是一段可注入的指令(opcode),可以在被攻击的程序内运行。
短小精悍,灵活多变,独立存在,无需任何文件格式的包装,因为shellcode直接操作寄存器和函数,所以opcode必须是16进制形式。因此也不能用高级语言编写shellcode。在内存中运行,无需运行在固定的宿主进程上。
将shellcode注入缓冲区,然后欺骗目标程序执行它。而将shellcode注入缓冲区最常用的方法是利用目标系统上的缓冲区溢出漏洞。
关闭VS自动优化没有使用到的变量
自定义函数入口
GetProAddress 从dll中获取函数的地址
参数1:调用dll的句柄,参数2:函数名
Bug:error C2760: 语法错误: 意外的令牌“标识符”,预期的令牌为“类型说明符”
打开项目工程-> 属性 -> c/c++ --> 语言 -> 符合模式 修改成否即可 如果这样设置将无法使用c函数。
这个比较关键,否则使用printf就直接崩溃或者是编译报错
最佳方案是:修改平台工具集
因为vs会将全局变量编译在其他区段中 结果就是一个绝对的地址不能使用static定义变量(变量放到内部函数使用)
如下:
属性->常规->平台工具集 选择xp版本
C/C++->代码生成->运行库选择MT
安全检查禁用
链接器->高级->入口点修改为EntryMain
在编写shellcode时,所有用到的函数都需要动态调用,通过LoadLibrary函数加载动态链接库,GetProAddress获取动态链接库中函数的地址。所以获取到GetProAddress和LoadLibrary地址时非常重要的。通过GetProAddress和LoadLibrary,可以获取到已加载的动态链接库的地址。
动态获取Kernel32.dll基址和GetProAddress 地址
在正常情况下,我们不知道LoadLibraryA的地址,所以不能直接使用该函数。GetProAddress是动态链接库Kernel32.dll中的函数。每个进程内部加载都会加载Kernel32.dll,获取到加载Kernel32.dll地址就可以获取到GetProAddress函数的地址。通过汇编内嵌获取到Kernel32的基址。获取到GetProAddress地址后,就可以获取到所有需要的函数的地址。
pE文件运行时加载的链接库
代码如下:
#include <windows.h>#include <stdio.h>//内嵌汇编获取Kernel32的地址__declspec(naked) DWORD getKernel32(){ __asm { mov eax,fs:[30h] mov eax,[eax+0ch] mov eax,[eax+14h] mov eax,[eax] mov eax,[eax] mov eax,[eax+10h] ret }}//通过kernel32基址获取GetProcAddress的地址FARPROC _GetProcAddress(HMODULE hModuleBase) { PIMAGE_DOS_HEADER lpDosHeader = (PIMAGE_DOS_HEADER)hModuleBase; PIMAGE_NT_HEADERS32 lpNtHeader = (PIMAGE_NT_HEADERS)((DWORD)hModuleBase + lpDosHeader->e_lfanew); if (!lpNtHeader->OptionalHeader.DataDirectory[IMAGE_DIRECTORY_ENTRY_EXPORT].Size){ return NULL; } if (!lpNtHeader->OptionalHeader.DataDirectory[IMAGE_DIRECTORY_ENTRY_EXPORT].VirtualAddress) { return NULL; } PIMAGE_EXPORT_DIRECTORY lpExports = (PIMAGE_EXPORT_DIRECTORY)((DWORD)hModuleBase + (DWORD)lpNtHeader->OptionalHeader.DataDirectory[IMAGE_DIRECTORY_ENTRY_EXPORT].VirtualAddress); PDWORD lpdwFunName = (PDWORD)((DWORD)hModuleBase + (DWORD)lpExports->AddressOfNames); PWORD lpword = (PWORD)((DWORD)hModuleBase + (DWORD)lpExports->AddressOfNameOrdinals); PDWORD lpdwFunAddr = (PDWORD)((DWORD)hModuleBase + (DWORD)lpExports->AddressOfFunctions); DWORD dwLoop = 0; FARPROC pRet = NULL; for (; dwLoop <= lpExports->NumberOfNames - 1; dwLoop++) { char* pFunName = (char*)(lpdwFunName[dwLoop] + (DWORD)hModuleBase); 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') { pRet = (FARPROC)(lpdwFunAddr[lpword[dwLoop]] + (DWORD)hModuleBase); break; } } return pRet;}int main(){ //kernel32.dll 基址的动态获取 HMODULE hLoadLibrary = LoadLibraryA("kernel32.dll"); //使用内嵌汇编来获取基址 