio-details",menu:"audio-details",router:!1,priority:60},initialize:function(e){this.media=e.media,i.prototype.initialize.apply(this,arguments)}});e.exports=a},function(e,t){var i=wp.media.controller.State,a=wp.media.view.l10n,a=i.extend({defaults:{id:"video-details",toolbar:"video-details",title:a.videoDetailsTitle,content:"video-details",menu:"video-details",router:!1,priority:60},initialize:function(e){this.media=e.media,i.prototype.initialize.apply(this,arguments)}});e.exports=a},function(e,t){var i=wp.media.view.MediaFrame.Select,a=wp.media.view.l10n,o=i.extend({defaults:{id:"media",url:"",menu:"media-details",content:"media-details",toolbar:"media-details",type:"link",priority:120},initialize:function(e){this.DetailsView=e.DetailsView,this.cancelText=e.cancelText,this.addText=e.addText,this.media=new wp.media.model.PostMedia(e.metadata),this.options.selection=new wp.media.model.Selection(this.media.attachment,{multiple:!1}),i.prototype.initialize.apply(this,arguments)},bindHandlers:function(){var e=this.defaults.menu;i.prototype.bindHandlers.apply(this,arguments),this.on("menu:create:"+e,this.createMenu,this),this.on("content:render:"+e,this.renderDetailsContent,this),this.on("menu:render:"+e,this.renderMenu,this),this.on("toolbar:render:"+e,this.renderDetailsToolbar,this)},renderDetailsContent:function(){var e=new this.DetailsView({controller:this,model:this.state().media,attachment:this.state().media.attachment}).render();this.content.set(e)},renderMenu:function(e){var t=this.lastState(),i=t&&t.id,a=this;e.set({cancel:{text:this.cancelText,priority:20,click:function(){i?a.setState(i):a.close()}},separateCancel:new wp.media.View({className:"separator",priority:40})})},setPrimaryButton:function(e,t){this.toolbar.set(new wp.media.view.Toolbar({controller:this,items:{button:{style:"primary",text:e,priority:80,click:function(){var e=this.controller;t.call(this,e,e.state()),e.setState(e.options.state),e.reset()}}}}))},renderDetailsToolbar:function(){this.setPrimaryButton(a.update,function(e,t){e.close(),t.trigger("update",e.media.toJSON())})},renderReplaceToolbar:function(){this.setPrimaryButton(a.replace,function(e,t){var i=t.get("selection").single();e.media.changeAttachment(i),t.trigger("replace",e.media.toJSON())})},renderAddSourceToolbar:function(){this.setPrimaryButton(this.addText,function(e,t){var i=t.get("selection").single();e.media.setSource(i),t.trigger("add-source",e.media.toJSON())})}});e.exports=o},function(e,t){var i=wp.media.view.MediaFrame.MediaDetails,a=wp.media.controller.MediaLibrary,o=wp.media.view.l10n,n=i.extend({defaults:{id:"audio",url:"",menu:"audio-details",content:"audio-details",toolbar:"audio-details",type:"link",title:o.audioDetailsTitle,priority:120},initialize:function(e){e.DetailsView=wp.media.view.AudioDetails,e.cancelText=o.audioDetailsCancel,e.addText=o.audioAddSourceTitle,i.prototype.initialize.call(this,e)},bindHandlers:function(){i.prototype.bindHandlers.apply(this,arguments),this.on("toolbar:render:replace-audio",this.renderReplaceToolbar,this),this.on("toolbar:render:add-audio-source",this.renderAddSourceToolbar,this)},createStates:function(){this.states.add([new wp.media.controller.AudioDetails({media:this.media}),new a({type:"audio",id:"replace-audio",title:o.audioReplaceTitle,toolbar:"replace-audio",media:this.media,menu:"audio-details"}),new