CVE-2018-16857

It was found that the ‘bad password observation window’ was ineffective when set to a value greater than 3 minutes. This could allow for brute force password attacks in some situations.

Mitigation

Bad password lockout is not configured by default, it is only
effective if a threshold has been set with (eg):

samba-tool domain passwordsettings set --account-lockout-threshold=3

To mitigate the issue set a shorter 'Reset account lockout after'
window (the ineffective default is 30, anything less than 15 will
work):

samba-tool domain passwordsettings set --reset-account-lockout-after=15

NOTE: If a fine-grained password policy (PSO) is set, this must also
be done on each PSO.