Microsoft ISA Server 2006 features role based administration to provide granular access to the ISA firewall configuration and security policies. When configured properly, users who have local administrative rights on the underlying operating system do not implicitly have administrative privileges on the ISA firewall. The security model of the ISA firewall is such that administrative access is defined by the firewall administrator explicitly. However, during the process of installing ISA Server 2006, the BUILTIN\Administrators group, along with the account of the user installing the software is automatically added to the ‘ISA Server Full Administrator’ role. This is done for the obvious reason that someone has to be able to administer the firewall once it is installed!

While this default configuration is good for functionality, it is not particularly ideal for security. The domain administrators group is typically a member of the local administrators group on all domain-joined Windows systems (your ISA firewall should be a member of the domain!). However, do you want all of your domain administrators to have full control over your firewall? In small to mid-sized deployments, perhaps. In larger enterprise deployments, not likely. Now I realize that if you can’t trust your domain administrators you have a serious problem, but I also believe strongly in the principle of least privilege. I would much prefer to keep the number of firewall administrators to a bare minimum.
In my opinion, one of the first things an ISA firewall administrator should do is immediately remove the local administrators group and explicitly define the firewall administrators. In fact, I recommend defining your administrators by their individual user accounts as opposed to using local or domain groups. I prefer this method because it provides more control over who has ISA firewall administrative rights. If you decide to define your ISA firewall administrators by group, be sure to use restricted groups to prevent someone from intentionally or unintentionally adding unnecessary users to the ISA firewall administrators group



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