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T1547.004 Winlogon Helper DLL

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.1

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: 1

  • 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.

Item Value
ID T1547.004
Sub-techniques T1547.001, T1547.002, T1547.003, T1547.004, T1547.005, T1547.006, T1547.007, T1547.008, T1547.009, T1547.010, T1547.012, T1547.013, T1547.014, T1547.015
Tactics TA0003, TA0004
CAPEC ID CAPEC-579
Platforms Windows
Permissions required Administrator, SYSTEM
Version 1.0
Created 24 January 2020
Last Modified 20 April 2022

Procedure Examples

ID Name Description
S0534 Bazar Bazar can use Winlogon Helper DLL to establish persistence.12
S0351 Cannon Cannon adds the Registry key HKCU\Software\Microsoft\Windows NT\CurrentVersion\Winlogon to establish persistence.11
S0200 Dipsind A Dipsind variant registers as a Winlogon Event Notify DLL to establish persistence.9
S0168 Gazer Gazer can establish persistence by setting the value “Shell” with “explorer.exe, %malware_pathfile%” under the Registry key HKCU\Software\Microsoft\Windows NT\CurrentVersion\Winlogon.10
S0387 KeyBoy KeyBoy issues the command reg add “HKLM\SOFTWARE\Microsoft\Windows NT\CurrentVersion\Winlogon” to achieve persistence.7 8
S0375 Remexi Remexi achieves persistence using Userinit by adding the Registry key HKLM\Software\Microsoft\Windows NT\CurrentVersion\Winlogon\Userinit.6
G0081 Tropic Trooper Tropic Trooper has created the Registry key HKCU\Software\Microsoft\Windows NT\CurrentVersion\Winlogon\Shell and sets the value to establish persistence.1314
G0010 Turla Turla established persistence by adding a Shell value under the Registry key HKCU\Software\Microsoft\Windows NT\CurrentVersion\Winlogon.16
G0102 Wizard Spider Wizard Spider has established persistence using Userinit by adding the Registry key HKLM\SOFTWARE\Microsoft\Windows NT\CurrentVersion\Winlogon.15

Mitigations

ID Mitigation Description
M1038 Execution Prevention Identify and block potentially malicious software that may be executed through the Winlogon helper process by using application control 3 tools like AppLocker 4 5 that are capable of auditing and/or blocking unknown DLLs.
M1018 User Account Management Limit the privileges of user accounts so that only authorized administrators can perform Winlogon helper changes.

Detection

ID Data Source Data Component
DS0017 Command Command Execution
DS0011 Module Module Load
DS0024 Windows Registry Windows Registry Key Modification

References

  1. Langendorf, S. (2013, September 24). Windows Registry Persistence, Part 2: The Run Keys and Search-Order. Retrieved April 11, 2018. ↩↩

  2. Russinovich, M. (2016, January 4). Autoruns for Windows v13.51. Retrieved June 6, 2016. ↩

  3. Beechey, J. (2010, December). Application Whitelisting: Panacea or Propaganda?. Retrieved November 18, 2014. ↩

  4. Tomonaga, S. (2016, January 26). Windows Commands Abused by Attackers. Retrieved February 2, 2016. ↩

  5. NSA Information Assurance Directorate. (2014, August). Application Whitelisting Using Microsoft AppLocker. Retrieved March 31, 2016. ↩

  6. Legezo, D. (2019, January 30). Chafer used Remexi malware to spy on Iran-based foreign diplomatic entities. Retrieved April 17, 2019. ↩

  7. Parys, B. (2017, February 11). The KeyBoys are back in town. Retrieved June 13, 2019. ↩

  8. Hulcoop, A., et al. (2016, November 17). It’s Parliamentary KeyBoy and the targeting of the Tibetan Community. Retrieved June 13, 2019. ↩

  9. Windows Defender Advanced Threat Hunting Team. (2016, April 29). PLATINUM: Targeted attacks in South and Southeast Asia. Retrieved February 15, 2018. ↩

  10. ESET. (2017, August). Gazing at Gazer: Turla’s new second stage backdoor. Retrieved September 14, 2017. ↩

  11. Falcone, R., Lee, B. (2018, November 20). Sofacy Continues Global Attacks and Wheels Out New ‘Cannon’ Trojan. Retrieved November 26, 2018. ↩

  12. Sadique, M. and Singh, A. (2020, September 29). Spear Phishing Campaign Delivers Buer and Bazar Malware. Retrieved November 19, 2020. ↩

  13. Ray, V. (2016, November 22). Tropic Trooper Targets Taiwanese Government and Fossil Fuel Provider With Poison Ivy. Retrieved November 9, 2018. ↩

  14. Chen, J.. (2020, May 12). Tropic Trooper’s Back: USBferry Attack Targets Air gapped Environments. Retrieved May 20, 2020. ↩

  15. Kimberly Goody, Jeremy Kennelly, Joshua Shilko, Steve Elovitz, Douglas Bienstock. (2020, October 28). Unhappy Hour Special: KEGTAP and SINGLEMALT With a Ransomware Chaser. Retrieved October 28, 2020. ↩

  16. ESET, et al. (2018, January). Diplomats in Eastern Europe bitten by a Turla mosquito. Retrieved July 3, 2018. ↩

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