This is how UAC works. You will find lots of documentation on UAC but they all forget to mention one thing (below).
If you are a member of the builtin administrators group and try to access a folder that allows this group to do so UAC expects you to access it in an elevated mode. If though your direct account had access to it or any other group did it would work fine (assuming you are a member of it). This issue only seems to affect the special builtin adminstrators group.
So you are meant to acces it in an elevated windows explorer right?? No, it doesn't work. Explorer is the only program that does not work from an elevated prompt, it is bugged.
Full article and work arounds I found here. It took me ages to find it http://think-like-a-computer.com/2011/05/11/uac-access-denied-on-folders-for-administrators-windows-2008/
Update: The original question was for Windows Server 2008, but the solution is easier for Windows Server 2008 R2 and Windows Server 2012 (and Windows 7 and 8). You can add the user through the NTFS UI by typing it in directly. The name is in the format of IIS APPPOOL\{app pool name}. For example: IIS APPPOOL\DefaultAppPool.
IIS APPPOOL\{app pool name}
Note: Per comments below, there are two things to be aware of:
- Enter the string directly into the "Select User or Group" and not in the search field.
- In a domain environment you need to set the Location to your local computer first.
Reference to Microsoft Docs article: Application Pool Identities > Securing Resources
Original response: (for Windows Server 2008) This is a great feature, but as you mentioned it's not fully implemented yet. You can add the app pool identity from the command prompt with something like icacls, then you can manage it from the GUI. For example, run something like this from the command prompt:
icacls c:\inetpub\wwwroot /grant "IIS APPPOOL\DefaultAppPool":(OI)(CI)(RX)
Then, in Windows Explorer, go to the wwwroot folder and edit the security permissions. You will see what looks like a group (the group icon) called DefaultAppPool. You can now edit the permissions.
However, you don't need to use this at all. It's a bonus that you can use if you want. You can use the old way of creating a custom user per app pool and assigning the custom user to disk. That has full UI support.
This SID injection method is nice because it allows you to use a single user but fully isolate each site from each other without having to create unique users for each app pool. Pretty impressive, and it will be even better with UI support.
Note: If you are unable to find the application pool user, check to see if the Windows service called Application Host Helper Service is running. It's the service that maps application pool users to Windows accounts.
Best Answer
Yes, UAC is set up to not allow access to default shares remotely. To enable, create the LocalAccountTokenFilterPolicy DWORD value at this key in the registry
HKLM\SOFTWARE\Microsoft\Windows\CurrentVersion\Policies\system\0 - build filtered token (Remote UAC enabled)
1 - build elevated token (Remote UAC disabled)
By setting the DWORD entry to 1, you will be able to access the administrative shares since the remote logon token will not be filtered.
This is discussed in this KB article, http://support.microsoft.com/kb/947232. (It's for Vista but it applies to Windows Server 2008 R2)