在第二种shellcode编写实战(1)的基础上，新增加一个CAPI类，将所有用到的函数都在这个类中做动态调用的处理，这样使得整个shellcode功能结构更加清晰。
1. 新建类CAPI（即api.h和api.cpp两个文件）：
api.h：
#pragma once
#include <windows.h>
#include <Winternl.h>
class CAPI
{
private:
HMODULE GetKernel32BaseAddress();
FARPROC _GetPorcAddress();
public:
void InitFunctions();
public:
typedef HANDLE(WINAPI* FN_CreateFileA)(
_In_ LPCSTR lpFileName,
_In_ DWORD dwDesiredAccess,
_In_ DWORD dwShareMode,
_In_opt_ LPSECURITY_ATTRIBUTES lpSecurityAttributes,
_In_ DWORD dwCreationDisposition,
_In_ DWORD dwFlagsAndAttributes,
_In_opt_ HANDLE hTemplateFile);
typedef int (WINAPI* FN_MessageBoxA)(
__in_opt HWND hWnd,
__in_opt LPCSTR lpText,
__in_opt LPCSTR lpCaption,
__in UINT uType);
typedef HMODULE(WINAPI* FN_LoadLibraryA)(
__in LPCSTR lpLibFileName);
public:
FN_CreateFileA CreateFileA;
FN_MessageBoxA MessageBoxA;
FN_LoadLibraryA LoadLibraryA;
};api.cpp：
#include "api.h"
// 获取kernel32基址
HMODULE CAPI::GetKernel32BaseAddress()
{
HMODULE hKernel32 = NULL;
// 用户保存模块名
WCHAR wszModuleName[MAX_PATH];
#ifdef _WIN64 // 64位PEB偏移为0x60
PPEB lpPeb = (PPEB)__readgsqword(0x60);
#else // 32位PEB偏移为0x30
PPEB lpPeb = (PPEB)__readfsdword(0x30);
#endif
PLIST_ENTRY pListHead = &lpPeb->Ldr->InMemoryOrderModuleList;
PLIST_ENTRY pListData = pListHead->Flink;
// 遍历所有模块
while (pListData != pListHead)
{
PLDR_DATA_TABLE_ENTRY pLDRData = CONTAINING_RECORD(pListData, LDR_DATA_TABLE_ENTRY, InMemoryOrderLinks);
DWORD dwLen = pLDRData->FullDllName.Length / 2;
if (dwLen > 12) // 12 是"kernel32.dll"的长度，获取到的完整路径肯定要比模块名长
{
// 从获取到的模块完整路径中提取模块名
for (size_t i = 0; i < 12; i++)
{
wszModuleName[11 - i] = pLDRData->FullDllName.Buffer[dwLen - 1 - i];
}
// 最终要获取的目标模块名（"kernel32.dll"），逐个字节比较，包含大小写。
if ((wszModuleName[0] == 'k' || wszModuleName[0] == 'K') &&
(wszModuleName[1] == 'e' || wszModuleName[1] == 'E') &&
(wszModuleName[2] == 'r' || wszModuleName[2] == 'R') &&
(wszModuleName[3] == 'n' || wszModuleName[3] == 'N') &&
(wszModuleName[4] == 'e' || wszModuleName[4] == 'E') &&
(wszModuleName[5] == 'l' || wszModuleName[5] == 'L') &&
(wszModuleName[6] == '3') &&
(wszModuleName[7] == '2') &&
(wszModuleName[8] == '.') &&
(wszModuleName[9] == 'd' || wszModuleName[9] == 'D') &&
(wszModuleName[10] == 'l' || wszModuleName[10] == 'L') &&
(wszModuleName[11] == 'l' || wszModuleName[11] == 'L'))
{
hKernel32 = (HMODULE)pLDRData->DllBase;
break;
}
}
pListData = pListData->Flink;
}
return hKernel32;
}
// 获取GetPorcAddress函数地址
FARPROC CAPI::_GetPorcAddress()
{
// 保存最终结果
FARPROC pGetPorcAddress = NULL;
// kernel32基址
HMODULE hKernel32 = GetKernel32BaseAddress();
if (!hKernel32)
{
return NULL;
}
PIMAGE_DOS_HEADER lpDosHeader = (PIMAGE_DOS_HEADER)hKernel32;
PIMAGE_NT_HEADERS lpNTHeader = (PIMAGE_NT_HEADERS)((unsigned char*)hKernel32 + lpDosHeader->e_lfanew);
// 模块有效性验证
if (!lpNTHeader->OptionalHeader.DataDirectory[IMAGE_DIRECTORY_ENTRY_EXPORT].Size)
{
return NULL;
}
if (!lpNTHeader->OptionalHeader.DataDirectory[IMAGE_DIRECTORY_ENTRY_EXPORT].VirtualAddress)
