Windows Shellcode学习笔记——shellcode的提取与测试
0x00 前言
之前在《Windows Shellcode学习笔记——通过VisualStudio生成shellcode》介绍了使用C++编写（不使用内联汇编），实现动态获取API地址并调用，对其反汇编提取shellcode的方法，并开源了测试代码。
接下来在对shellcode进行提取的过程中，发现了当时开源代码的一些bug，所以本文着重解决测试代码的bug，并介绍使用C++开发shellcode需要考虑的一些问题。
存在bug的测试代码下载地址：
https://github.com/3gstudent/Shellcode-Generater/blob/master/shellcode.cpp
0x01 简介
简单的shellcode提取流程：
- 使用c++开发代码
- 更改VisualStudio编译配置
- 生成exe
- 在IDA下打开生成的exe，获得机器码
由于是动态获取API地址并调用，所以为了保证shellcode的兼容性，代码中不能出现固定地址，并且要尽量避免使用全局变量，如果代码中包含子函数，根据调用方式，还有注意各个函数之间的排列顺序（起始函数放于最前）
0x02 Bug修复
配置三个编译选项:release、禁用优化、禁用/GS
将代码编译，然后使用IDA提取机器码作为shellcode
在实际调试过程中，发现代码存在bug：
1、代码中应合理处理全局变量
在代码中使用全局变量
FARPROC(WINAPI* GetProcAddressAPI)(HMODULE, LPCSTR);
HMODULE(WINAPI* LoadLibraryWAPI)(LPCWSTR);
在编译后会成为一个固定地址，导致shellcode无法兼容不同环境
最简单直接的方式是在shellcode中尽量避免全局变量
2、函数声明方式需要修改
修改全局变量后，以下代码需要修改：
MESSAGEBOXA_INITIALIZE MeassageboxA_MyOwn = reinterpret_cast<MESSAGEBOXA_INITIALIZE>(GetProcAddressAPI(LoadLibraryWAPI(struser32), MeassageboxA_api));
MeassageboxA_MyOwn(NULL, NULL, NULL, 0);
需要全部换成typedef的函数声明方式
3、函数调用顺序
如果使用以下方式加载shellcode：
(*(int(*)()) sc)();
起始函数的定义应该位于这段shellcode的最前面（和函数声明的顺序无关）
注：
shellcode如果包含子函数，应该保证各个函数放在一段连续的地址中，并且起始函数置于最前面，这样在提取机器码后，可以直接加载起始函数执行shellcode
综上，给出新的完整代码：
#include <windows.h>
#include <Winternl.h>
#pragma optimize( "", off )
void shell_code();
HANDLE GetKernel32Handle();
BOOL __ISUPPER__(__in CHAR c);
CHAR __TOLOWER__(__in CHAR c);
UINT __STRLEN__(__in LPSTR lpStr1);
UINT __STRLENW__(__in LPWSTR lpStr1);
LPWSTR __STRSTRIW__(__in LPWSTR lpStr1, __in LPWSTR lpStr2);
INT __STRCMPI__(__in LPSTR lpStr1, __in LPSTR lpStr2);
INT __STRNCMPIW__(__in LPWSTR lpStr1, __in LPWSTR lpStr2, __in DWORD dwLen);
LPVOID __MEMCPY__(__in LPVOID lpDst, __in LPVOID lpSrc, __in DWORD dwCount);
typedef FARPROC(WINAPI* GetProcAddressAPI)(HMODULE, LPCSTR);
typedef HMODULE(WINAPI* LoadLibraryWAPI)(LPCWSTR);
typedef ULONG (WINAPI *MESSAGEBOXAPI)(HWND, LPWSTR, LPWSTR, ULONG);
void shell_code() {
LoadLibraryWAPI loadlibrarywapi = 0;
GetProcAddressAPI getprocaddressapi=0;
MESSAGEBOXAPI messageboxapi=0;
wchar_t struser32[] = { L'u', L's', L'e', L'r', L'3',L'2', L'.', L'd', L'l', L'l', 0 };
char MeassageboxA_api[] = { 'M', 'e', 's', 's', 'a', 'g', 'e', 'B', 'o', 'x', 'A', 0 };
HANDLE hKernel32 = GetKernel32Handle();
if (hKernel32 == INVALID_HANDLE_VALUE) {
return;
}
LPBYTE lpBaseAddr = (LPBYTE)hKernel32;
PIMAGE_DOS_HEADER lpDosHdr = (PIMAGE_DOS_HEADER)lpBaseAddr;
PIMAGE_NT_HEADERS pNtHdrs = (PIMAGE_NT_HEADERS)(lpBaseAddr + lpDosHdr->e_lfanew);
PIMAGE_EXPORT_DIRECTORY pExportDir = (PIMAGE_EXPORT_DIRECTORY)(lpBaseAddr + pNtHdrs->OptionalHeader.DataDirectory[IMAGE_DIRECTORY_ENTRY_EXPORT].VirtualAddress);
LPDWORD pNameArray = (LPDWORD)(lpBaseAddr + pExportDir->AddressOfNames);
LPDWORD pAddrArray = (LPDWORD)(lpBaseAddr + pExportDir->AddressOfFunctions);
LPWORD pOrdArray = (LPWORD)(lpBaseAddr + pExportDir->AddressOfNameOrdinals);
CHAR strLoadLibraryA[] = { 'L', 'o', 'a', 'd', 'L', 'i', 'b', 'r', 'a', 'r', 'y', 'W', 0x0 };
CHAR strGetProcAddress[] = { 'G', 'e', 't', 'P', 'r', 'o', 'c', 'A', 'd', 'd', 'r', 'e', 's', 's', 0x0 };
for (UINT i = 0; i < pExportDir->NumberOfNames; i++) {
