Question

I have a Windows executable that is launched from within a service by calling CreateProcessWithLogonW() with a set of specfied user details.

This works fine and the process starts as expected. However, when this process tries to launch other processes itself, currently just using CreateProcess() these start then die straight away – they are executables that require desktop access.

After reading up on Microsoft’s article on CreateProcess() – http://msdn.microsoft.com/en-us/library/ms682425(VS.85).aspx

I think can see why this is happening and it makes sense to an extent. CreateProcess() knows the calling process is impersonating a user so it uses it’s parent process, which in this case is the Local System account. But of course anything run in the local system account doesn’t have the access we need, so the launched process dies.

Oddly when I was previously using LogonUser() and CreateProcessAsUser() to launch the initial executable within the service, it worked fine. But I had to change this to CreateProcessWithLogonW() due to problems with not having the correct privileges.

Does anybody know of a solution to this? I’ve seen talk about this elsewhere on the web but not with any definite solution. It seems like I possibly need the token of the user i’m logging on with in CreateProcessWithLogonW() with so I can use it to launch the other processes later? But I have no way of getting hold of this token, can this be retreived for the current user in any way?

Any help would be greatly appreciated, thanks 🙂

Answer 1

Do you own the code launched using CreateProcessWithLogonW (and which in turn calls CreateProcess)? If you do not then you might need to perform IAT (or API) hooking on it (i.e. at run-time), as to substitute any calls to CreateProcess with an appropriate procedure that also uses CreateProcessWithLogonW or CreateProcessWithTokenW. See APIHijack, Detours.

After this is done, the child process may require access to HKCU. If you are not already doing this, you should load the profile of each impersonated user, once per user, before calling CreateProcessWithLogonW.

By default, CreateProcessWithLogonW does not load the specified user profile into the HKEY_USERS registry key. This means that access to information in the HKEY_CURRENT_USER registry key may not produce results that are consistent with a normal interactive logon. It is your responsibility to load the user registry hive into HKEY_USERS before calling CreateProcessWithLogonW, by using LOGON_WITH_PROFILE, or by calling the LoadUserProfile function.