"CKEditor, a third-party JavaScript library included in Drupal core, has fixed a cross-site scripting (XSS) vulnerability. The vulnerability stemmed from the fact that it was possible to execute XSS inside CKEditor when using the image2 plugin (which Drupal 8 core also uses)."
"This Public Service Announcement is a follow-up to SA-CORE-2018-002 - Drupal core - RCE. This is not an announcement of a new vulnerability. If you have not updated your site as described in SA-CORE-2018-002 you should assume your site has been targeted and follow directions for remediation..." in this post.