a({type:"audio",id:"add-audio-source",title:o.audioAddSourceTitle,toolbar:"add-audio-source",media:this.media,menu:!1})])}});e.exports=n},function(e,t){var i=wp.media.view.MediaFrame.MediaDetails,a=wp.media.controller.MediaLibrary,o=wp.media.view.l10n,n=i.extend({defaults:{id:"video",url:"",menu:"video-details",content:"video-details",toolbar:"video-details",type:"link",title:o.videoDetailsTitle,priority:120},initialize:function(e){e.DetailsView=wp.media.view.VideoDetails,e.cancelText=o.videoDetailsCancel,e.addText=o.videoAddSourceTitle,i.prototype.initialize.call(this,e)},bindHandlers:function(){i.prototype.bindHandlers.apply(this,arguments),this.on("toolbar:render:replace-video",this.renderReplaceToolbar,this),this.on("toolbar:render:add-video-source",this.renderAddSourceToolbar,this),this.on("toolbar:render:select-poster-image",this.renderSelectPosterImageToolbar,this),this.on("toolbar:render:add-track",this.renderAddTrackToolbar,this)},createStates:function(){this.states.add([new wp.media.controller.VideoDetails({media:this.media}),new a({type:"video",id:"replace-video",title:o.videoReplaceTitle,toolbar:"replace-video",media:this.media,menu:"video-details"}),new a({type:"video",id:"add-video-source",title:o.videoAddSourceTitle,toolbar:"add-video-source",media:this.media,menu:!1}),new a({type:"image",id:"select-poster-image",title:o.videoSelectPosterImageTitle,toolbar:"select-poster-image",media:this.media,menu:"video-details"}),new a({type:"text",id:"add-track",title:o.videoAddTrackTitle,toolbar:"add-track",media:this.media,menu:"video-details"})])},renderSelectPosterImageToolbar:function(){this.setPrimaryButton(o.videoSelectPosterImageTitle,function(t,e){var i=[],a=e.get("selection").single();t.media.set("poster",a.get("url")),e.trigger("set-poster-image",t.media.toJSON()),_.each(wp.media.view.settings.embedExts,function(e){t.media.get(e)&&i.push(t.media.get(e))}),wp.ajax.send("set-attachment-thumbnail",{data:{urls:i,thumbnail_id:a.get("id")}})})},renderAddTrackToolbar:function(){this.setPrimaryButton(o.videoAddTrackTitle,function(e,t){var i=t.get("selection").single(),a=e.media.get("content");-1===a.indexOf(i.get("url"))&&(a+=['<track srclang="en" label="English" kind="subtitles" src="',i.get("url"),'" />'].join(""),e.media.set("content",a)),t.trigger("add-track",e.media.toJSON())})}});e.exports=n},function(e,t){var i=wp.media.view.Settings.AttachmentDisplay,a=jQuery,o=i.extend({initialize:function(){_.bindAll(this,"success"),this.players=[],this.listenTo(this.controller,"close",wp.media.mixin.unsetPlayers),this.on("ready",this.setPlayer),this.on("media:setting:remove",wp.media.mixin.unsetPlayers,this),this.on("media:setting:remove",this.render),this.on("media:setting:remove",this.setPlayer),i.prototype.initialize.apply(this,arguments)},events:function(){return _.extend({"click .remove-setting":"removeSetting","change .content-track":"setTracks","click .remove-track":"setTracks","click .add-media-source":"addSource"},i.prototype.events)},prepare:function(){return _.defaults({model:this.model.toJSON()},this.options)},removeSetting:function(e){var t=a(e.currentTarget).parent(),e=t.find("input").data("setting");e&&(this.model.unset(e),this.trigger("media:setting:remove",this)),t.remove()},setTracks:function(){var t="";_.each(this.