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T1546.010 - AppInit DLLs

T1546.010 - AppInit 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. In practice this is nearly every program, since user32.dll is a very common library. (Citation: Elastic Process Injection July 2017)

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. (Citation: AppInit Registry) 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. (Citation: AppInit Secure Boot)

Atomic Tests#

Atomic Test #1 - Install 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

Supported Platforms: windows

Elevation Required (e.g. root or admin)

Dependencies: Run with powershell!#

Description: Reg files must exist on disk at specified locations (#{registry_file} and #{registry_cleanup_file})#
Check Prereq Commands:#
if ((Test-Path "PathToAtomicsFolder\T1546.010\src\T1546.010.reg") -and (Test-Path "PathToAtomicsFolder\T1546.010\src\T1546.010-cleanup.reg")) {exit 0} else {exit 1}
Get Prereq Commands:#
[Net.ServicePointManager]::SecurityProtocol = [Net.SecurityProtocolType]::Tls12
New-Item -Type Directory (split-path "PathToAtomicsFolder\T1546.010\src\T1546.010.reg") -ErrorAction ignore | Out-Null
Invoke-WebRequest "https://github.com/redcanaryco/atomic-red-team/raw/master/atomics/T1546.010/src/T1546.010.reg" -OutFile "PathToAtomicsFolder\T1546.010\src\T1546.010.reg"
Invoke-WebRequest "https://github.com/redcanaryco/atomic-red-team/raw/master/atomics/T1546.010/src/T1546.010-cleanup.reg" -OutFile "PathToAtomicsFolder\T1546.010\src\T1546.010-cleanup.reg"
Description: DLL’s must exist in the C:\Tools directory (T1546.010.dll and T1546.010x86.dll)#
Check Prereq Commands:#
if ((Test-Path c:\Tools\T1546.010.dll) -and (Test-Path c:\Tools\T1546.010x86.dll)) {exit 0} else {exit 1}
Get Prereq Commands:#
New-Item -Type Directory C:\Tools -ErrorAction ignore | Out-Null
Invoke-WebRequest "https://github.com/redcanaryco/atomic-red-team/raw/master/atomics/T1546.010/bin/T1546.010.dll" -OutFile C:\Tools\T1546.010.dll
Invoke-WebRequest "https://github.com/redcanaryco/atomic-red-team/raw/master/atomics/T1546.010/bin/T1546.010x86.dll" -OutFile C:\Tools\T1546.010x86.dll


Invoke-AtomicTest T1546.010 -TestNumbers 1 -GetPreReqs

Attack Commands: Run with command_prompt#

reg.exe import "PathToAtomicsFolder\T1546.010\src\T1546.010.reg"

Invoke-AtomicTest T1546.010 -TestNumbers 1

Cleanup:#

reg.exe import "PathToAtomicsFolder\T1546.010\src\T1546.010-cleanup.reg" >nul 2>&1

Invoke-AtomicTest T1546.010 -TestNumbers 1 -Cleanup

Detection#

Monitor DLL loads by processes that load user32.dll and look for DLLs that are not recognized or not normally loaded into a process. Monitor the AppInit_DLLs Registry values for modifications that do not correlate with known software, patch cycles, etc. Monitor and analyze application programming interface (API) calls that are indicative of Registry edits such as RegCreateKeyEx and RegSetValueEx. (Citation: Elastic Process Injection July 2017)

Tools such as Sysinternals Autoruns may also be used to detect system changes that could be attempts at persistence, including listing current AppInit DLLs. (Citation: TechNet Autoruns)

Look for abnormal process behavior that may be due to a process loading a malicious DLL. Data and events should not be viewed in isolation, but as part of a chain of behavior that could lead to other activities, such as making network connections for Command and Control, learning details about the environment through Discovery, and conducting Lateral Movement.

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