Samba 4.9.x before 4.9.9 and 4.10.x before 4.10.5 has a NULL pointer dereference, leading to Denial of Service. This is related to the AD DC DNS management server (dnsserver) RPC server process.
The dnsserver task can be stopped by setting
'dcerpc endpoint servers = -dnsserver'
in the smb.conf and restarting Samba.