How to bypass authentication on Windows Server 2008 R2

In this article we will be looking at how easy it is to bypass authentication and reset the administrator password on a Windows Server 2008 R2 installation. This technique requires us to have physical access to the machine that is running the Windows server or have access to the management interface of the hypervisor when Windows Server 2008 R2 is running virtualized. This is not a great ‘hacking’ technique that can be used to pwn all Windows installations but it is more a sysadmins last resort trick when nothing else works on a forgotten password. And in some other situations it is definitely useful and comes in handy when you need it. Especially at the point when you’ve compromised the administration panel of the hypervisor software. This kind of access allows you to control the virtual machines as if you had physical access to it, including the ability to use boot disk and modify system files. Alternatively you can apply this technique when have some kind of physical access to a host.

A couple months ago I was conducting a penetration test on a staged Windows environment that was running on a VMware hypervisor. The environment contained a domain controller and 3 application servers that were running Windows Server 2008 R2. Other then the Windows machines I also encountered a few Linux based network and back-up devices. As it was not very hard to compromise the machines on this network I was able to access the VMware vSphere administration panel as administrator in a very early stage of the penetration test. This access level allowed me to reset the administrator password using a boot CD and finally login to the Windows Server with administrator privileges. In the follow sections I will explain how I did this and how you can secure your Windows installations from applying this technique.

Resetting the administrator password on Windows Server 2008 R2

The starting point of this tutorial is a machine with Windows Server 2008 R2 Enterprise that has been booted with a boot CD. In this example we’ve used the Hiren boot CD (HBCD) but you can use any alternative boot CD as well, including a Windows installation disk. After booting the system from the boot CD navigate to the following directory of the drive that contains the Windows Server 2008 R2 installation:

/Windows/System32

In this directory you will find an executable file named ‘Utilman.exe’. Utilman is a small utility that is used to configure accessibility options such as the magnifier and the on-screen keyboard. What’s so special about Utilman.exe is that we are able to execute this program before logging in the system. We can do this by clicking the small ‘accessibility’ button in the bottom left corner of the Windows logon menu:

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