Impersonation to get user HKEY_CURRENT_USER does not work?

Question

I am attempting to Impersonate an administrator account from a LocalSystem Service in order to get data from administrators HKEY CURRENT USER registry - in order to impersonate I am using the codeproject code found at the following site written by Uwe Keim: Impersonator

My source code is as follows:

using (new Impersonator("user", ".", "pass"))
{
    RegistryKey rk = Registry.CurrentUser.OpenSubKey("Software\\CompanyName");
    string sValue = rk.GetValue("Value", "").ToString();
    rk2.Close();
}

My expectation was that sValue would be from the user/pass account (as I am impersonating it) but oddly enough it is still the sValue from the LocalSystem account where my service is runnning ...

Any clues on what I am doing wrong? Any help would be much appreciated. Thanks,

Answer 1

I know this is an old thread but I recently came across the same issue (albeit from a C++ Windows service) and thought I'd share my findings, because many forums have asked the same question and none have left a satisfactory answer.

Basically, I've found two ways to approach this, though this is an answer more for C applications rather than .NET (I haven't tested with pinvoke but it may work).

Solution 1: Instead of using RegOpenKey, use RegOpenCurrentUser() to get the key handle. Apparently, the reason RegOpenKey doesn't get the impersonated user's key is because HKEY_CURRENT_USER is cached in the running thread.

Solution 2: RegDisablePredefinedCache(). This disables the cache mentioned above and lets subsequent calls to HKEY_CURRENT_USER be of the actual impersonated user. This is the solution I went with.

Hope this helps.

Answer 2

Everything I've read on the subject seems to indicate that impersonation should get you access to the HKEY_CurrentUser for the impersonated account. However, it could be a quirk in the .NET Registry implementation.

This is just a hunch, and an untested one at that, but have you considered using Registry.Users instead of Registry.CurrentUser?

You'll need to find the SID for the Administrator account, but you should be able to deduce that using Regedit

Answer 3

By default the HKEY_CURRENT_USER handle is cached on a process wide basis. So when you impersonate a user and then access the current user hive you will be accessing the hive of the user that started the process not the user being impersonated. This is true for all Win32 processes not just .Net. If you wish to disable this caching so that all current user calls go to the correct user hive under HKEY_USERS then you must call RegDisablePredefinedCache via pInvoke.

Be warned that if the user being impersonated has not had their profile loaded then any CurrentUser requests will be forwarded to the .DEFAULT user. So you may also need to call LoadUserProfile.

Disabling the handle caching will also cause a slight slowdown in all CurrentUser requests.

Answer 4

I'm guessing you're going to find that you're out of luck. It can't be done.

If applications were able to impersonate an Administrator account and write values to the Registry in Windows, it would present a huge security hole. My guess is that the Registry.CurrentUser property will ALWAYS reference the user running your application...whether or not you try impersonation or not.

EDIT

Turns out that I didn't read the implementation details of the Impersonator code you were using. Your problem could be something completely different.

Does your code refer to the Registry static class prior to your impersonation code being run? If so, that would be the problem. If you look at the Registry.CurrentUser property in Reflector, you'll see that it is set by the static constructor of the Registry object. Static constructors get called when the static object is first referenced.

In your case, if you're referencing the Registry object (whether it involves CurrentUser or not) the static constructor is being called which is setting CurrentUser to your original user...not the Impersonated account.