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ATT&CK Technique

AppInit DLLs

T1546.010 · privilege-escalation, persistence

Adversaries may establish persistence and/or elevate privileges by executing malicious content triggered by AppInit DLLs loaded into processes. Dynamic-link libraries (DLLs) that are specified in the AppInit_DLLs value in the Registry keys HKEY_LOCAL_MACHINE\Software\Microsoft\Windows NT\CurrentVersion\Windows or HKEY_LOCAL_MACHINE\Software\Wow6432Node\Microsoft\Windows NT\CurrentVersion\Windows are loaded by user32.dll into every process that loads user32.dll. In practice this is nearly every program, since user32.dll is a very common library.

Similar to Process Injection, these values can be abused to obtain elevated privileges by causing a malicious DLL to be loaded and run in the context of separate processes on the computer. Malicious AppInit DLLs may also provide persistence by continuously being triggered by API activity. The AppInit DLL functionality is disabled in Windows 8 and later versions when secure boot is enabled.

Windows
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Actors Using This

1
us_israel_joint_offensive_cyberStuxnet
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Atomic Tests

1
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.
command_promptelevatedwindowsInstall AppInit Shim
AppInit_DLLs is a mechanism that allows an arbitrary list of DLLs to be loaded into each user mode process on the system. Upon succesfully execution, you will see the message "The operation completed successfully." Each time the DLL is loaded, you will see a message box with a message of "Install AppInit Shim DLL was called!" appear. This will happen regularly as your computer starts up various applications and may in fact drive you crazy. A reliable way to make the message box appear and verify the AppInit Dlls are loading is to start the notepad application. Be sure to run the cleanup commands afterwards so you don't keep getting message boxes showing up. Note: If secure boot is enabled, this technique will not work. https://docs.microsoft.com/en-us/windows/win32/dlls/secure-boot-and-appinit-dlls 
reg.exe import "#{registry_file}"
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Mitigations

2
MITRE ATT&CK mitigations - vendor-agnostic guidance for reducing exposure to this technique.
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.
M1051Update Software

Software updates ensure systems are protected against known vulnerabilities by applying patches and upgrades provided by vendors. Regular updates reduce the attack surface and prevent adversaries from exploiting known security gaps. This includes patching operating systems, applications, drivers, and firmware.

Regular Operating System Updates
  • Implementation: Apply the latest Windows security updates monthly using WSUS (Windows Server Update Services) or a similar patch management solution. Configure systems to check for updates automatically and schedule reboots during maintenance windows.
  • Use Case: Prevents exploitation of OS vulnerabilities such as privilege escalation or remote code execution. Application Patching.
  • Implementation: Monitor Apache's update release notes for security patches addressing vulnerabilities. Schedule updates for off-peak hours to avoid downtime while maintaining security compliance.
  • Use Case: Prevents exploitation of web application vulnerabilities, such as those leading to unauthorized access or data breaches. Firmware Updates.
  • Implementation: Regularly check the vendor’s website for firmware updates addressing vulnerabilities. Plan for update deployment during scheduled maintenance to minimize business disruption.
  • Use Case: Protects against vulnerabilities that adversaries could exploit to gain access to network devices or inject malicious traffic. Emergency Patch Deployment.
  • Implementation: Use the emergency patch deployment feature of the organization's patch management tool to apply updates to all affected Exchange servers within 24 hours.
  • Use Case: Reduces the risk of exploitation by rapidly addressing critical vulnerabilities. Centralized Patch Management.
  • Implementation: Implement a centralized patch management system, such as SCCM or ManageEngine, to automate and track patch deployment across all environments. Generate regular compliance reports to ensure all systems are updated.
  • Use Case: Streamlines patching processes and ensures no critical systems are missed.
Tools for Implementation Patch Management Tools
  • WSUS: Manage and deploy Microsoft updates across the organization.
  • ManageEngine Patch Manager Plus: Automate patch deployment for OS and third-party apps.
  • Ansible: Automate updates across multiple platforms, including Linux and Windows.
Vulnerability Scanning Tools
  • OpenVAS: Open-source vulnerability scanning to identify missing patches.
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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) 1
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-2020-09-005Moderate coverageAppInit DLLs

Adversaries may establish persistence and/or elevate privileges by executing malicious content triggered by AppInit DLLs loaded into processes. Dynamic-link libraries (DLLs) that are specified in the AppInit_DLLs value in the Registry keys HKEY_LOCAL_MACHINE\Software\Microsoft\Windows NT\CurrentVersion\Windows or HKEY_LOCAL_MACHINE\Software\Wow6432Node\Microsoft\Windows NT\CurrentVersion\Windows are loaded by user32.dll into every process that loads user32.dll. These values can be abused to obtain elevated privileges by causing a malicious DLL to be loaded and run in the context of separate processes.

Accordingly, this analytic looks for modifications to these registry keys that may be indicative of this type of abuse.

Pseudocode - Pseudocode - AppInit DLL registry modification
registry_keys = search (Registry:Create AND Registry:Remove AND Registry:Edit)
appinit_keys = filter registry_keys where (
  key = "*\SOFTWARE\Microsoft\Windows NT\CurrentVersion\Windows\Appinit_Dlls\*" OR
  key = "*\SOFTWARE\\Wow6432Node\Microsoft\Windows NT\CurrentVersion\Windows\Appinit_Dlls\*""
  )
output clsid_keys
Splunk - Splunk search - AppInit DLL registry modification
index=__your_sysmon_index__ (EventCode=12 OR EventCode=13 OR EventCode=14) (TargetObject="*\\SOFTWARE\\Microsoft\\Windows NT\\CurrentVersion\\Windows\\Appinit_Dlls\\*" OR TargetObject="*\\SOFTWARE\\Wow6432Node\\Microsoft\\Windows NT\\CurrentVersion\\Windows\\Appinit_Dlls\\*")
LogPoint - LogPoint search - AppInit DLL registry modification
norm_id=WindowsSysmon event_id IN [12, 13, 14] target_object IN ["*\SOFTWARE\Microsoft\Windows NT\CurrentVersion\Windows\Appinit_Dlls\*", "*\SOFTWARE\Wow6432Node\Microsoft\Windows NT\CurrentVersion\Windows\Appinit_Dlls\*"]
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Comply & Defend

NIST 800-53CM-02, CM-07, SI-02, SI-07, SI-10
D3FEND12 defensive techniques
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