$(".content-track"),function(e){t+=a(e).val()}),this.model.set("content",t),this.trigger("media:setting:remove",this)},addSource:function(e){this.controller.lastMime=a(e.currentTarget).data("mime"),this.controller.setState("add-"+this.controller.defaults.id+"-source")},loadPlayer:function(){this.players.push(new MediaElementPlayer(this.media,this.settings)),this.scriptXhr=!1},setPlayer:function(){var e;this.players.length||!this.media||this.scriptXhr||((e=this.model.get("src"))&&-1<e.indexOf("vimeo")&&!("Vimeo"in window)?this.scriptXhr=a.getScript("https://player.vimeo.com/api/player.js",_.bind(this.loadPlayer,this)):this.loadPlayer())},setMedia:function(){return this},success:function(e){var t=e.attributes.autoplay&&"false"!==e.attributes.autoplay;"flash"===e.pluginType&&t&&e.addEventListener("canplay",function(){e.play()},!1),this.mejs=e},render:function(){return i.prototype.render.apply(this,arguments),setTimeout(_.bind(function(){this.resetFocus()},this),10),this.settings=_.defaults({success:this.success},wp.media.mixin.mejsSettings),this.setMedia()},resetFocus:function(){this.$(".embed-media-settings").scrollTop(0)}},{instances:0,prepareSrc:function(e){var t=o.instances++;return _.each(a(e).find("source"),function(e){e.src=[e.src,-1<e.src.indexOf("?")?"&":"?","_=",t].join("")}),e}});e.exports=o},function(e,t){var i=wp.media.view.MediaDetails,a=i.extend({className:"audio-details",template:wp.template("audio-details"),setMedia:function(){var e=this.$(".wp-audio-shortcode");return e.find("source").length?(e.is(":hidden")&&e.show(),this.media=i.prepareSrc(e.get(0))):(e.hide(),this.media=!1),this}});e.exports=a},function(e,t){var i=wp.media.view.MediaDetails,a=i.extend({className:"video-details",template:wp.template("video-details"),setMedia:function(){var e=this.$(".wp-video-shortcode");return e.find("source").length?(e.is(":hidden")&&e.show(),e.hasClass("youtube-video")||e.hasClass("vimeo-video")?this.media=e.get(0):this.media=i.prepareSrc(e.get(0))):(e.hide(),this.media=!1),this}});e.exports=a}]);
\ No newline at end of file
+!function(i){var a={};function n(e){if(a[e])return a[e].exports;var t=a[e]={i:e,l:!1,exports:{}};return i[e].call(t.exports,t,t.exports,n),t.l=!0,t.exports}n.m=i,n.c=a,n.d=function(e,t,i){n.o(e,t)||Object.defineProperty(e,t,{enumerable:!0,get:i})},n.r=function(e){"undefined"!=typeof Symbol&&Symbol.toStringTag&&Object.defineProperty(e,Symbol.toStringTag,{value:"Module"}),Object.defineProperty(e,"__esModule",{value:!0})},n.t=function(t,e){if(1&e&&(t=n(t)),8&e)return t;if(4&e&&"object"==typeof t&&t&&t.__esModule)return t;var i=Object.create(null);if(n.r(i),Object.defineProperty(i,"default",{enumerable:!0,value:t}),2&e&&"string"!=typeof t)for(var a in t)n.d(i,a,function(e){return t[e]}.bind(null,a));return i},n.n=function(e){var t=e&&e.__esModule?function(){return e.default}:function(){return e};return n.d(t,"a",t),t},n.o=function(e,t){return Object.prototype.hasOwnProperty.call(e,t)},n.p="",n(n.s=0)}([function(e,t,i){e.exports=i(1)},function(e,t,i){var a=wp.media,n=window._wpmejsSettings||{},o=window._wpMediaViewsL10n||{};wp.media.mixin={mejsSettings:n,removeAllPlayers:function(){if(window.mejs&&window.mejs.players)for(var e in window.mejs.players)window.mejs.players[e].pause(),this.removePlayer(window.mejs.players[e])},removePlayer:function(e){var t,i;if(e.options){for(t in e.options.features)if(e["clean"+(i=e.options.features[t])])try{e["clean"+i](e)}catch(e){}e.isDynamic||e.node.remove(),"html5"!