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.
https://github.com/perl5-dbi/DBD-mysql/pull/114
https://github.com/perl5-dbi/DBD-mysql/issues/140