Detect Hidden Users in CrowdStrike LogScale
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/
LogScale Detection Query
// Hidden User Detection — T1564.002
// Branch 1: Registry modification to SpecialAccounts\UserList
#event_simpleName=RegGenericValueUpdate OR #event_simpleName=RegKeyCreatedValue
| TargetObject = /SpecialAccounts\\UserList/i
| table([_time, ComputerName, UserName, TargetObject, RegValueName, RegValueData, ImageFileName, CommandLine])
// Branch 2: net.exe or net1.exe user add commands
| union (
#event_simpleName=ProcessRollup2
| FileName = /^(net|net1)\.exe$/i
| CommandLine = /user.*/add/i
| table([_time, ComputerName, UserName, FileName, CommandLine, ParentBaseFileName])
)
// Branch 3: New local user account created (Windows Security Event 4720 via Sysmon)
| union (
#event_simpleName=UserAccountCreated
| table([_time, ComputerName, UserName, SubjectUserName, TargetUserName])
)
| sort(field=_time, order=desc)Detects T1564.002 Hidden Users in CrowdStrike Falcon via three detection branches: registry value writes to SpecialAccounts\UserList (which hides accounts from Windows login), net.exe or net1.exe commands adding new user accounts, and UserAccountCreated events indicating new local account provisioning.
Data Sources
Required Tables
False Positives & Tuning
- Windows deployment automation (e.g., MDT, WDS) that creates local accounts using net.exe during OS imaging and hides default service accounts via SpecialAccounts registry keys as part of the image template
- Legitimate system management scripts run by IT administrators that create temporary local accounts for remote support or break-glass access scenarios
- Endpoint security products or privileged access management tools that create local admin accounts with registry-based UI suppression to prevent end-user awareness of the account
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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