diff --git a/core/modules/ckeditor5/ckeditor5.module b/core/modules/ckeditor5/ckeditor5.module
index f39dda6ec0..23b2a910d6 100644
--- a/core/modules/ckeditor5/ckeditor5.module
+++ b/core/modules/ckeditor5/ckeditor5.module
@@ -437,6 +437,15 @@ function ckeditor5_library_info_alter(&$libraries, $extension) {
     ];
   }
 
+  if ($extension === 'core') {
+    // CSS rule to resolve the conflict with z-index between CKEditor 5 and jQuery UI.
+    $libraries['drupal.dialog']['css']['component']['modules/ckeditor5/css/ckeditor5.dialog.fix.css'] = [];
+    // Fix the CKEditor 5 focus management in dialogs. Modify the library
+    // declaration to ensure this file is always loaded after
+    // drupal.dialog.jquery-ui.js.
+    $libraries['drupal.dialog']['js']['modules/ckeditor5/js/ckeditor5.dialog.fix.js'] = [];
+  }
+
   // Only add translation processing if the locale module is enabled.
   if (!$moduleHandler->moduleExists('locale')) {
     return;
diff --git a/core/modules/ckeditor5/css/ckeditor5.dialog.fix.css b/core/modules/ckeditor5/css/ckeditor5.dialog.fix.css
new file mode 100644
index 0000000000..b9e0a2e754
--- /dev/null
+++ b/core/modules/ckeditor5/css/ckeditor5.dialog.fix.css
@@ -0,0 +1,3 @@
+.ui-dialog ~ .ck-body-wrapper {
+  --ck-z-modal: 1261;
+}
diff --git a/core/modules/ckeditor5/js/ckeditor5.dialog.fix.es6.js b/core/modules/ckeditor5/js/ckeditor5.dialog.fix.es6.js
new file mode 100644
index 0000000000..14e388ca6a
--- /dev/null
+++ b/core/modules/ckeditor5/js/ckeditor5.dialog.fix.es6.js
@@ -0,0 +1,29 @@
+/**
+ * @file
+ * This file overrides the way jQuery UI focus trap works.
+ *
+ * When a focus event is fired while a CKEditor 5 instance is focused, do not
+ * trap the focus and let CKEditor 5 manage that focus.
+ */
+
+(($) => {
+  // Get core version of the _focusTabbable method.
+  const oldFocusTabbable = $.ui.dialog._proto._focusTabbable;
+
+  $.widget('ui.dialog', $.ui.dialog, {
+    // Override core override of jQuery UI's `_focusTabbable()` so that
+    // CKEditor 5 in modals can work as expected.
+    _focusTabbable() {
+      // When the focused element is a CKEditor 5 instance, disable jQuery UI
+      // focus trap and delegate focus trap to CKEditor 5.
+      const hasFocus = this._focusedElement
+        ? this._focusedElement.get(0)
+        : null;
+      // In case the element is a CKEditor 5 instance, do not change focus
+      // management.
+      if (!(hasFocus && hasFocus.ckeditorInstance)) {
+        oldFocusTabbable.call(this);
+      }
+    },
+  });
+})(jQuery);
diff --git a/core/modules/ckeditor5/js/ckeditor5.dialog.fix.js b/core/modules/ckeditor5/js/ckeditor5.dialog.fix.js
new file mode 100644
index 0000000000..94333b6dcc
--- /dev/null
+++ b/core/modules/ckeditor5/js/ckeditor5.dialog.fix.js
@@ -0,0 +1,19 @@
+/**
+* DO NOT EDIT THIS FILE.
+* See the following change record for more information,
+* https://www.drupal.org/node/2815083
+* @preserve
+**/
+
+(function ($) {
+  var oldFocusTabbable = $.ui.dialog._proto._focusTabbable;
+  $.widget('ui.dialog', $.ui.dialog, {
+    _focusTabbable: function _focusTabbable() {
+      var hasFocus = this._focusedElement ? this._focusedElement.get(0) : null;
+
+      if (!(hasFocus && hasFocus.ckeditorInstance)) {
+        oldFocusTabbable.call(this);
+      }
+    }
+  });
+})(jQuery);
\ No newline at end of file
diff --git a/core/modules/ckeditor5/tests/modules/ckeditor5_test/ckeditor5_test.routing.yml b/core/modules/ckeditor5/tests/modules/ckeditor5_test/ckeditor5_test.routing.yml
index 50d7848984..a7730c0999 100644
--- a/core/modules/ckeditor5/tests/modules/ckeditor5_test/ckeditor5_test.routing.yml
+++ b/core/modules/ckeditor5/tests/modules/ckeditor5_test/ckeditor5_test.routing.yml
@@ -4,3 +4,10 @@ ckeditor5_test.off_canvas:
     _controller: '\Drupal\ckeditor5_test\Controller\CKEditor5OffCanvasTestController::testOffCanvas'
   requirements:
     _access: 'TRUE'
+
+ckeditor5_test.dialog:
+  path: '/ckeditor5_test/dialog'
+  defaults:
+    _controller: '\Drupal\ckeditor5_test\Controller\CKEditor5DialogTestController::testDialog'
+  requirements:
+    _access: 'TRUE'
diff --git a/core/modules/ckeditor5/tests/modules/ckeditor5_test/src/Controller/CKEditor5DialogTestController.php b/core/modules/ckeditor5/tests/modules/ckeditor5_test/src/Controller/CKEditor5DialogTestController.php
new file mode 100644
index 0000000000..2eed8d56b9
--- /dev/null
+++ b/core/modules/ckeditor5/tests/modules/ckeditor5_test/src/Controller/CKEditor5DialogTestController.php
@@ -0,0 +1,44 @@
+<?php
+
+declare(strict_types = 1);
+
+namespace Drupal\ckeditor5_test\Controller;
+
+use Drupal\Component\Serialization\Json;
+use Drupal\Core\Url;
+
+/**
+ * Provides controller for testing CKEditor in off-canvas dialogs.
