The GnuTLS backend in libcurl 7.21.4 through 7.33.0, when disabling digital signature verification (CURLOPT_SSL_VERIFYPEER), also disables the CURLOPT_SSL_VERIFYHOST check for CN or SAN host name fields, which makes it easier for remote attackers to spoof servers and conduct man-in-the-middle (MITM) attacks.
https://h20564.www2.hp.com/hpsc/doc/public/display?docId=emr_na-c04463322
http://www.ubuntu.com/usn/USN-2058-1
http://www.oracle.com/technetwork/topics/security/cpujul2015-2367936.html