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ATT&CK Technique

Winlogon Helper DLL

T1547.004 · persistence, privilege-escalation

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[\\Wow6432Node\\]\Microsoft\Windows NT\CurrentVersion\Winlogon\ and HKCU\Software\Microsoft\Windows NT\CurrentVersion\Winlogon\ are used to manage additional helper programs and functionalities that support Winlogon.

Malicious modifications to these Registry keys may cause Winlogon to load and execute malicious DLLs and/or executables. Specifically, the following subkeys have been known to be possibly vulnerable to abuse: Winlogon\Notify - points to notification package DLLs that handle Winlogon events Winlogon\Userinit - points to userinit.exe, the user initialization program executed when a user logs on * Winlogon\Shell - points to explorer.exe, the system shell executed when a user logs on Adversaries may take advantage of these features to repeatedly execute malicious code and establish persistence.

Windows
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Actors Using This

4
brazilBanbra
brazilBizarro
us_israel_joint_offensive_cyberStuxnet
russiaTurla
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Likely Attack Path

Techniques the same actors pair with this one distinctively - those showing up among actors who use this technique noticeably more than across all actors (lift > 1.15), grouped by kill-chain phase. The × is that lift multiplier; the shared-actor count is in the tooltip. A near-universal technique pairs with everything at baseline, so its list is short by design.
resource-development earlier
T1588.001 · Malware ×1.35
initial-access earlier
T1189 · Drive-by Compromise ×2.38
execution earlier
T1106 · Native API ×1.42T1059.007 · JavaScript ×1.31
credential-access later
T1555.003 · Credentials from Web Browsers ×1.39
discovery later
T1010 · Application Window Discovery ×1.49T1518.001 · Security Software Discovery ×1.46
collection later
T1056.004 · Credential API Hooking ×19.83T1115 · Clipboard Data ×2.03T1113 · Screen Capture ×1.70T1056 · Input Capture ×1.34
impact later
T1565.002 · Transmitted Data Manipulation ×13.22T1565.001 · Stored Data Manipulation ×7.44T1565 · Data Manipulation ×6.26
other same
T1564 · Hide Artifacts ×2.23
▸

Atomic Tests

5
Executable Atomic Red Team test cases for exercising this technique in a lab. Copy a command, run it on the listed platform, confirm your detections fire.
powershellwindowsWinlogon Shell Key Persistence - PowerShell
PowerShell code to set Winlogon shell key to execute a binary at logon along with explorer.exe. Upon successful execution, PowerShell will modify a registry value to execute cmd.exe upon logon/logoff. 
Set-ItemProperty "HKCU:\Software\Microsoft\Windows NT\CurrentVersion\Winlogon\" "Shell" "explorer.exe, #{binary_to_execute}" -Force
powershellwindowsWinlogon Userinit Key Persistence - PowerShell
PowerShell code to set Winlogon userinit key to execute a binary at logon along with userinit.exe. Upon successful execution, PowerShell will modify a registry value to execute cmd.exe upon logon/logoff. 
Set-ItemProperty "HKCU:\Software\Microsoft\Windows NT\CurrentVersion\Winlogon\" "Userinit" "Userinit.exe, #{binary_to_execute}" -Force
powershellwindowsWinlogon Notify Key Logon Persistence - PowerShell
PowerShell code to set Winlogon Notify key to execute a notification package DLL at logon. Upon successful execution, PowerShell will modify a registry value to execute atomicNotificationPackage.dll upon logon. Please note that Winlogon Notifications have been removed as of Windows Vista / Windows Server 2008 and that this test thus only applies to erlier versions of Windows. 
New-Item "HKCU:\Software\Microsoft\Windows NT\CurrentVersion\Winlogon\Notify\AtomicRedTeam" -Force
Set-ItemProperty "HKCU:\Software\Microsoft\Windows NT\CurrentVersion\Winlogon\Notify\AtomicRedTeam" "DllName" "#{binary_to_execute}" -Type ExpandString -Force
Set-ItemProperty "HKCU:\Software\Microsoft\Windows NT\CurrentVersion\Winlogon\Notify\AtomicRedTeam" "Logon" "#{function_to_execute}" -Force
Set-ItemProperty "HKCU:\Software\Microsoft\Windows NT\CurrentVersion\Winlogon\Notify\AtomicRedTeam" "Impersonate" 1 -Type DWord -Force
Set-ItemProperty "HKCU:\Software\Microsoft\Windows NT\CurrentVersion\Winlogon\Notify\AtomicRedTeam" "Asynchronous" 0 -Type DWord -Force
powershellwindowsWinlogon HKLM Shell Key Persistence - PowerShell
PowerShell code to set Winlogon shell key to execute a binary at logon along with explorer.exe. Upon successful execution, PowerShell will modify a registry value to execute cmd.exe upon logon/logoff. 
Set-ItemProperty "HKLM:\Software\Microsoft\Windows NT\CurrentVersion\Winlogon\" "Shell" "explorer.exe, #{binary_to_execute}" -Force
powershellwindowsWinlogon HKLM Userinit Key Persistence - PowerShell
PowerShell code to set Winlogon userinit key to execute a binary at logon along with userinit.exe. Upon successful execution, PowerShell will modify a registry value to execute cmd.exe upon logon/logoff. 
Set-ItemProperty "HKLM:\Software\Microsoft\Windows NT\CurrentVersion\Winlogon\" "Userinit" "Userinit.exe, #{binary_to_execute}" -Force
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Mitigations

2
MITRE ATT&CK mitigations - vendor-agnostic guidance for reducing exposure to this technique.
M1018User Account Management

User Account Management involves implementing and enforcing policies for the lifecycle of user accounts, including creation, modification, and deactivation. Proper account management reduces the attack surface by limiting unauthorized access, managing account privileges, and ensuring accounts are used according to organizational policies.

