Backdooring the login screen/RDP

With physical access to the machine (or RDP in our case), you can backdoor the login screen to access a terminal without having valid credentials for a machine.

Sticky Keys

When pressing key combinations like CTRL+ALT+DEL, you can configure Windows to use sticky keys, which allows you to press the buttons of a combination sequentially instead of at the same time. In that sense, if sticky keys are active, you could press and release CTRL, press and release ALT and finally, press and release DEL to achieve the same effect as pressing the CTRL+ALT+DEL combination.

To establish persistence using Sticky Keys, we can abuse a shortcut enabled by default in any Windows installation that allows us to activate Sticky Keys by pressing SHIFT 5 times after which Windows will execute the binary in C:\Windows\System32\sethc.exe.

If we replace the binary with a payload, we can then trigger it with the shortcut. We can even do this from the login screen before entering any credentials.

We can replace sethc.exe with a copy of cmd.exe to spawn a console using the sticky keys shortcut, even from the login screen. To overwrite sethc.exe, we first need to take ownership of it and grant the current user permission to modify it.

takeown /f c:\Windows\System32\sethc.exe
icacls C:\Windows\System32\sethc.exe /grant Administrator:F
copy c:\Windows\System32\cmd.exe C:\Windows\System32\sethc.exe

Lock the current session from the start menu, and press SHIFT 5 times to access a terminal with SYSTEM privileges directly from the login screen.


Utilman is a built-in Windows application used to provide Ease of Access options during the lock screen. When clicking the ease of access button on the login screen, it executes C:\Windows\System32\Utilman.exe with SYSTEM privileges. Replacing it with a copy of cmd.exe, we can bypass the login screen again.

To replace utilman.exe:

takeown /f c:\Windows\System32\utilman.exe
icacls C:\Windows\System32\utilman.exe /grant Administrator:F
copy c:\Windows\System32\cmd.exe C:\Windows\System32\utilman.exe

To trigger the terminal, lock the screen from the start button, and click on the “Ease of Access” button.