Stealing Program's Memory

Cory Nelson

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2 Dec 20032 min read

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An advanced article on allocating and using memory in another process using the Win32 API.

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Introduction

I was recently trying to steal strings from another program's listview control. You need to pass a pointer so it knows where to put the string. Normally, this wouldn't be a problem, but because Windows uses virtual memory, pointers are not valid across programs.

Virtual memory is how Windows deals out memory to all its programs. It makes programs think they have 2 Gb of memory to use. It also protects programs from using each other's memory so if one program crashes, it doesn't take down the whole system with it.

So after coding a fair bit, I realized my pointers were all invalid and it wouldn't work. A few hours of digging through MSDN brought me to the functions VirtualAllocEx(), VirtualFreeEx(), WriteProcessMemory() and ReadProcessMemory(). Armed with this new information, I set out to modify my code. Here is what I had so far:

#define WIN32_LEAN_AND_MEAN
#include <stdio.h>
#include <windows.h>
#include <commctrl.h>

int main(void) {
 /* Run through the windows until we find our listview. */
 HWND hwnd=FindWindow(NULL, "Stealing Program's Memory: ListView");
 HWND listview=FindWindowEx(hwnd, NULL, "SysListView32", NULL);

 int count=(int)SendMessage(listview, LVM_GETITEMCOUNT, 0, 0);
 int i;

 char item[512], subitem[512];

 /* Shove all items of listview into item and subitem
    and print out one by one. */

 LVITEM lvi;
 lvi.cchTextMax=512;

 for(i=0; i<count; i++) {
  lvi.iSubItem=0;
  lvi.pszText=item;
  SendMessage(listview, LVM_GETITEMTEXT, (WPARAM)i, (LPARAM)&lvi);

  lvi.iSubItem=1;
  lvi.pszText=subitem;
  SendMessage(listview, LVM_GETITEMTEXT, (WPARAM)i, (LPARAM)&lvi);

  printf("%s - %s\n", item, subitem);
 }
 return 0;
}

As I said before, this won't work. The pointers to lvi, item, and subitem all get screwed when they go across process. The solution? Use WriteProcessMemory() and ReadProcessMemory() to use the other programs memory, perform LVM_GETITEMTEXT on it, and read it back. Hackish yes, but then again reading items from another program's listview control is one giant hack.

First, we get the process of the listview like this:

unsigned long pid;
HANDLE process;
GetWindowThreadProcessId(listview, &pid);
process=OpenProcess(PROCESS_VM_OPERATION|PROCESS_VM_READ|
                    PROCESS_VM_WRITE|PROCESS_QUERY_INFORMATION, FALSE, pid);

Next, we create three pointers, LVITEM *_lvi, char *_item, and char *_subitem and allocate them in the other program's virtual memory space with VirtualAllocEx():

LVITEM *_lvi=(LVITEM*)VirtualAllocEx(process, NULL, sizeof(LVITEM),
                                     MEM_COMMIT, PAGE_READWRITE);
char *_item=(char*)VirtualAllocEx(process, NULL, 512, MEM_COMMIT,
                                  PAGE_READWRITE);
char *_subitem=(char*)VirtualAllocEx(process, NULL, 512, MEM_COMMIT,
                                     PAGE_READWRITE);

Now, we point lvi.pszText to _item, and copy its memory to _lvi using WriteMemoryProcess():

lvi.pszText=_item;
WriteProcessMemory(process, _lvi, &lvi, sizeof(LVITEM), NULL);

Now that we have an LVITEM pointer that is valid in the other programs virtual memory, we can shoot off LVM_GETITEMTEXT to listview and copy _item's text into item so we can read it in our program:

SendMessage(hwnd, LVM_GETITEMTEXT, (WPARAM)i, (LPARAM)_lvi);
ReadProcessMemory(process, _item, item, max, NULL);

Repeat that for subitem, then free the memory we used in the other program's memory:

VirtualFreeEx(process, _lvi, 0, MEM_RELEASE);
VirtualFreeEx(process, _item, 0, MEM_RELEASE);
VirtualFreeEx(process, _subitem, 0, MEM_RELEASE);

Yay, all done. In case that didn't make too much sense to you, here is our new code, all fixed up:

#define WIN32_LEAN_AND_MEAN
#include <stdio.h>
#include <windows.h>
#include <commctrl.h>

int main(void) {
 HWND hwnd=FindWindow(NULL, "Stealing Program's Memory: ListView");
 HWND listview=FindWindowEx(hwnd, NULL, "SysListView32", NULL);

 int count=(int)SendMessage(listview, LVM_GETITEMCOUNT, 0, 0);
 int i;

 LVITEM lvi, *_lvi;
 char item[512], subitem[512];
 char *_item, *_subitem;
 unsigned long pid;
 HANDLE process;

 GetWindowThreadProcessId(listview, &pid);
 process=OpenProcess(PROCESS_VM_OPERATION|PROCESS_VM_READ|
                     PROCESS_VM_WRITE|PROCESS_QUERY_INFORMATION, FALSE, pid);

 _lvi=(LVITEM*)VirtualAllocEx(process, NULL, sizeof(LVITEM),
                              MEM_COMMIT, PAGE_READWRITE);
 _item=(char*)VirtualAllocEx(process, NULL, 512, MEM_COMMIT,
                             PAGE_READWRITE);
 _subitem=(char*)VirtualAllocEx(process, NULL, 512, MEM_COMMIT,
                                PAGE_READWRITE);

 lvi.cchTextMax=512;

 for(i=0; i<count; i++) {
  lvi.iSubItem=0;
  lvi.pszText=_item;
  WriteProcessMemory(process, _lvi, &lvi, sizeof(LVITEM), NULL);
  SendMessage(listview, LVM_GETITEMTEXT, (WPARAM)i, (LPARAM)_lvi);

  lvi.iSubItem=1;
  lvi.pszText=_subitem;
  WriteProcessMemory(process, _lvi, &lvi, sizeof(LVITEM), NULL);
  SendMessage(listview, LVM_GETITEMTEXT, (WPARAM)i, (LPARAM)_lvi);

  ReadProcessMemory(process, _item, item, 512, NULL);
  ReadProcessMemory(process, _subitem, subitem, 512, NULL);

  printf("%s - %s\n", item, subitem);
 }

 VirtualFreeEx(process, _lvi, 0, MEM_RELEASE);
 VirtualFreeEx(process, _item, 0, MEM_RELEASE);
 VirtualFreeEx(process, _subitem, 0, MEM_RELEASE);

 return 0;
}

If you're looking to use a program's memory for another reason, or have had a similar problem to mine, adapting this should be fairly easy.

This article was originally written for int64.org.

License

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Written By

Cory Nelson

Web Developer

United States

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Stealing Program's Memory

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