Enforcing the Principle of Least Privilege
  • Implementation: Assign users only the minimum permissions required to perform their job functions. Regularly audit accounts to ensure no excess permissions are granted.
  • Use Case: Reduces the risk of privilege escalation by ensuring accounts cannot perform unauthorized actions. Implementing Strong Password Policies.
  • Implementation: Enforce password complexity requirements (e.g., length, character types). Require password expiration every 90 days and disallow password reuse.
  • Use Case: Prevents adversaries from gaining unauthorized access through password guessing or brute force attacks. Managing Dormant and Orphaned Accounts.
  • Implementation: Implement automated workflows to disable accounts after a set period of inactivity (e.g., 30 days). Remove orphaned accounts (e.g., accounts without an assigned owner) during regular account audits.
  • Use Case: Eliminates dormant accounts that could be exploited by attackers. Account Lockout Policies.
  • Implementation: Configure account lockout thresholds (e.g., lock accounts after five failed login attempts). Set lockout durations to a minimum of 15 minutes.
  • Use Case: Mitigates automated attack techniques that rely on repeated login attempts. Multi-Factor Authentication (MFA) for High-Risk Accounts.
  • Implementation: Require MFA for all administrative accounts and high-risk users. Use MFA mechanisms like hardware tokens, authenticator apps, or biometrics.
  • Use Case: Prevents unauthorized access, even if credentials are stolen. Restricting Interactive Logins.
  • Implementation: Restrict interactive logins for privileged accounts to specific secure systems or management consoles. Use group policies to enforce logon restrictions.
  • Use Case: Protects sensitive accounts from misuse or exploitation.
Tools for Implementation Built-in Tools
  • Microsoft Active Directory (AD): Centralized account management and RBAC enforcement.
  • Group Policy Object (GPO): Enforce password policies, logon restrictions, and account lockout policies.
Identity and Access Management (IAM) Tools
  • Okta: Centralized user provisioning, MFA, and SSO integration.
  • Microsoft Azure Active Directory: Provides advanced account lifecycle management, role-based access, and conditional access policies.
Privileged Account Management (PAM)
  • CyberArk, BeyondTrust, Thycotic: Manage and monitor privileged account usage, enforce session recording, and JIT access.
M1038Execution Prevention

Prevent the execution of unauthorized or malicious code on systems by implementing application control, script blocking, and other execution prevention mechanisms. This ensures that only trusted and authorized code is executed, reducing the risk of malware and unauthorized actions.

Application Control
  • Use Case: Use tools like AppLocker or Windows Defender Application Control (WDAC) to create whitelists of authorized applications and block unauthorized ones. On Linux, use tools like SELinux or AppArmor to define mandatory access control policies for application execution.
  • Implementation: Allow only digitally signed or pre-approved applications to execute on servers and endpoints. (e.g., `New-AppLockerPolicy -PolicyType Enforced -FilePath "C:\Policies\AppLocker.
xml"`) Script Blocking
  • Use Case: Use script control mechanisms to block unauthorized execution of scripts, such as PowerShell or JavaScript. Web Browsers: Use browser extensions or settings to block JavaScript execution from untrusted sources.
  • Implementation: Configure PowerShell to enforce Constrained Language Mode for non-administrator users. (e.g.
, Set-ExecutionPolicy AllSigned) Executable Blocking
  • Use Case: Prevent execution of binaries from suspicious locations, such as %TEMP% or %APPDATA% directories.
  • Implementation: Block execution of .exe, .bat, or .ps1 files from user-writable directories.
Dynamic Analysis Prevention
  • Use Case: Use behavior-based execution prevention tools to identify and block malicious activity in real time.
  • Implemenation: Employ EDR solutions that analyze runtime behavior and block suspicious code execution.
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Detection Coverage

2/6 layers
Coverage across standard detection surfaces. Rows marked none have no rule of that type mapped. Some are real blind spots worth closing; others are simply not applicable to this technique (e.g. YARA matches malware files, not network behaviour).
Behavioral / log (Sigma) 3
Analytics (MITRE CAR) 2
Runtime / container (Falco) none
File / malware (YARA) none
Network (Suricata/Snort) none
Vuln scan (Nuclei) none
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CAR Analytics

2
MITRE Cyber Analytics Repository - field-tested detection logic for this technique, written as pseudocode/queries you adapt to your own SIEM (Splunk, Sentinel, EQL). Each is a ready starting point for a detection rule, not just a description.
CAR-2013-01-002Moderate coverageAutorun Differences

The Sysinternals tool [Autoruns](../sensors/autoruns) checks the registry and file system for known identify persistence mechanisms. It will output any tools identified, including built-in or added-on Microsoft functionality and third party software. Many of these locations are known by adversaries and used to obtain Persistence.

