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Basically, I cannot find which process is being written to when WriteProcessMemory is being called. Currently I'm Setting Breakpoints on WriteProcessMemory and OpenProcess. However, the process handle being passed to WriteProcessMemory is different from that obtained from OpenProcess, so it appears that the process handle is being obtained in another way. Is there something I'm missing out on? Should I add more breakpoints on other functions?

4

It is also easy using x64dbg. When you break on the WriteProcessMemory the handle will be at [esp+0x4] in the memory.

Image of stack view in x64dbg

After you write down the handle (in this case 0xDC) you may go to the Handles tab in the x64dbg main window, then Right click -> Refresh. All the handles associated with your debugged process will be listed. Now you need to find the corresponding handle and thats it.

Image of handles tab in x64dbg

As you can see, in my case the WriteProcessMemory was writting to process with PID 0x7A30.

If you don't use debugger that can list handles (unlikely) you can use external tool like Process Explorer, which also has the ability to list all process associated handles.

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3

which debugger are you using ?
most debuggers will decipher the handle on the spot
that is you can find out the handle info when you have broken on the WriteProcessMemory() Call itself

here is how you can do it with windbg
i am debugging ollydbg and olllydbg ais debugging calc.exe
ollydbg is setting a breakpoint in calc.exe (uses WriteProcessMemory() )

0:000> bl
     0 e Disable Clear  752444cf     0001 (0001)  0:**** KERNELBASE!WriteProcessMemory

0:000> .lastevent
Last event: c90.e10: Hit breakpoint 0

0:000> kb1
 # ChildEBP RetAddr  Args to Child              
00 0012bd44 00457929 0000014c 009c2000 02973020 KERNELBASE!WriteProcessMemory

0:000> !handle 14c f
Handle 14c
  Type          Process
  Attributes    0
  GrantedAccess 0x1fffff:
         Delete,ReadControl,xxxx,SetPort
  HandleCount   4
  PointerCount  10
  Name          <none>
  Object Specific Information
    Process Id  3336
    Parent Process  3216
    Base Priority 8

0:000> dx Debugger.Utility.Control.ExecuteCommand(".tlist").Where(a=>a.Contains("3336")==true)
Debugger.Utility.Control.ExecuteCommand(".tlist").Where(a=>a.Contains("3336")==true)                
    [0x30]           :  0n3336 calc.exe

0:000> dx Debugger.Utility.Control.ExecuteCommand(".tlist").Where(a=>a.Contains("3216")==true)
Debugger.Utility.Control.ExecuteCommand(".tlist").Where(a=>a.Contains("3216")==true)                
    [0x2f]           :  0n3216 ollydbg.exe
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2

Many programs, especially malware, start a suspended child process (CreateProcess variants), overwrite its code with their own (WriteProcessMemory with or without VirtualAllocEx) and resume the main thread (ResumeThread).

Also look for ReadProcessMemory, it is possible that the call to OpenProcess that you see is actually the same process reading from its own pages and the WriteProcessMemory is writing to the newly created process, with its different handle.

Note that these functions also have low-level variants (ZwCreateThread etc.)

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