Detect Winlogon Helper DLL in Sumo Logic CSE
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/
Sumo Detection Query
_sourceCategory=*windows* (EventCode=13 OR EventID=13)
| where TargetObject matches "*\\Windows NT\\CurrentVersion\\Winlogon\\*"
| where TargetObject matches "*\\Shell" OR TargetObject matches "*\\Userinit" OR TargetObject matches "*\\Notify" OR TargetObject matches "*\\VmApplet" OR TargetObject matches "*\\AppSetup" OR TargetObject matches "*\\Taskman"
| where !(Details = "explorer.exe" OR Details = "C:\\Windows\\system32\\userinit.exe,")
| parse field=TargetObject "*\\" as RegistryValueName last
| parse field=Image "*\\" as ProcessName last
| table _time, host, TargetObject, RegistryValueName, Details, Image, ProcessName, User
| sort by _time descDetects Sysmon Event ID 13 (registry value set) for Winlogon subkeys associated with Winlogon Helper DLL persistence (T1547.004). Parses the modified value name and initiating process from the log to support analyst triage. Excludes known-good default values for Shell (explorer.exe) and Userinit.
Data Sources
Required Tables
False Positives & Tuning
- Legitimate third-party authentication providers (e.g., Duo Security, RSA SecurID) that inject a credential filter DLL registered via Winlogon Notify
- OS upgrade or repair operations that temporarily replace Shell or Userinit with a setup wrapper
- Automated endpoint imaging pipelines that script Winlogon registry changes during golden image creation
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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