From National Cyber Awareness System:

Mozilla Releases Security Update
08/21/2017 07:32 AM EDT

Original release date: August 21, 2017

Mozilla has released a security update to address multiple vulnerabilities in Thunderbird.  A remote attacker could exploit some of these vulnerabilities to take control of an affected system.

US-CERT encourages users and administrators to review the Mozilla Security Advisory for Thunderbird 52.3 and apply the necessary update.