Multiple security issues were discovered in MySQL and this update includes new upstream MySQL versions to fix these issues.
MySQL has been updated to 5.5.61 in Ubuntu 14.04 LTS. Ubuntu 16.04 LTS and Ubuntu 18.04 LTS have been updated to MySQL 5.7.23.
In addition to security fixes, the updated packages contain bug fixes, new features, and possibly incompatible changes.
Please see the following for more information: <http://dev.mysql.com/doc/relnotes/mysql/5.5/en/news-5-5-61.html> <http://dev.mysql.com/doc/relnotes/mysql/5.7/en/news-5-7-23.html> <http://www.oracle.com/technetwork/security-advisory/cpujul2018-4258247.html>