The winbind_name_list_to_sid_string_list function in nsswitch/pam_winbind.c in Samba through 4.1.2 handles invalid require_membership_of group names by accepting authentication by any user, which allows remote authenticated users to bypass intended access restrictions in opportunistic circumstances by leveraging an administrator's pam_winbind configuration-file mistake.
Exploitability
AV:NAC:HAu:SImpact
C:PI:PA:N3.6/AV:N/AC:H/Au:S/C:P/I:P/A:N