As per upstream advisory:
All versions of Samba from 4.7.0 onwards are vulnerable to a denial of service attack which can crash the "samba" process when Samba is an Active Directory Domain Controller.
Missing database output checks on the returned directory attributes from the LDB database layer cause the DsCrackNames call in the DRSUAPI server to crash when following a NULL pointer.
This call is only available after authentication.
There is no further vulnerability associated with this error, merely a denial of service.
Created samba tracking bugs for this issue:
Affects: fedora-all [bug 1617910]
Name: Volker Mauel (the Samba project)