==e.media.rendererName&&e.media.remove(),delete window.mejs.players[e.id],e.container.remove(),e.globalUnbind("resize",e.globalResizeCallback),e.globalUnbind("keydown",e.globalKeydownCallback),e.globalUnbind("click",e.globalClickCallback),delete e.media.player}},unsetPlayers:function(){this.players&&this.players.length&&(_.each(this.players,function(e){e.pause(),wp.media.mixin.removePlayer(e)}),this.players=[])}},wp.media.playlist=new wp.media.collection({tag:"playlist",editTitle:o.editPlaylistTitle,defaults:{id:wp.media.view.settings.post.id,style:"light",tracklist:!0,tracknumbers:!0,images:!0,artists:!0,type:"audio"}}),wp.media.audio={coerce:wp.media.coerce,defaults:{id:wp.media.view.settings.post.id,src:"",loop:!1,autoplay:!1,preload:"none",width:400},edit:function(e){e=wp.shortcode.next("audio",e).shortcode;return wp.media({frame:"audio",state:"audio-details",metadata:_.defaults(e.attrs.named,this.defaults)})},shortcode:function(i){var e;return _.each(this.defaults,function(e,t){i[t]=this.coerce(i,t),e===i[t]&&delete i[t]},this),e=i.content,delete i.content,new wp.shortcode({tag:"audio",attrs:i,content:e})}},wp.media.video={coerce:wp.media.coerce,defaults:{id:wp.media.view.settings.post.id,src:"",poster:"",loop:!1,autoplay:!1,preload:"metadata",content:"",width:640,height:360},edit:function(e){var t=wp.shortcode.next("video",e).shortcode,e=t.attrs.named;return e.content=t.content,wp.media({frame:"video",state:"video-details",metadata:_.defaults(e,this.defaults)})},shortcode:function(i){var e;return _.each(this.defaults,function(e,t){i[t]=this.coerce(i,t),e===i[t]&&delete i[t]},this),e=i.content,delete i.content,new wp.shortcode({tag:"video",attrs:i,content:e})}},a.model.PostMedia=i(2),a.controller.AudioDetails=i(3),a.controller.VideoDetails=i(4),a.view.MediaFrame.MediaDetails=i(5),a.view.MediaFrame.AudioDetails=i(6),a.view.MediaFrame.VideoDetails=i(7),a.view.MediaDetails=i(8),a.view.AudioDetails=i(9),a.view.VideoDetails=i(10)},function(e,t){var i=Backbone.Model.extend({initialize:function(){this.attachment=!1},setSource:function(e){this.attachment=e,this.extension=e.get("filename").split(".").pop(),this.get("src")&&this.extension===this.get("src").split(".").pop()&&this.unset("src"),_.contains(wp.media.view.settings.embedExts,this.extension)?this.set(this.extension,this.attachment.get("url")):this.unset(this.extension)},changeAttachment:function(e){this.setSource(e),this.unset("src"),_.each(_.without(wp.media.view.settings.embedExts,this.extension),function(e){this.unset(e)},this)}});e.exports=i},function(e,t){var i=wp.media.controller.State,a=wp.media.view.l10n,a=i.extend({defaults:{id:"audio-details",toolbar:"audio-details",title:a.audioDetailsTitle,content:"audio-details",menu:"audio-details",router:!1,priority:60},initialize:function(e){this.media=e.media,i.prototype.initialize.apply(this,arguments)}});e.exports=a},function(e,t){var i=wp.media.controller.State,a=wp.media.view.l10n,a=i.extend({defaults:{id:"video-details",toolbar:"video-details",title:a.videoDetailsTitle,content:"video-details",menu:"video-details",router:!1,priority:60},initialize:function(e){this.media=e.media,i.prototype.initialize.apply(this,arguments)}});e.exports=a},function(e,t){var i=wp.media.view.MediaFrame.Select,a=wp.media.view.l10n,n=i.extend({defaults:{id:"media",url:"",menu:"media-details",content:"media-details",toolbar:"media-details",type:"link",priority:120},initialize:function(e){this.DetailsView=e.DetailsView,this.cancelText=e.cancelText,this.addText=e.addText,this.media=new