The DBD::mysql module through 4.043 for Perl uses the mysql_ssl=1 setting to mean that SSL is optional (even though this setting's documentation has a "your communication with the server will be encrypted" statement), which allows man-in-the-middle attackers to spoof servers via a cleartext-downgrade attack, a related issue to CVE-2015-3152.

ext/mysqlnd/mysqlnd.c in PHP before 5.4.43, 5.5.x before 5.5.27, and 5.6.x before 5.6.11 uses a client SSL option to mean that SSL is optional, which allows man-in-the-middle attackers to spoof servers via a cleartext-downgrade attack, a related issue to CVE-2015-3152.

Oracle MySQL before 5.7.3, Oracle MySQL Connector/C (aka libmysqlclient) before 6.1.3, and MariaDB before 5.5.44 use the --ssl option to mean that SSL is optional, which allows man-in-the-middle attackers to spoof servers via a cleartext-downgrade attack, aka a "BACKRONYM" attack.