+ */
+class CKEditor5DialogTestController {
+
+  /**
+   * Returns a link that can open a node add form in an modal dialog.
+   *
+   * @return array
+   *   A render array.
+   */
+  public function testDialog() {
+    $build['link'] = [
+      '#type' => 'link',
+      '#title' => 'Add Node',
+      '#url' => Url::fromRoute('node.add', ['node_type' => 'page']),
+      '#attributes' => [
+        'class' => ['use-ajax'],
+        'data-dialog-type' => 'dialog',
+        'data-dialog-options' => Json::encode([
+          'width' => 700,
+          'modal' => TRUE,
+          'autoResize' => TRUE,
+        ]),
+      ],
+    ];
+    $build['#attached']['library'][] = 'core/drupal.dialog.ajax';
+    // Add this library to prevent Modernizr from triggering a deprecation
+    // notice during testing.
+    // @todo remove in https://www.drupal.org/project/drupal/issues/3269082.
+    $build['#attached']['library'][] = 'core/drupal.touchevents-test';
+    return $build;
+  }
+
+}
diff --git a/core/modules/ckeditor5/tests/src/FunctionalJavascript/CKEditor5DialogTest.php b/core/modules/ckeditor5/tests/src/FunctionalJavascript/CKEditor5DialogTest.php
new file mode 100644
index 0000000000..9f2f97536a
--- /dev/null
+++ b/core/modules/ckeditor5/tests/src/FunctionalJavascript/CKEditor5DialogTest.php
@@ -0,0 +1,84 @@
+<?php
+
+namespace Drupal\Tests\ckeditor5\FunctionalJavascript;
+
+use Drupal\ckeditor5\Plugin\Editor\CKEditor5;
+use Drupal\editor\Entity\Editor;
+use Drupal\filter\Entity\FilterFormat;
+use Drupal\Tests\ckeditor5\Traits\CKEditor5TestTrait;
+use Drupal\user\RoleInterface;
+use Symfony\Component\Validator\ConstraintViolation;
+
+/**
+ * Tests for CKEditor 5 to ensure correct focus management in dialogs.
+ *
+ * @group ckeditor5
+ * @internal
+ */
+class CKEditor5DialogTest extends CKEditor5TestBase {
+
+  use CKEditor5TestTrait;
+
+  /**
+   * {@inheritdoc}
+   */
+  protected static $modules = [
+    'node',
+    'ckeditor5',
+    'ckeditor5_test',
+  ];
+
+  /**
+   * Tests if CKEditor 5 tooltips can be interacted with in dialogs.
+   */
+  public function testCKEditor5FocusInTooltipsInDialog() {
+    FilterFormat::create([
+      'format' => 'test_format',
+      'name' => 'CKEditor 5 with link',
+      'roles' => [RoleInterface::AUTHENTICATED_ID],
+    ])->save();
+    Editor::create([
+      'format' => 'test_format',
+      'editor' => 'ckeditor5',
+      'settings' => [
+        'toolbar' => [
+          'items' => ['link'],
+        ],
+      ],
+    ])->save();
+
+    $this->assertSame([], array_map(
+      function (ConstraintViolation $v) {
+        return (string) $v->getMessage();
+      },
+      iterator_to_array(CKEditor5::validatePair(
+        Editor::load('test_format'),
+        FilterFormat::load('test_format')
+      ))
+    ));
+
+    $page = $this->getSession()->getPage();
+    $assert_session = $this->assertSession();
+
+    $this->drupalGet('/ckeditor5_test/dialog');
+    $page->clickLink('Add Node');
+    $assert_session->waitForElementVisible('css', '[role="dialog"]');
+    $assert_session->assertWaitOnAjaxRequest();
+
+    $content_area = $assert_session->waitForElementVisible('css', '.ck-editor__editable');
+    // Focus the editable area first.
+    $content_area->click();
+    // Then press the button to add a link.
+    $this->pressEditorButton('Link');
+
+    $link_url = '/ckeditor5_test/dialog';
+    $input = $assert_session->waitForElementVisible('css', '.ck-balloon-panel input.ck-input-text');
+    // Make sure the input field can have focus and we can type into it.
+    $input->setValue($link_url);
+    // Save the new link.
+    $page->find('css', '.ck-balloon-panel .ck-button-save')->click();
+    // Make sure something was added to the text.
+    $this->assertNotEmpty($content_area->getText());
+  }
+
+}