diff -r 34716fd837a4 -r be944660c56a wp/wp-admin/js/custom-background.js
--- a/wp/wp-admin/js/custom-background.js	Tue Dec 15 15:52:01 2020 +0100
+++ b/wp/wp-admin/js/custom-background.js	Wed Sep 21 18:19:35 2022 +0200
@@ -12,7 +12,7 @@
  * @requires jQuery
  */
 (function($) {
-	$(document).ready(function() {
+	$( function() {
 		var frame,
 			bgImage = $( '#custom-background-image' );
 
@@ -39,7 +39,7 @@
 		 *
 		 * @return {void}
 		 */
-		$( 'select[name="background-size"]' ).change( function() {
+		$( 'select[name="background-size"]' ).on( 'change', function() {
 			bgImage.css( 'background-size', $( this ).val() );
 		});
 
@@ -50,7 +50,7 @@
 		 *
 		 * @return {void}
 		 */
-		$( 'input[name="background-position"]' ).change( function() {
+		$( 'input[name="background-position"]' ).on( 'change', function() {
 			bgImage.css( 'background-position', $( this ).val() );
 		});
 
@@ -61,7 +61,7 @@
 		 *
 		 * @return {void}
 		 */
-		$( 'input[name="background-repeat"]' ).change( function() {
+		$( 'input[name="background-repeat"]' ).on( 'change',  function() {
 			bgImage.css( 'background-repeat', $( this ).is( ':checked' ) ? 'repeat' : 'no-repeat' );
 		});
 
@@ -72,7 +72,7 @@
 		 *
 		 * @return {void}
 		 */
-		$( 'input[name="background-attachment"]' ).change( function() {
+		$( 'input[name="background-attachment"]' ).on( 'change', function() {
 			bgImage.css( 'background-attachment', $( this ).is( ':checked' ) ? 'scroll' : 'fixed' );
 		});
 
@@ -83,7 +83,7 @@
 		 *
 		 * @return {void}
 		 */
-		$('#choose-from-library-link').click( function( event ) {
+		$('#choose-from-library-link').on( 'click', function( event ) {
 			var $el = $(this);
 
 			event.preventDefault();
@@ -126,11 +126,13 @@
 			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.