HMODULE _hLoadLibrary = (HMODULE)getKernel32(); //效果是一样的 printf("LoadLibraryA动态获取的地址: 0x%x\n", hLoadLibrary); printf("内嵌汇编获取的地址: 0x%x\n", _hLoadLibrary); //声明定义,先转到到原函数定义,然后重新定义 typedef FARPROC(WINAPI *FN_GetProcAddress)( _In_ HMODULE hModule, _In_ LPCSTR lpProcName ); FN_GetProcAddress fn_GetProcAddress; fn_GetProcAddress = (FN_GetProcAddress)_GetProcAddress(_hLoadLibrary); printf("动态获取GetProcAddress地址: 0x%x\n",fn_GetProcAddress); printf("内置函数获取: 0x%x\n",GetProcAddress);}
可以看到,动态获取的地址和系统函数获取的是一致的
引用前面kernel32.dll和GetProcaddress的获取地址。对于每一个要引用的函数,通过查看定义来声明定义函数,通过GetProcaddress动态获取地址。
具体代码如下:
原C代码:
#include <windows.h>#include <stdio.h>#include <windows.h>int EntryMain(){CreateFileA(“1.txt”, GENERIC_WRITE, 0, NULL, CREATE_ALWAYS, 0, NULL);MessageBoxA(NULL, “hello world”, tip, MB_OK);return 0;}
Shellcode编写:
#include <windows.h>#include <stdio.h>FARPROC getProcAddress(HMODULE hModuleBase);DWORD getKernel32();int EntryMain(){ //声明定义GetProcAddress typedef FARPROC(WINAPI *FN_GetProcAddress)( _In_ HMODULE hModule, _In_ LPCSTR lpProcName ); //获取GetProcAddress真实地址 FN_GetProcAddress fn_GetProcAddress = (FN_GetProcAddress)getProcAddress((HMODULE)getKernel32()); //声明定义CreateFileA 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 ); //将来的替换,地址全部动态获取 //FN_CreateFileA fn_CreateFileA = (FN_CreateFileA)GetProcAddress(LoadLibrary("kernel32.dll"), "CreateFileA"); //带引号的字符串打散处理 char xyCreateFile[] = { 'C','r','e','a','t','e','F','i','l','e','A',0 }; //动态获取CreateFile的地址 FN_CreateFileA fn_CreateFileA = (FN_CreateFileA)fn_GetProcAddress((HMODULE)getKernel32(), xyCreateFile); char xyNewFile[] = { '1','.','t','x','t','\0'}; fn_CreateFileA(xyNewFile, GENERIC_WRITE, 0, NULL, CREATE_ALWAYS, 0, NULL); //定义LoadLibraryA typedef HMODULE(WINAPI *FN_LoadLibraryA)( __in LPCSTR lpLibFileName ); char xyLoadLibraryA[] = { 'L','o','a','d','L','i','b','r','a','r','y','A',0}; //动态获取LoadLibraryA的地址 FN_LoadLibraryA fn_LoadLibraryA = (FN_LoadLibraryA)fn_GetProcAddress((HMODULE)getKernel32(), xyLoadLibraryA); //定义MessageBoxA typedef int (WINAPI *FN_MessageBoxA)( __in_opt HWND hWnd, __in_opt LPCSTR lpText, __in_opt LPCSTR lpCaption, __in UINT uType); //原来的:MessageBoxA(NULL, "Hello world", "tip", MB_OK); char xy_user32[] = { 'u','s','e','r','3','2','.','d','l','l',0 }; char xy_MessageBoxA[] = { 'M','e','s','s','a','g','e','B','o','x','A',0 }; FN_MessageBoxA fn_MessageBoxA = (FN_MessageBoxA)fn_GetProcAddress(fn_LoadLibraryA(xy_user32), xy_MessageBoxA); char xy_Hello[] = { 'H','e','l','l','o',' ','w','o','r','l','d',0 }; char xy_tip[] = { 't','i','p' }; fn_MessageBoxA(NULL, xy_Hello, xy_tip, MB_OK); return 0;}//内嵌汇编获取Kernel32的地址__declspec(naked) DWORD getKernel32(){ __asm { mov eax, fs:[30h] mov eax, [eax + 0ch] mov eax, [eax + 14h] mov eax, [eax] mov eax, [eax] mov eax, [eax + 10h] ret }}//获取GetProcAddress的地址FARPROC getProcAddress(HMODULE hModuleBase){ PIMAGE_DOS_HEADER lpDosHeader = (PIMAGE_DOS_HEADER)hModuleBase; PIMAGE_NT_HEADERS32 lpNtHeader = (PIMAGE_NT_HEADERS)((DWORD)hModuleBase + lpDosHeader->e_lfanew); if (!lpNtHeader->OptionalHeader.DataDirectory[IMAGE_DIRECTORY_ENTRY_EXPORT].Size) { return NULL; } if (!lpNtHeader->OptionalHeader.DataDirectory[IMAGE_DIRECTORY_ENTRY_EXPORT].VirtualAddress) { return NULL; } PIMAGE_EXPORT_DIRECTORY lpExports = (PIMAGE_EXPORT_DIRECTORY)((DWORD)hModuleBase + (DWORD)lpNtHeader->OptionalHeader.DataDirectory[IMAGE_DIRECTORY_ENTRY_EXPORT].VirtualAddress); PDWORD lpdwFunName = (PDWORD)((DWORD)hModuleBase + (DWORD)lpExports->AddressOfNames); PWORD lpword = (PWORD)((DWORD)hModuleBase + (DWORD)lpExports->AddressOfNameOrdinals); PDWORD lpdwFunAddr = (PDWORD)((DWORD)hModuleBase + (DWORD)lpExports->AddressOfFunctions); DWORD dwLoop = 0; FARPROC pRet = NULL; for (; dwLoop <= lpExports->NumberOfNames - 1; dwLoop++) { char* pFunName = (char*)(lpdwFunName[dwLoop] + (DWORD)hModuleBase); 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') { pRet = (FARPROC)(lpdwFunAddr[lpword[dwLoop]] + (DWORD)hModuleBase); break; } } return pRet;}
结果:运行exe文件创建了1.txt文件,并出现弹框。
规律:单文件函数的生成规律,与函数实现的先后顺序有关,而与函数的定义顺序无关。
例如:
#include<windows.h>#include<stdio.h>int FuncA(int a, int b){ puts("AAAA"); return a + b;}int FuncB(int a, int b){ puts("BBB"); return a + b;}int main(){ FuncA(1, 2); FuncB(2, 3); return 0;}
结果:在IDA中看到生成的exe文件中的函数顺序为FuncA,FuncB,main,与函数实现的先后顺序有关。通过函数的位置,可以得到两个函数之间的空间大小。
2.多文件函数生成的位置规律
规律:与包含文件的位置无关,与实际调用的顺序有关
//A.h#include<stdio.h>void A(){ puts("AAA");}//B.h#include<stdio.h>void B(){ puts("BBB");}//main#include"A.h"#include"B.h"int main(){
A(); B(); return 0;}
结果:
工程下的后缀名为vcxproj文件
修改顺序
可以看到生成的顺序发生了改变
Shellcode代码执行过程
ShellcodeStart-> ShellcodeEntry-> ShellcodeEnd
工程文件:
api.h文件:存放定义的的函数
header.h文件:存放定义的功能函数
0.entry.cpp文件:shellcode的入口点
a.start.cpp文件:shellcode执行(实现逻辑功能)
b.work.cpp文件:存放具体功能实现
z.end.cpp文件:shellcode结束
a.start.cpp文件和b.work.cpp文件分别管理逻辑功能和具体实现,更方便管理。
生成的文件顺序:
代码:
api.h
