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.