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Introduction In the complex ecosystem of Windows cryptography, numerous undocumented or under-documented functions reside within system DLLs, serving specific purposes for certificate management, enrollment, and validation. One such intriguing function is CryptExtAddCERMachineOnlyAndHwnd located in cryptext.dll .

if (pFunc) HRESULT hr = pFunc(GetDesktopWindow(), 0x00000001, L"C:\\corp-root.cer", 0); if (SUCCEEDED(hr)) MessageBoxW(NULL, L"Certificate installed to Local Machine store", L"Success", MB_OK);

#include <windows.h> #include <cryptext.h> // Not officially available – declare manually // Declare function pointer from cryptext.dll typedef HRESULT (WINAPI *pCryptExtAddCERMachineOnlyAndHwnd)( HWND hwnd, DWORD dwFlags, LPCWSTR wszFilePath, DWORD dwReserved );

HRESULT CryptExtAddCERMachineOnlyAndHwnd( HWND hWndParent, DWORD dwFlags, LPCWSTR wszFileName, // possibly additional parameters ); A more precise reconstruction from binary analysis (e.g., using IDA Pro or Ghidra on cryptext.dll from Windows 7 or Server 2008 R2) suggests:

However, its undocumented nature, strict privilege requirements, and potential for misuse make it unsuitable for production software today. Developers encountering this function should consider migrating to documented alternatives ( CertAddCertificateContextToStore with CERT_SYSTEM_STORE_LOCAL_MACHINE ). Security researchers should recognize this function as a common vector for persistent certificate-based backdoors and monitor its invocation in system audits.

pCryptExtAddCERMachineOnlyAndHwnd pFunc = (pCryptExtAddCERMachineOnlyAndHwnd) GetProcAddress(hMod, "CryptExtAddCERMachineOnlyAndHwnd");

certmgr.dll!OnAddCertificate() cryptext.dll!CryptExtAddCERMachineOnlyAndHwnd() crypt32.dll!CertAddCertificateLinkToStore() Assuming you have a valid certificate file C:\certs\corp-root.cer and an elevated process with a window handle, you might use this function as follows (pseudo-code based on reverse engineering):