Apr 19, 12:06 PDT
Resolved – Drupal.org has released version 8.3.1. This release is classified as a highly critical security release. Pantheon has made the update available for one-click update in site dashboards. Instructions for applying core updates can be found in our Support Center. This release addresses the SA-2017-002; all users are urged to upgrade their sites as soon as possible.
 – https://www.drupal.org/project/drupal/releases/8.3.1
 – http://helpdesk.getpantheon.com/customer/portal/articles/361248
 – https://www.drupal.org/SA-CORE-2017-002