According to latest news, there is a security flaw in postfix.
As far as I can see, ISPConfig systems are not affected by this problem, because they use procmail as LDA and not postfix local delivery. Additionally, all current setups that are based on the perfect setup guide use Maildir for storing mails and Maildir is not affected (independant if procmail is used as lda or not).
Here is the security bulletin and explanation from the postfix developers:
Nevertheless you should install ne postfix packages from your linux distribution when they become available.