Winlogon Helper DLL

What the technique is

Adversaries may abuse features of Winlogon to execute DLLs and/or executables when a user logs in. Winlogon.exe is a Windows component responsible for actions at logon/logoff as well as the secure attention sequence (SAS) triggered by Ctrl-Alt-Delete. Registry entries in HKLM\Software[\\Wow6432Node\\]\Microsoft\Windows NT\CurrentVersion\Winlogon\ and HKCU\Software\Microsoft\Windows NT\CurrentVersion\Winlogon\ are used to manage additional helper programs and functionalities that support Winlogon. Malicious modifications to these Registry keys may cause Winlogon to load and execute malicious DLLs and/or executables. Specifically, the following subkeys have been known to be possibly vulnerable to abuse: Winlogon\Notify - points to notification package DLLs that handle Winlogon events Winlogon\Userinit - points to userinit.exe, the user initialization program executed when a user logs on Winlogon\Shell - points to explorer.exe, the system shell executed when a user logs on Adversaries may take advantage of these features to repeatedly execute malicious code and establish persistence.

What MITRE says you would watch

• AN1133

  Monitor Windows Registry modifications to Winlogon keys (Shell, Userinit, Notify) that introduce new executable or DLL paths. Correlate these changes with subsequent DLL loading, image loads, or process creation originating from winlogon.exe or userinit.exe. Abnormal child process lineage or unauthorized binaries in C:\Windows\System32 may indicate abuse.