wp.media.model.PostMedia(e.metadata),this.options.selection=new wp.media.model.Selection(this.media.attachment,{multiple:!1}),i.prototype.initialize.apply(this,arguments)},bindHandlers:function(){var e=this.defaults.menu;i.prototype.bindHandlers.apply(this,arguments),this.on("menu:create:"+e,this.createMenu,this),this.on("content:render:"+e,this.renderDetailsContent,this),this.on("menu:render:"+e,this.renderMenu,this),this.on("toolbar:render:"+e,this.renderDetailsToolbar,this)},renderDetailsContent:function(){var e=new this.DetailsView({controller:this,model:this.state().media,attachment:this.state().media.attachment}).render();this.content.set(e)},renderMenu:function(e){var t=this.lastState(),i=t&&t.id,a=this;e.set({cancel:{text:this.cancelText,priority:20,click:function(){i?a.setState(i):a.close()}},separateCancel:new wp.media.View({className:"separator",priority:40})})},setPrimaryButton:function(e,t){this.toolbar.set(new wp.media.view.Toolbar({controller:this,items:{button:{style:"primary",text:e,priority:80,click:function(){var e=this.controller;t.call(this,e,e.state()),e.setState(e.options.state),e.reset()}}}}))},renderDetailsToolbar:function(){this.setPrimaryButton(a.update,function(e,t){e.close(),t.trigger("update",e.media.toJSON())})},renderReplaceToolbar:function(){this.setPrimaryButton(a.replace,function(e,t){var i=t.get("selection").single();e.media.changeAttachment(i),t.trigger("replace",e.media.toJSON())})},renderAddSourceToolbar:function(){this.setPrimaryButton(this.addText,function(e,t){var i=t.get("selection").single();e.media.setSource(i),t.trigger("add-source",e.media.toJSON())})}});e.exports=n},function(e,t){var i=wp.media.view.MediaFrame.MediaDetails,a=wp.media.controller.MediaLibrary,n=wp.media.view.l10n,o=i.extend({defaults:{id:"audio",url:"",menu:"audio-details",content:"audio-details",toolbar:"audio-details",type:"link",title:n.audioDetailsTitle,priority:120},initialize:function(e){e.DetailsView=wp.media.view.AudioDetails,e.cancelText=n.audioDetailsCancel,e.addText=n.audioAddSourceTitle,i.prototype.initialize.call(this,e)},bindHandlers:function(){i.prototype.bindHandlers.apply(this,arguments),this.on("toolbar:render:replace-audio",this.renderReplaceToolbar,this),this.on("toolbar:render:add-audio-source",this.renderAddSourceToolbar,this)},createStates:function(){this.states.add([new wp.media.controller.AudioDetails({media:this.media}),new a({type:"audio",id:"replace-audio",title:n.audioReplaceTitle,toolbar:"replace-audio",media:this.media,menu:"audio-details"}),new a({type:"audio",id:"add-audio-source",title:n.audioAddSourceTitle,toolbar:"add-audio-source",media:this.media,menu:!1})])}});e.exports=o},function(e,t){var i=wp.media.view.MediaFrame.MediaDetails,a=wp.media.controller.MediaLibrary,n=wp.media.view.l10n,o=i.extend({defaults:{id:"video",url:"",menu:"video-details",content:"video-details",toolbar:"video-details",type:"link",title:n.videoDetailsTitle,priority:120},initialize:function(e){e.DetailsView=wp.media.view.VideoDetails,e.cancelText=n.videoDetailsCancel,e.addText=n.videoAddSourceTitle,i.prototype.initialize.call(this,e)},bindHandlers:function(){i.prototype.bindHandlers.apply(this,arguments),this.on("toolbar:render:replace-video",this.renderReplaceToolbar,this),this.on("toolbar:render:add-video-source",this.renderAddSourceToolbar,this),this.on("toolbar:render:select-poster-image",this.renderSelectPosterImageToolbar,this),this.on("toolbar:render:add-track",this.renderAddTrackToolbar,this)},createStates:function(){this.states.add([new