{
return NULL;
}
// 通过导出表中的导出函数名，定位"GetProcAddress"的位置
PIMAGE_EXPORT_DIRECTORY lpExports = (PIMAGE_EXPORT_DIRECTORY)((unsigned char*)hKernel32 + lpNTHeader->OptionalHeader.DataDirectory[IMAGE_DIRECTORY_ENTRY_EXPORT].VirtualAddress);
PDWORD lpdwFunName = (PDWORD)((unsigned char*)hKernel32 + lpExports->AddressOfNames);
PWORD lpdwOrd = (PWORD)((unsigned char*)hKernel32 + lpExports->AddressOfNameOrdinals);
PDWORD lpdwFunAddr = (PDWORD)((unsigned char*)hKernel32 + lpExports->AddressOfFunctions);
for (DWORD dwLoop = 0; dwLoop <= lpExports->NumberOfNames - 1; dwLoop++)
{
char* pFunName = (char*)(lpdwFunName[dwLoop] + (unsigned char*)hKernel32);
// 比较函数名
if (
pFunName[0] == 'G' &&
pFunName[1] == 'e' &&
pFunName[2] == 't' &&
pFunName[3] == 'P' &&
pFunName[4] == 'r' &&
pFunName[5] == 'o' &&
pFunName[6] == 'c' &&
pFunName[7] == 'A' &&
pFunName[8] == 'd' &&
pFunName[9] == 'd' &&
pFunName[10] == 'r' &&
pFunName[11] == 'e' &&
pFunName[12] == 's' &&
pFunName[13] == 's'
)
{
pGetPorcAddress = (FARPROC)(lpdwFunAddr[lpdwOrd[dwLoop]] + (unsigned char*)hKernel32);
break;
}
}
return pGetPorcAddress;
}
// 初始化所有用到的函数
void CAPI::InitFunctions()
{
// 获取GetPorcAddress函数地址
typedef FARPROC(WINAPI* FN_GetProcAddress)(__in HMODULE hModule, __in LPCSTR lpProcName);
FN_GetProcAddress fn_GetProcAddress = (FN_GetProcAddress)_GetPorcAddress();
if (fn_GetProcAddress)
{
// 获取LoadLibraryA函数地址
char szLoadLibraryA[] = { 'L','o','a','d','L','i','b','r','a','r','y','A',0 };
LoadLibraryA = (FN_LoadLibraryA)fn_GetProcAddress(GetKernel32BaseAddress(), szLoadLibraryA);
if (LoadLibraryA)
{
// 获取MessageBoxA函数地址
char szUser32[] = { 'U','s','e','r','3','2','.','d','l','l',0 };
char szMessageBoxA[] = { 'M','e','s','s','a','g','e','B','o','x','A',0 };
MessageBoxA = (FN_MessageBoxA)fn_GetProcAddress(LoadLibraryA(szUser32), szMessageBoxA);
// 获取CreateFileA函数地址
char szCreateFileA[] = { 'C','r','e','a','t','e','F','i','l','e','A',0 };
CreateFileA = (FN_CreateFileA)fn_GetProcAddress(GetKernel32BaseAddress(), szCreateFileA);
}
}
}2. 在CAPI中，使用InitFunctions函数来初始化所有shellcode中用到的函数，在shellcode执行功能处，进行如下调用即可（a.start.cpp）：
#include "a.start.h"
#include "shellcode.h"
#include "api.h"
void ShellCodeStart()
{
CAPI api;
// 初始化所有用到的函数
api.InitFunctions();
CDoShellcode shellcode;
// 创建文件
shellcode.DoCreateFile(&api);
// 弹框提示
shellcode.DoMessageBox(&api);
// 其他功能...
}3. 在类CDoShellcode中，将所有函数功能执行的参数都传递一个CAPI的指针变量，那么所有功能都可以使用CAPI中的函数。比如CDoShellcode中的DoCreateFile方法：
// 功能：创建文件 D:\1.txt
int CDoShellcode::DoCreateFile(CAPI* api)
{
// 执行动态CreateFileA，创建文件
char szFilePath[] = { 'D',':','\\','1','.','t','x','t',0 };
api->CreateFileA(szFilePath, GENERIC_WRITE, 0, NULL, CREATE_ALWAYS, 0, NULL);
return 0;
}如此一来，对类CDoShellcode而言，我们只关注功能的实现，不必再顾及函数动态调用的问题。所有用到的动态函数的实现都可以共享CAPI中的实现。
项目结构：
两个类：
- CDoShellcode（shellcode.h和shellcode.cpp）：shellcode执行的各类功能；
- CAPI（api.h和api.cpp）：所有shellcode使用到的动态函数。
