第13节第二种shellcode编写实战(2)

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一、C语言方式编写shellcode

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0x60PPEB lpPeb = (PPEB)__readgsqword(0x60);
#else            // 32位PEB偏移为0x30PPEB lpPeb = (PPEB)__readfsdword(0x30);
#endifPLIST_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：