wp.media.controller.VideoDetails({media:this.media}),new a({type:"video",id:"replace-video",title:n.videoReplaceTitle,toolbar:"replace-video",media:this.media,menu:"video-details"}),new a({type:"video",id:"add-video-source",title:n.videoAddSourceTitle,toolbar:"add-video-source",media:this.media,menu:!1}),new a({type:"image",id:"select-poster-image",title:n.videoSelectPosterImageTitle,toolbar:"select-poster-image",media:this.media,menu:"video-details"}),new a({type:"text",id:"add-track",title:n.videoAddTrackTitle,toolbar:"add-track",media:this.media,menu:"video-details"})])},renderSelectPosterImageToolbar:function(){this.setPrimaryButton(n.videoSelectPosterImageTitle,function(t,e){var i=[],a=e.get("selection").single();t.media.set("poster",a.get("url")),e.trigger("set-poster-image",t.media.toJSON()),_.each(wp.media.view.settings.embedExts,function(e){t.media.get(e)&&i.push(t.media.get(e))}),wp.ajax.send("set-attachment-thumbnail",{data:{_ajax_nonce:wp.media.view.settings.nonce.setAttachmentThumbnail,urls:i,thumbnail_id:a.get("id")}})})},renderAddTrackToolbar:function(){this.setPrimaryButton(n.videoAddTrackTitle,function(e,t){var i=t.get("selection").single(),a=e.media.get("content");-1===a.indexOf(i.get("url"))&&(a+=['<track srclang="en" label="English" kind="subtitles" src="',i.get("url"),'" />'].join(""),e.media.set("content",a)),t.trigger("add-track",e.media.toJSON())})}});e.exports=o},function(e,t){var i=wp.media.view.Settings.AttachmentDisplay,a=jQuery,n=i.extend({initialize:function(){_.bindAll(this,"success"),this.players=[],this.listenTo(this.controller,"close",wp.media.mixin.unsetPlayers),this.on("ready",this.setPlayer),this.on("media:setting:remove",wp.media.mixin.unsetPlayers,this),this.on("media:setting:remove",this.render),this.on("media:setting:remove",this.setPlayer),i.prototype.initialize.apply(this,arguments)},events:function(){return _.extend({"click .remove-setting":"removeSetting","change .content-track":"setTracks","click .remove-track":"setTracks","click .add-media-source":"addSource"},i.prototype.events)},prepare:function(){return _.defaults({model:this.model.toJSON()},this.options)},removeSetting:function(e){var t=a(e.currentTarget).parent(),e=t.find("input").data("setting");e&&(this.model.unset(e),this.trigger("media:setting:remove",this)),t.remove()},setTracks:function(){var t="";_.each(this.$(".content-track"),function(e){t+=a(e).val()}),this.model.set("content",t),this.trigger("media:setting:remove",this)},addSource:function(e){this.controller.lastMime=a(e.currentTarget).data("mime"),this.controller.setState("add-"+this.controller.defaults.id+"-source")},loadPlayer:function(){this.players.push(new MediaElementPlayer(this.media,this.settings)),this.scriptXhr=!1},setPlayer:function(){var e;this.players.length||!this.media||this.scriptXhr||((e=this.model.get("src"))&&-1<e.indexOf("vimeo")&&!("Vimeo"in window)?this.scriptXhr=a.getScript("https://player.vimeo.com/api/player.js",_.bind(this.loadPlayer,this)):this.loadPlayer())},setMedia:function(){return this},success:function(e){var t=e.attributes.autoplay&&"false"!