Winlogon Helper DLL
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. (Citation: Cylance Reg Persistence Sept 2013)
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: (Citation: Cylance Reg Persistence Sept 2013)
* 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.
Mitigations |
|
| Mitigation | Description |
|---|---|
| User Account Management |
Manage the creation, modification, use, and permissions associated to user accounts. |
| Execution Prevention |
Block execution of code on a system through application control, and/or script blocking. |
| Winlogon Helper DLL Mitigation |
Limit the privileges of user accounts so that only authorized administrators can perform Winlogon helper changes. Identify and block potentially malicious software that may be executed through the Winlogon helper process by using whitelisting (Citation: Beechey 2010) tools like AppLocker (Citation: Windows Commands JPCERT) (Citation: NSA MS AppLocker) that are capable of auditing and/or blocking unknown DLLs. |
Detection
Monitor for changes to Registry entries associated with Winlogon that do not correlate with known software, patch cycles, etc. Tools such as Sysinternals Autoruns may also be used to detect system changes that could be attempts at persistence, including listing current Winlogon helper values. (Citation: TechNet Autoruns) New DLLs written to System32 that do not correlate with known good software or patching may also be suspicious. Look for abnormal process behavior that may be due to a process loading a malicious DLL. Data and events should not be viewed in isolation, but as part of a chain of behavior that could lead to other activities, such as network connections made for Command and Control, learning details about the environment through Discovery, and Lateral Movement.
References
- Russinovich, M. (2016, January 4). Autoruns for Windows v13.51. Retrieved June 6, 2016.
- Langendorf, S. (2013, September 24). Windows Registry Persistence, Part 2: The Run Keys and Search-Order. Retrieved April 11, 2018.
- NSA Information Assurance Directorate. (2014, August). Application Whitelisting Using Microsoft AppLocker. Retrieved March 31, 2016.
- Tomonaga, S. (2016, January 26). Windows Commands Abused by Attackers. Retrieved February 2, 2016.
- Beechey, J. (2010, December). Application Whitelisting: Panacea or Propaganda?. Retrieved November 18, 2014.
Связанные риски
Каталоги
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