Under the category of "you learn something new every day" I was playing around with some stuff yesterday and finally got a chance to confirm something that someone had posted on the ActiveDir mailing list. We all know about how some policies tattoo the registry. Security policies are typically one of those areas where, if you remove a setting, the systems applying that policy are not necessarily reverted back to the prior setting because, well, the system doesn’t necessarily know what the prior setting is. You can imagine that this may be a good idea if by accident you remove a policy that hardens your servers and suddenly the servers decide to revert back to a less restrictive setting.
However, one area that does not follow this model is Restricted Group policy, as I came to discover yesterday. Namely, if I use the part of Restricted Groups called "Members of this Group" to exclusively control the membershp of a particular group, and then remove that policy, the next time that policy is refreshed on the target computer that holds the group, that group’s membership is reverted to the list of members that were there before the policy applies. This is probably documented somewhere but its one of those myriad of things that I hadn’t looked at specifically before and so I thought it was interesting.
Not content with stopping there, I tried one more test. I tried applying the restricted groups policy to an AD group and then removed it to see what the effect would be. Now, I’ve blogged in the past about why using Restricted Groups polciy against AD groups was a bad idea, but this experiment was all about knowledge, so I figured I could break my rules a bit. And what was the result? Well if you guessed that after removing the Restricted Groups policy on an AD group, that the membership would be reverted back to the old one as well, you’d be wrong! Its not too surprising really. First off, I imagine that on computer-based groups, that the membership is probably stored in the local SAM and remains there even when Restricted Groups policy is in place. Its cached, if you will. There is no place for AD to cache group memberships and I’m sure doing so would cause all kinds of issues.