CKEditor 5 is a modern JavaScript rich-text editor with an MVC architecture. ckeditor5 and ckeditor5-clipboard versions 46.0.0 through 46.0.2 and 44.2.0 through 45.2.1 contain a Cross-Site Scripting (XSS) vulnerability. Ability to exploit could be triggered by a specific user action (leading to unauthorized JavaScript code execution) if the attacker managed to insert a malicious content into the editor, which might happen with a very specific editor configuration. This vulnerability affects installations where the editor configuration meets one of the following criteria: the HTML embed plugin is enabled, or there is a custom plugin introducing an editable element where view RawElement is enabled. This issue is fixed in versions 45.2.2 and 46.0.3 of both ckeditor5 and ckeditor5-clipboard.