CVE-2016-4745
The Kerberos 5 (aka krb5) PAM module in Apple OS X before 10.12 does not use constant-time operations for determining username validity, which makes it easier for remote attackers to enumerate user accounts via a timing side-channel attack.
Date published : 2016-09-25
http://lists.apple.com/archives/security-announce/2016/Sep/msg00006.html