As per upstream:
The Samba routine ndr_pull_dnsp_name contains an integer wrap problem, leading to an attacker-controlled memory overwrite. ndr_pull_dnsp_name parses data from the Samba Active Directory ldb database. Any user who can write to the dnsRecord attribute over LDAP can trigger this memory corruption.
By default, all authenticated LDAP users can write to the dnsRecord attribute on new DNS objects. This makes the defect a remote privilege escalation.
Red Hat Enterprise Linux 5, 6 and 7 are not affected by this flaw because we do not ship Samba with the AD DNS Server, which is the vulnerable component.