Running Autoruns periodically in an environment makes it possible to collect and monitor its output for differences, which may include the removal or addition of persistent tools. Depending on the persistence mechanism and location, legitimate software may be more likely to make changes than an adversary tool. Thus, this analytic may result in significant noise in a highly dynamic environment.

While Autoruns is a convenient method to scan for programs using persistence mechanisms its scanning nature does not conform well to streaming based analytics. This analytic could be replaced with one that draws from sensors that collect registry and file information if streaming analytics are desired. Utilizes the Sysinternals autoruns tool (ignoring validated Microsoft entries).

Primarily not a detection analytic by itself but through analysis of results by an analyst can be used for such. Building another analytic on top of this one identifying unusual entries would likely be a beneficial alternative.

CAR-2021-11-002Medium coverageRegistry Edit with Modification of Userinit, Shell or Notify

Detection of modification of the registry key values of Notify, Userinit, and Shell located in HKEY_LOCAL_MACHINE\Software\Microsoft\Windows NT\CurrentVersion\Winlogon\ and HKEY_LOCAL_USER\Software\Microsoft\Windows NT\CurrentVersion\Winlogon\. When a user logs on, the Registry key values of Notify, Userinit and Shell are used to load dedicated Windows component. Attackers may insert malicious payload following the legitimate value to launch a malicious payload.

Pseudocode - Userinit/Shell/Notify Registry Modifications
processes = search Process:create
logon_reg_processes = filter processes where command_line CONTAINS("*\\Microsoft\\Windows NT\\CurrentVersion\\Winlogon*") AND (command_line CONTAINS("*Userinit*") OR command_line CONTAINS("*Shell*") OR command_line CONTAINS("*Notify*")) AND (((command_line CONTAINS("*reg*") OR command_line CONTAINS("*add*") OR command_line CONTAINS("*/d*")) OR (command_line CONTAINS("*Set-ItemProperty*") OR command_line CONTAINS("*New-ItemProperty*") OR command_line CONTAINS("*-value*"))))
reg_keys = search Registry:value_edit
logon_reg_keys = filter reg_keys where (value="Userinit" OR value="Shell" OR value="Notify")
output logon_reg_processes, logon_reg_keys
Splunk - Splunk Search - Modification of Userinit, Shell or Notify
(((((EventCode="4688" OR EventCode="1") ((CommandLine="*reg*" CommandLine="*add*" CommandLine="*/d*") OR ((CommandLine="*Set-ItemProperty*" OR CommandLine="*New-ItemProperty*") CommandLine="*-value*")) CommandLine="*\\Microsoft\\Windows NT\\CurrentVersion\\Winlogon*" (CommandLine="*Userinit*" OR CommandLine="*Shell*" OR CommandLine="*Notify*")) OR ((EventCode="4657") (ObjectValueName="Userinit" OR ObjectValueName="Shell" OR ObjectValueName="Notify"))) OR ((EventCode="13") (TargetObject="*Userinit" OR TargetObject="*Shell" OR TargetObject="*Notify"))))
Elastic - Elastic Search - Modification of Userinit, Shell or Notify
(((EventCode:("4688" OR "1") AND ((process.command_line:*reg* AND process.command_line:*add* AND process.command_line:*\/d*) OR (process.command_line:(*Set\-ItemProperty* OR *New\-ItemProperty*) AND process.command_line:*\-value*)) AND process.command_line:*\\Microsoft\\Windows\ NT\\CurrentVersion\\Winlogon* AND process.command_line:(*Userinit* OR *Shell* OR *Notify*)) OR (EventCode:"4657" AND winlog.event_data.ObjectValueName:("Userinit" OR "Shell" OR "Notify"))) OR (EventCode:"13" AND winlog.event_data.TargetObject:(*Userinit OR *Shell OR *Notify)))
LogPoint - LogPoint Search - Modification of Userinit, Shell or Notify
(((EventCode IN ["4688", "1"] ((CommandLine="*reg*" CommandLine="*add*" CommandLine="*/d*") OR (CommandLine IN ["*Set-ItemProperty*", "*New-ItemProperty*"] CommandLine="*-value*")) CommandLine="*\\Microsoft\\Windows NT\\CurrentVersion\\Winlogon*" CommandLine IN ["*Userinit*", "*Shell*", "*Notify*"]) OR (EventCode IN "4657" ObjectValueName IN ["Userinit", "Shell", "Notify"])) OR (EventCode IN "13" TargetObject IN ["*Userinit", "*Shell", "*Notify"]))
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Comply & Defend

NIST 800-53AC-02, AC-03, AC-05, AC-06, AC-17, CM-05, CM-07, IA-02, SI-04, SI-07, SI-10, SI-14, SI-16
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