Samba 4.10.x before 4.10.5 has a NULL pointer dereference, leading to an AD DC LDAP server Denial of Service. This is related to an attacker using the paged search control. The attacker must have directory read access in order to attempt an exploit.
https://www.synology.com/security/advisory/Synology_SA_19_27
https://www.samba.org/samba/security/CVE-2019-12436.html