#pragma once#include<windows.h>//声明定义GetProcAddresstypedef FARPROC(WINAPI *FN_GetProcAddress)( _In_ HMODULE hModule, _In_ LPCSTR lpProcName );//定义LoadLibraryAtypedef HMODULE(WINAPI *FN_LoadLibraryA)( __in LPCSTR lpLibFileName );//定义MessageBoxAtypedef int (WINAPI *FN_MessageBoxA)( __in_opt HWND hWnd, __in_opt LPCSTR lpText, __in_opt LPCSTR lpCaption, __in UINT uType);//定义CreateFileAtypedef 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 );//定义一个指针typedef struct _FUNCTIONS{ FN_GetProcAddress fn_GetProcAddress; FN_LoadLibraryA fn_LoadLibraryA; FN_MessageBoxA fn_MessageBoxA; FN_CreateFileA fn_CreateFileA;}FUNCTIONS,*PFUNCTIONS;
header.h
#pragma once#include<windows.h>#include<stdio.h>#include"api.h"void ShellcodeStart();void ShellcodeEntry();void ShellcodeEnd();void CreateShellcode();void InitFunctions(PFUNCTIONS pFn);void CreateConfigFile(PFUNCTIONS pFn);
0.entry.cpp
#include "header.h"int EntryMain(){ CreateShellcode(); return 0;}void CreateShellcode() { HMODULE hMsvcrt = LoadLibraryA("msvcrt.dll"); //定义printf typedef int (__CRTDECL *FN_printf)( _In_z_ _Printf_format_string_ char const* const _Format, ...); FN_printf fn_printf = (FN_printf)GetProcAddress(hMsvcrt,"printf"); HANDLE hBin = CreateFileA("sh.bin", GENERIC_ALL, 0, NULL, CREATE_ALWAYS, 0, NULL); if (hBin == INVALID_HANDLE_VALUE) { //这里不能使用printf函数,因为修改了函数入口,找不到printf的地址,所有需要动态调用printf函数 //printf("create file error:%d\n", GetLastError()); fn_printf("create file error:%d\n", GetLastError()); return ; } DWORD dwSize = (DWORD)ShellcodeEnd - (DWORD)ShellcodeStart; DWORD dwWrite; WriteFile(hBin, ShellcodeStart, dwSize, &dwWrite, NULL); CloseHandle(hBin);}
a.start.cpp文件
#include "header.h"#include "api.h"__declspec(naked) void ShellcodeStart(){ __asm { jmp ShellcodeEntry }}//内嵌汇编获取Kernel32的地址__declspec(naked) DWORD getKernel32(){ __asm { mov eax, fs:[30h]; test eax, eax; js finished; mov eax, [eax + 0ch]; mov eax, [eax + 14h]; mov eax, [eax]; mov eax, [eax] mov eax, [eax + 10h] finished: ret }}//获取GetProcAddress的地址FARPROC getProcAddress(HMODULE hModuleBase){ PIMAGE_DOS_HEADER lpDosHeader = (PIMAGE_DOS_HEADER)hModuleBase; PIMAGE_NT_HEADERS32 lpNtHeader = (PIMAGE_NT_HEADERS)((DWORD)hModuleBase + lpDosHeader->e_lfanew); if (!lpNtHeader->OptionalHeader.DataDirectory[IMAGE_DIRECTORY_ENTRY_EXPORT].Size) { return NULL; } if (!lpNtHeader->OptionalHeader.DataDirectory[IMAGE_DIRECTORY_ENTRY_EXPORT].VirtualAddress) { return NULL; } PIMAGE_EXPORT_DIRECTORY lpExports = (PIMAGE_EXPORT_DIRECTORY)((DWORD)hModuleBase + (DWORD)lpNtHeader->OptionalHeader.DataDirectory[IMAGE_DIRECTORY_ENTRY_EXPORT].VirtualAddress); PDWORD lpdwFunName = (PDWORD)((DWORD)hModuleBase + (DWORD)lpExports->AddressOfNames); PWORD