It was found that Samba before versions 4.5.3, 4.4.8, 4.3.13 always requested forwardable tickets when using Kerberos authentication. A service to which Samba authenticated using Kerberos could subsequently use the ticket to impersonate Samba to other services or domain users.
https://www.samba.org/samba/security/CVE-2016-2125.html
https://bugzilla.redhat.com/show_bug.cgi?id=CVE-2016-2125
https://access.redhat.com/errata/RHSA-2017:1265
http://www.securitytracker.com/id/1037494
http://www.securityfocus.com/bid/94988
http://rhn.redhat.com/errata/RHSA-2017-0744.html
http://rhn.redhat.com/errata/RHSA-2017-0662.html