Detect Hidden Users in Splunk
Adversaries may use hidden users to hide the presence of user accounts they create or modify. On Windows, accounts can be hidden from the login screen by setting a registry value under HKLM\SOFTWARE\Microsoft\Windows NT\CurrentVersion\Winlogon\SpecialAccounts\UserList with a DWORD value of 0 for the username. On macOS, adversaries can set a user's UID below 500 or set a UserShell property to /usr/bin/false to hide them. Threat actors including Dragonfly, Kimsuky, and SMOKEDHAM malware use hidden user accounts for persistent backdoor access.
MITRE ATT&CK
- Tactic
- Defense Evasion
- Technique
- T1564 Hide Artifacts
- Sub-technique
- T1564.002 Hidden Users
- Canonical reference
- https://attack.mitre.org/techniques/T1564/002/
SPL Detection Query
(index=wineventlog sourcetype="XmlWinEventLog:Microsoft-Windows-Sysmon/Operational" (EventCode=12 OR EventCode=13)
TargetObject="*Winlogon\\SpecialAccounts\\UserList*")
OR
(index=wineventlog sourcetype="WinEventLog:Security" EventCode=4720)
OR
(index=wineventlog sourcetype="WinEventLog:Security" EventCode=4732 Message="*Administrators*")
| eval HiddenUserReg=if(match(TargetObject, "SpecialAccounts"), 1, 0)
| eval UserCreated=if(EventCode=4720, 1, 0)
| eval AddedToAdmins=if(EventCode=4732, 1, 0)
| table _time, host, User, EventCode, TargetObject, Details, Image, Message
| sort - _timeDetects hidden user accounts via Sysmon registry events (EventCode 12/13) for SpecialAccounts/UserList modifications, and Windows Security events for user account creation (4720) and group membership changes (4732). Covering both registry manipulation and account creation provides comprehensive detection.
Data Sources
Required Sourcetypes
False Positives & Tuning
- Administrators configuring service accounts hidden from login screens
- Enterprise management tools creating management accounts
- Built-in Windows service accounts legitimately hidden
- IT staff creating dedicated hidden administrator accounts
Other platforms for T1564.002
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 1Create Hidden User Account via Registry
Expected signal: Windows Security Event ID 4720 (User Account Created) for HiddenTestUser. Sysmon Event ID 13 (Registry Value Set) for the SpecialAccounts key. Security Event ID 4688 for net.exe and reg.exe process creation.
- Test 2Create Hidden Admin User Account
Expected signal: Security Event ID 4720 (user created), 4732 (added to Administrators group), 4688 for net.exe x2 and reg.exe. Sysmon EventCode=13 for SpecialAccounts registry modification.
- Test 3Enumerate Hidden User Accounts
Expected signal: Security Event ID 4688 for reg.exe process creation. The query itself does not create events but identifies existing hidden accounts. No registry write events are generated.
References (4)
- https://attack.mitre.org/techniques/T1564/002/
- https://github.com/redcanaryco/atomic-red-team/blob/master/atomics/T1564.002/T1564.002.md
- https://docs.microsoft.com/en-us/windows/win32/secauthn/winlogon-and-credential-providers
- https://www.mandiant.com/resources/blog/smokedham-backdoor-delivers-cobalt-strike
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