Before I begin this article might be, for some of you, this will be wellÂ knowÂ informationÂ and it might all seem rather logical. But I continue to see questions being asked on forumsÂ as how as a Group Policy administrator can I prevent my users with local admin making a specific change or installing software/drivers onÂ their own computer.
The short answer is you CANT!!!!
You need to think of local administrator are “gods” of their own computers and as such they have the power to do anything on the computer, including overriding any group policies. So, if you knowingly grant local admins for a user to their computer simply assume that you have lost all control of that computer. So always be REALLY sure that the person you are granting local admin access to REALLY has to have that level of access.
Of courseÂ user might not always beÂ tech savvy enough to work around GPO restrictions. But ifÂ they are not, I would really question why you areÂ granting local admin access to that computer in the first place.Â However, if you at least start with that assumption that you have lost control of the computers that you have delegated local admin permission on, then you might take a second thought before actually delegating that access to begin with.
For a more detail explanation as to why this is the case then I recommend you read Mark Russinovich (very old but still relevant) blog post atÂ http://blogs.technet.com/b/markrussinovich/archive/2005/04/30/circumventing-group-policy-settings.aspx . Put simply, a local admin can break group policy by surgically applying permissions to the registry keys of the GPO being applied so that even the SYSTEM account does not have permission to read or change those registry keys. For example if you try to apply permission toÂ prevent users from installing software , or worse drives, then the local admin can override this setting and install software if they know what they are doing.
Also keep in mind that the same applies to the now deprecatedÂ Power Users groupÂ (seeÂ http://blogs.technet.com/b/markrussinovich/archive/2006/05/01/the-power-in-power-users.aspx ) as members of that group have the same effective access as local administrator.
AlsoÂ importantly is to rememberÂ Law 3 of the 10 Immutable Laws of Security “If a bad guy has unrestricted physical access to your computer, it’s not your computer anymore.” whichÂ means that a stolen computer can also be easily compromised.
So, by now you might be thinking thatÂ all is lost… Security is too hard… we should all get new job. Well, not quiet…
Most of these problems can be mitigated if you justÂ ensure users should only run as standard users level of accessÂ and that you have deployed BitLocker (or other full disk encryption software) to your computers. This is fairly common practice now and it does offer good level of confidence that your users, or someone malicious, cannot easily break in to your computers OS’s.
But of course there is no such thing as perfect securityÂ and just doing one or a few things is never enough. For example, malicious users or software can becomeÂ local admin by taking advantage ofÂ local privilege escalation attacks or they can break BitLocker byÂ launching DMA attacks via the FirewireÂ port of your computers.
So when it comes to securing your computersÂ in your environment Group Policy is NEVER then only answer. Instead it should be a part of aÂ multi layered approach to securing your environment.