==e.attributes.autoplay;"flash"===e.pluginType&&t&&e.addEventListener("canplay",function(){e.play()},!1),this.mejs=e},render:function(){return i.prototype.render.apply(this,arguments),setTimeout(_.bind(function(){this.resetFocus()},this),10),this.settings=_.defaults({success:this.success},wp.media.mixin.mejsSettings),this.setMedia()},resetFocus:function(){this.$(".embed-media-settings").scrollTop(0)}},{instances:0,prepareSrc:function(e){var t=n.instances++;return _.each(a(e).find("source"),function(e){e.src=[e.src,-1<e.src.indexOf("?")?"&":"?","_=",t].join("")}),e}});e.exports=n},function(e,t){var i=wp.media.view.MediaDetails,a=i.extend({className:"audio-details",template:wp.template("audio-details"),setMedia:function(){var e=this.$(".wp-audio-shortcode");return e.find("source").length?(e.is(":hidden")&&e.show(),this.media=i.prepareSrc(e.get(0))):(e.hide(),this.media=!1),this}});e.exports=a},function(e,t){var i=wp.media.view.MediaDetails,a=i.extend({className:"video-details",template:wp.template("video-details"),setMedia:function(){var e=this.$(".wp-video-shortcode");return e.find("source").length?(e.is(":hidden")&&e.show(),e.hasClass("youtube-video")||e.hasClass("vimeo-video")?this.media=e.get(0):this.media=i.prepareSrc(e.get(0))):(e.hide(),this.media=!1),this}});e.exports=a}]);
\ No newline at end of file
diff --git a/wp-includes/js/wp-embed.js b/wp-includes/js/wp-embed.js
index 887c7483fb..63c59f2fb0 100644
--- a/wp-includes/js/wp-embed.js
+++ b/wp-includes/js/wp-embed.js
@@ -44,6 +44,7 @@
 
 		var iframes = document.querySelectorAll( 'iframe[data-secret="' + data.secret + '"]' ),
 			blockquotes = document.querySelectorAll( 'blockquote[data-secret="' + data.secret + '"]' ),
+			allowedProtocols = new RegExp( '^https?:$', 'i' ),
 			i, source, height, sourceURL, targetURL;
 
 		for ( i = 0; i < blockquotes.length; i++ ) {
@@ -79,6 +80,11 @@
 				sourceURL.href = source.getAttribute( 'src' );
 				targetURL.href = data.value;
 
+				/* Only follow link if the protocol is in the allow list. */
+				if ( ! allowedProtocols.test( targetURL.protocol ) ) {
+					continue;
+				}
+
 				/* Only continue if link hostname matches iframe's hostname. */
 				if ( targetURL.host === sourceURL.host ) {
 					if ( document.activeElement === source ) {
diff --git a/wp-includes/js/wp-embed.min.js b/wp-includes/js/wp-embed.min.js
index 4860629324..f4a49c5493 100644
--- a/wp-includes/js/wp-embed.min.js
+++ b/wp-includes/js/wp-embed.min.js
@@ -1 +1 @@
-!function(c,d){"use strict";var e=!1,n=!1;if(d.querySelector)if(c.addEventListener)e=!0;if(c.wp=c.wp||{},!c.wp.receiveEmbedMessage)if(c.wp.receiveEmbedMessage=function(e){var t=e.data;if(t)if(t.secret||t.message||t.value)if(!/[^a-zA-Z0-9]/.test(t.secret)){for(var r,a,i,s=d.querySelectorAll('iframe[data-secret="'+t.secret+'"]'),n=d.querySelectorAll('blockquote[data-secret="'+t.secret+'"]'),o=0;o<n.length;o++)n[o].style.display="none";for(o=0;o<s.length;o++)if(r=s[o],e.source===r.contentWindow){if(r.removeAttribute("style"),"height"===t.message){if(1e3<(i=parseInt(t.value,10)))i=1e3;else if(~~i<200)i=200;r.height=i}if("link"===t.message)if(a=d.createElement("a"),i=d.createElement("a"),a.href=r.getAttribute("src"),i.href=t.value,i.host===a.host)if(d.activeElement===r)c.top.location.href=t.value}}},e)c.addEventListener("message",c.wp.receiveEmbedMessage,!1),d.addEventListener("DOMContentLoaded",t,!1),c.addEventListener("load",t,!1);function t(){if(!n){n=!0;for(var e,t,r=-1!==navigator.appVersion.indexOf("MSIE 10"),a=!!navigator.userAgent.match(/Trident.*rv:11\./),i=d.querySelectorAll("iframe.wp-embedded-content"),s=0;s<i.length;s++){if(!(e=i[s]).getAttribute("data-secret"))t=Math.random().toString(36).substr(2,10),e.src+="#?secret="+t,e.setAttribute("data-secret",t);if(r||a)(t=e.cloneNode(!0)).removeAttribute("security"),e.parentNode.replaceChild(t,e)}}}}(window,document);
