x3270 before 3.3.12ga12 does not verify that the server hostname matches a domain name in the subject's Common Name (CN) or subjectAltName field of the X.509 certificate, which allows man-in-the-middle attackers to spoof SSL servers via an arbitrary valid certificate.
https://exchange.xforce.ibmcloud.com/vulnerabilities/82984
https://bugzilla.redhat.com/show_bug.cgi?id=889373
http://sourceforge.net/projects/x3270/files/x3270/3.3.12ga12/