lpword = (PWORD)((DWORD)hModuleBase + (DWORD)lpExports->AddressOfNameOrdinals); PDWORD lpdwFunAddr = (PDWORD)((DWORD)hModuleBase + (DWORD)lpExports->AddressOfFunctions); DWORD dwLoop = 0; FARPROC pRet = NULL; for (; dwLoop <= lpExports->NumberOfNames - 1; dwLoop++) { char* pFunName = (char*)(lpdwFunName[dwLoop] + (DWORD)hModuleBase); 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') { pRet = (FARPROC)(lpdwFunAddr[lpword[dwLoop]] + (DWORD)hModuleBase); break; } } return pRet;}//动态调用地址void InitFunctions(PFUNCTIONS pFn) { //获取GetProcAddress真实地址 pFn->fn_GetProcAddress = (FN_GetProcAddress)getProcAddress((HMODULE)getKernel32()); //动态获取LoadLibraryA的地址 char xyLoadLibraryA[] = { 'L','o','a','d','L','i','b','r','a','r','y','A',0 }; pFn->fn_LoadLibraryA = (FN_LoadLibraryA)pFn->fn_GetProcAddress((HMODULE)getKernel32(), xyLoadLibraryA); //动态获取MessageBoxA的地址 char xy_user32[] = { 'u','s','e','r','3','2','.','d','l','l',0 }; char xy_MessageBoxA[] = { 'M','e','s','s','a','g','e','B','o','x','A',0 }; pFn->fn_MessageBoxA = (FN_MessageBoxA)pFn->fn_GetProcAddress(pFn->fn_LoadLibraryA(xy_user32), xy_MessageBoxA); //动态获取CreateFile的地址 char xyCreateFile[] = { 'C','r','e','a','t','F','i','l','e','A',0 }; pFn->fn_CreateFileA = (FN_CreateFileA)pFn->fn_GetProcAddress((HMODULE)getKernel32(), xyCreateFile);}//入口点void ShellcodeEntry(){ char xy_Hello[] = { 'H','e','l','l','o',' ','w','o','r','l','d',0 }; char xy_tip[] = { 't','i','p' }; FUNCTIONS fn; InitFunctions(&fn); CreateConfigFile(&fn);}
b.work.cpp
#include"api.h"#include<stdio.h>//存放功能void CreateConfigFile(PFUNCTIONS pFn){ char xyNewFile[] = { '1','.','t','x','t','\0' }; pFn->fn_CreateFileA(xyNewFile, GENERIC_WRITE, 0, NULL, CREATE_ALWAYS, 0, NULL);}
z.end.cpp
#include "header.h"void ShellcodeEnd(){}
用来运行提取出来的shellcode代码,保存在sh.bin文件,将sb.bin文件拖入加载器,即可执行。
#include<stdio.h>#include<windows.h>int main(int argc,char* argv[]){ //打开文件 HANDLE hFile = CreateFileA(argv[1], GENERIC_READ, 0, NULL, OPEN_ALWAYS, 0, NULL); if (hFile == INVALID_HANDLE_VALUE) { printf("Oen file error:%d\n", GetLastError); return -1; } DWORD dwSize; dwSize = GetFileSize(hFile, NULL); LPVOID lpAddress = VirtualAlloc(NULL, dwSize, MEM_COMMIT, PAGE_EXECUTE_READWRITE); //内存分配是否成功 if (lpAddress ==NULL) { printf("VirtualAlloc error:%d\n", GetLastError); CloseHandle(hFile); return -1; } DWORD dwRead; ReadFile(hFile,lpAddress,dwSize,&dwRead, 0); //内嵌汇编 __asm { call lpAddress } _flushall(); system("pause"); return 0;}
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