\ No newline at end of file
+!function(d,l){"use strict";var e=!1,n=!1;if(l.querySelector)if(d.addEventListener)e=!0;if(d.wp=d.wp||{},!d.wp.receiveEmbedMessage)if(d.wp.receiveEmbedMessage=function(e){var t=e.data;if(t)if(t.secret||t.message||t.value)if(!/[^a-zA-Z0-9]/.test(t.secret)){for(var r,i,a,s=l.querySelectorAll('iframe[data-secret="'+t.secret+'"]'),n=l.querySelectorAll('blockquote[data-secret="'+t.secret+'"]'),o=new RegExp("^https?:$","i"),c=0;c<n.length;c++)n[c].style.display="none";for(c=0;c<s.length;c++)if(r=s[c],e.source===r.contentWindow){if(r.removeAttribute("style"),"height"===t.message){if(1e3<(a=parseInt(t.value,10)))a=1e3;else if(~~a<200)a=200;r.height=a}if("link"===t.message)if(i=l.createElement("a"),a=l.createElement("a"),i.href=r.getAttribute("src"),a.href=t.value,o.test(a.protocol))if(a.host===i.host)if(l.activeElement===r)d.top.location.href=t.value}}},e)d.addEventListener("message",d.wp.receiveEmbedMessage,!1),l.addEventListener("DOMContentLoaded",t,!1),d.addEventListener("load",t,!1);function t(){if(!n){n=!0;for(var e,t,r=-1!==navigator.appVersion.indexOf("MSIE 10"),i=!!navigator.userAgent.match(/Trident.*rv:11\./),a=l.querySelectorAll("iframe.wp-embedded-content"),s=0;s<a.length;s++){if(!(e=a[s]).getAttribute("data-secret"))t=Math.random().toString(36).substr(2,10),e.src+="#?secret="+t,e.setAttribute("data-secret",t);if(r||i)(t=e.cloneNode(!0)).removeAttribute("security"),e.parentNode.replaceChild(t,e)}}}}(window,document);
\ No newline at end of file
diff --git a/wp-includes/l10n.php b/wp-includes/l10n.php
index 39aa6d498e..8d10ee9817 100644
--- a/wp-includes/l10n.php
+++ b/wp-includes/l10n.php
@@ -139,7 +139,7 @@ function determine_locale() {
 	}
 
 	if ( ! empty( $_GET['wp_lang'] ) && ! empty( $GLOBALS['pagenow'] ) && 'wp-login.php' === $GLOBALS['pagenow'] ) {
-		$determined_locale = sanitize_text_field( $_GET['wp_lang'] );
+		$determined_locale = sanitize_locale_name( wp_unslash( $_GET['wp_lang'] ) );
 	}
 
 	/**
diff --git a/wp-includes/media.php b/wp-includes/media.php
index ace9021fd7..855308c29c 100644
--- a/wp-includes/media.php
+++ b/wp-includes/media.php
@@ -3583,7 +3583,8 @@ function wp_enqueue_media( $args = array() ) {
 		/** This filter is documented in wp-admin/includes/media.php */
 		'captions'         => ! apply_filters( 'disable_captions', '' ),
 		'nonce'            => array(
-			'sendToEditor' => wp_create_nonce( 'media-send-to-editor' ),
+			'sendToEditor'           => wp_create_nonce( 'media-send-to-editor' ),
+			'setAttachmentThumbnail' => wp_create_nonce( 'set-attachment-thumbnail' ),
 		),
 		'post'             => array(
 			'id' => 0,
diff --git a/wp-includes/version.php b/wp-includes/version.php
index 00e97af791..e94e418147 100644
--- a/wp-includes/version.php
+++ b/wp-includes/version.php
@@ -13,7 +13,7 @@
  *
  * @global string $wp_version
  */
-$wp_version = '5.1.15';
+$wp_version = '5.1.16';
 
 /**
  * Holds the WordPress DB revision, increments when changes are made to the WordPress DB schema.