I thought that CB used those defined in Joomla global parameters, but it's not the case.
In my configuration ; Joomla: 12 characters... CB : 6 characters , with maj, number , special character...
thanks for your answer
Edit the password field in CB > Field Management then under Parameters > Validation you can configure the requirements.
The default value is "empty", which should result in using Joomla general passwords settings, but, when this list box is on empty, actually it chooses (6words+ special...).
The default should be "None", which will use Joomla's settings. So for a new install it should've already been set to that. Existing installs may have already been using one of the other validation rules though.