Detect Winlogon Helper DLL in CrowdStrike LogScale
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\Microsoft\Windows NT\CurrentVersion\Winlogon\ and HKCU\Software\Microsoft\Windows NT\CurrentVersion\Winlogon\ are used to manage additional helper programs. Malicious modifications to these Registry keys may cause Winlogon to load and execute malicious DLLs and/or executables. Specifically, the Winlogon\Notify, Winlogon\Userinit, and Winlogon\Shell subkeys are known targets for abuse by threat actors including Turla, Wizard Spider, and LockBit.
MITRE ATT&CK
- Tactic
- Persistence Privilege Escalation
- Technique
- T1547 Boot or Logon Autostart Execution
- Sub-technique
- T1547.004 Winlogon Helper DLL
- Canonical reference
- https://attack.mitre.org/techniques/T1547/004/
LogScale Detection Query
#event_simpleName = /AsepValueUpdate|RegGenericValueUpdate/
| TargetObject = /\\Windows NT\\CurrentVersion\\Winlogon\\/
| TargetValueName = /^(Shell|Userinit|Notify|VmApplet|AppSetup|Taskman)$/
| !(TargetValueName = "Shell" AND TargetValueData = "explorer.exe")
| !(TargetValueName = "Userinit" AND TargetValueData = /C:\\Windows\\system32\\userinit\.exe,/i)
| ImageFileName match /\\([^\\]+)$/ as ProcessName
| groupBy([ComputerName, ProcessName, TargetObject, TargetValueName, TargetValueData, UserName], function=count(as=EventCount))
| sort(EventCount, order=desc)Detects CrowdStrike Falcon AsepValueUpdate or RegGenericValueUpdate events targeting Winlogon registry subkeys. Groups results by host, process, key, and value to surface repeated writes from the same process. Excludes known-good Shell and Userinit defaults to reduce alert fatigue. Covers MITRE ATT&CK T1547.004 persistence via Winlogon Helper DLL.
Data Sources
Required Tables
False Positives & Tuning
- Legitimate endpoint security agents registered as Winlogon Notify DLLs (e.g., Carbon Black, older Symantec Endpoint Protection versions) that update their own registry entries
- Group Policy refresh operations on domain-joined machines that rewrite Winlogon values to enforce policy-defined defaults
- Software deployment tools (SCCM, Intune Win32 apps) running as SYSTEM that set a custom Userinit wrapper during application layering or VDI provisioning
Other platforms for T1547.004
Testing Methodology
Validate this detection against 3 adversary techniques from Atomic Red Team. Each test below lists the behaviour to exercise and the telemetry you should expect to see. Executable commands and cleanup steps are available with Pro.
- Test 1Modify Winlogon Shell to Append Malicious Binary
Expected signal: Sysmon Event ID 13: RegistryValueSet on HKCU\...\Winlogon\Shell with value containing 'explorer.exe, C:\Windows\System32\calc.exe'.
- Test 2Modify Winlogon Userinit to Chain Malicious Binary
Expected signal: Sysmon Event ID 13: RegistryValueSet on HKLM\...\Winlogon\Userinit showing the appended executable path.
- Test 3Create Winlogon Notify Key
Expected signal: Sysmon Event ID 12: Key created for the Notify subkey. Sysmon Event ID 13: Value set for DllName.
References (4)
- https://attack.mitre.org/techniques/T1547/004/
- https://web.archive.org/web/20160214140250/http://blog.cylance.com/windows-registry-persistence-part-2-the-run-keys-and-search-order
- https://technet.microsoft.com/en-us/sysinternals/bb963902
- https://github.com/redcanaryco/atomic-red-team/blob/master/atomics/T1547.004/T1547.004.md
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