The Ignite Realtime Smack XMPP API 4.x before 4.0.2, and 3.x and 2.x when a custom SSLContext is used, 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.