Lsass NTLM Authentication Backdoor
How it Works
First, the DLL is injected into the
lsass.exe process, and will begin hooking authentication WinAPI calls. The targeted function is
MsvpPasswordValidate(), located in
NtlmShared.dll. In the pursuit of not being detected, the hooked function will call the original function and allow for the normal flow of authentication. Only after seeing that authentication has failed will the hook swap out the actual NTLM hash with the backdoor hash for comparison.
Nosferatu must be compiled as a 64 bit DLL. It must be injected using the a DLL Injector with SeDebugPrivilege.
You can see it loaded using Procexp:
Login example using Impacket:
In an Active Directory environment, authentication via RDP, runas, or the lock screen does not work with the
nosferatu password. Authentication using SMB, WinRM, and WMI is still possible.
In a non-AD environment, authentication works for all aspects.