Apple Online Store Kit in Apple OS X before 10.11 improperly validates iCloud keychain item ACLs, which allows attackers to obtain access to keychain items via a crafted app.
https://support.apple.com/HT205267
http://www.securitytracker.com/id/1033703
http://lists.apple.com/archives/security-announce/2015/Sep/msg00008.html