There will be a security release of 8.5.x and 8.6.x on February 20th 2019 between 1PM to 5PM America/New York (1800 to 2200 UTC). (To see this in your local timezone, refer to the Drupal Core Calendar) . The risk on this is currently rated at
20/25 (Highly critical) AC:None/A:None/CI:All/II:All/E:Theoretical/TD:Uncommon.
Not all configurations are affected. Reserve time on February 20 during the release window to determine whether your sites are affected and in need of an immediate update. Mitigation information will be included in the advisory.
Contributed module security updates may also be required.
If you are running Drupal 7, no core update is required, but you may need to update contributed modules if you are using an affected module. We are unable to provide the list of those modules at this time.
Neither the Security Team nor any other party is able to release any more information about this vulnerability until the announcement is made. The announcement will be made public at https://www.drupal.org/security, over Twitter, and in email for those who have subscribed to our email list. To subscribe to the email list: log in on Drupal.org, go to your user profile page and subscribe to the security newsletter on the Edit » My newsletters tab.
Security release announcements will appear on the Drupal.org security advisory page.