2 days ago, a serious vulnerability, SA-CORE-2018-002 (CVE-2018-7600) has been found in Drupal 6, 7 and 8, which affects over one million websites. All the unpatched Drupals are in serious danger! An attacker can upload backdoors or malware via this newly discovered vulnerability. The vulnerability is scored 21/25 Highly Critical!

Read here for more info and how to proceed: https://www.drupal.org/sa-core-2018-002