Windows Process Creation: reg.exe Adds Winlogon SpecialAccounts Userlist Value 0

Flags reg.exe command lines that add SpecialAccounts Userlist with /d 0 to hide accounts from the logon screen.

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windows-process-creation-reg-exe-adds-winlogon-specialaccounts-userlist-value-0-9ec9fb1b

title: "Windows Process Creation: reg.exe Adds Winlogon SpecialAccounts Userlist Value 0"
id: 2bcb6abc-73ae-450f-9fc0-c6d1e8977531
related:
  - id: f8aebc67-a56d-4ec9-9fbe-7b0e8b7b4efd
    type: similar
  - id: 9ec9fb1b-e059-4489-9642-f270c207923d
    type: derived
status: test
description: This rule identifies command-line activity using reg.exe to modify the Winlogon SpecialAccounts Userlist registry value to 0 under HKLM\Software\Microsoft\Windows NT\CurrentVersion\Winlogon\SpecialAccounts\Userlist. Setting this value to 0 can be used to hide a user account from being listed on the logon screen, which helps attackers reduce visibility and persistence artifacts. The detection relies on Windows process creation telemetry capturing the reg.exe image path and the full command line arguments.
references:
  - https://thedfirreport.com/2024/01/29/buzzing-on-christmas-eve-trigona-ransomware-in-3-hours/
  - https://thedfirreport.com/2024/04/01/from-onenote-to-ransomnote-an-ice-cold-intrusion/
  - https://thedfirreport.com/2024/04/29/from-icedid-to-dagon-locker-ransomware-in-29-days/
  - https://thedfirreport.com/2022/07/11/select-xmrig-from-sqlserver/
  - https://github.com/SigmaHQ/sigma/blob/master/rules/windows/process_creation/proc_creation_win_registry_special_accounts_hide_user.yml
author: "@Kostastsale, TheDFIRReport, Huntrule Team"
date: 2022-05-14
modified: 2024-08-23
tags:
  - attack.stealth
  - attack.t1564.002
logsource:
  category: process_creation
  product: windows
detection:
  selection:
    Image|endswith: \reg.exe
    CommandLine|contains|all:
      - \SOFTWARE\Microsoft\Windows NT\CurrentVersion\Winlogon\SpecialAccounts\UserList
      - add
      - /v
      - /d 0
  condition: selection
falsepositives:
  - System administrator activities
level: medium
regression_tests_path: regression_data/rules/windows/process_creation/proc_creation_win_registry_special_accounts_hide_user/info.yml
license: DRL-1.1

What it detects

This rule identifies command-line activity using reg.exe to modify the Winlogon SpecialAccounts Userlist registry value to 0 under HKLM\Software\Microsoft\Windows NT\CurrentVersion\Winlogon\SpecialAccounts\Userlist. Setting this value to 0 can be used to hide a user account from being listed on the logon screen, which helps attackers reduce visibility and persistence artifacts. The detection relies on Windows process creation telemetry capturing the reg.exe image path and the full command line arguments.

Known false positives

System administrator activities

Detection content is published as a reviewed draft. Tune thresholds and exclusions against your own telemetry before enabling this rule for alerting.