LPSTR pFuncName = (LPSTR)(lpBaseAddr + pNameArray[i]);
if (!__STRCMPI__(pFuncName, strGetProcAddress)) {
getprocaddressapi=(GetProcAddressAPI)(lpBaseAddr + pAddrArray[pOrdArray[i]]);
}
else if (!__STRCMPI__(pFuncName, strLoadLibraryA)) {
loadlibrarywapi=(LoadLibraryWAPI) (lpBaseAddr + pAddrArray[pOrdArray[i]]);
}
if (getprocaddressapi != nullptr && loadlibrarywapi != nullptr) {
messageboxapi=(MESSAGEBOXAPI)getprocaddressapi(loadlibrarywapi(struser32), MeassageboxA_api);
messageboxapi(NULL, NULL, NULL, 0);
return;
}
}
}
inline BOOL __ISUPPER__(__in CHAR c) {
return ('A' <= c) && (c <= 'Z');
};
inline CHAR __TOLOWER__(__in CHAR c) {
return __ISUPPER__(c) ? c - 'A' + 'a' : c;
};
UINT __STRLEN__(__in LPSTR lpStr1)
{
UINT i = 0;
while (lpStr1[i] != 0x0)
i++;
return i;
}
UINT __STRLENW__(__in LPWSTR lpStr1)
{
UINT i = 0;
while (lpStr1[i] != L'\0')
i++;
return i;
}
LPWSTR __STRSTRIW__(__in LPWSTR lpStr1, __in LPWSTR lpStr2)
{
CHAR c = __TOLOWER__(((PCHAR)(lpStr2++))[0]);
if (!c)
return lpStr1;
UINT dwLen = __STRLENW__(lpStr2);
do
{
CHAR sc;
do
{
sc = __TOLOWER__(((PCHAR)(lpStr1)++)[0]);
if (!sc)
return NULL;
} while (sc != c);
} while (__STRNCMPIW__(lpStr1, lpStr2, dwLen) != 0);
return (lpStr1 - 1); // FIXME -2 ?
}
INT __STRCMPI__(
__in LPSTR lpStr1,
__in LPSTR lpStr2)
{
int v;
CHAR c1, c2;
do
{
c1 = *lpStr1++;
c2 = *lpStr2++;
// The casts are necessary when pStr1 is shorter & char is signed
v = (UINT)__TOLOWER__(c1) - (UINT)__TOLOWER__(c2);
} while ((v == 0) && (c1 != '\0') && (c2 != '\0'));
return v;
}
INT __STRNCMPIW__(
__in LPWSTR lpStr1,
__in LPWSTR lpStr2,
__in DWORD dwLen)
{
int v;
CHAR c1, c2;
do {
dwLen--;
c1 = ((PCHAR)lpStr1++)[0];
c2 = ((PCHAR)lpStr2++)[0];
/* The casts are necessary when pStr1 is shorter & char is signed */
v = (UINT)__TOLOWER__(c1) - (UINT)__TOLOWER__(c2);
} while ((v == 0) && (c1 != 0x0) && (c2 != 0x0) && dwLen > 0);
return v;
}
LPSTR __STRCAT__(
__in LPSTR strDest,
__in LPSTR strSource)
{
LPSTR d = strDest;
LPSTR s = strSource;
while (*d) d++;
do { *d++ = *s++; } while (*s);
*d = 0x0;
return strDest;
}
LPVOID __MEMCPY__(
__in LPVOID lpDst,
__in LPVOID lpSrc,
__in DWORD dwCount)
{
LPBYTE s = (LPBYTE)lpSrc;
LPBYTE d = (LPBYTE)lpDst;
while (dwCount--)
*d++ = *s++;
return lpDst;
}
HANDLE GetKernel32Handle() {
HANDLE hKernel32 = INVALID_HANDLE_VALUE;
#ifdef _WIN64
PPEB lpPeb = (PPEB)__readgsqword(0x60);
#else
PPEB lpPeb = (PPEB)__readfsdword(0x30);
#endif
PLIST_ENTRY pListHead = &lpPeb->Ldr->InMemoryOrderModuleList;
PLIST_ENTRY pListEntry = pListHead->Flink;
WCHAR strDllName[MAX_PATH];
WCHAR strKernel32[] = { 'k', 'e', 'r', 'n', 'e', 'l', '3', '2', '.', 'd', 'l', 'l', L'\0' };
while (pListEntry != pListHead) {
PLDR_DATA_TABLE_ENTRY pModEntry = CONTAINING_RECORD(pListEntry, LDR_DATA_TABLE_ENTRY, InMemoryOrderLinks);
if (pModEntry->FullDllName.Length) {
DWORD dwLen = pModEntry->FullDllName.Length;
__MEMCPY__(strDllName, pModEntry->FullDllName.Buffer, dwLen);
strDllName[dwLen / sizeof(WCHAR)] = L'\0';
if (__STRSTRIW__(strDllName, strKernel32)) {
hKernel32 = pModEntry->DllBase;
break;
}
}
pListEntry = pListEntry->Flink;
}
return hKernel32;
}
int main()
{
printf("1");
shell_code();
printf("2");
return 0;
}
0x03 Shellcode提取
将以上代码编译成exe后使用IDA打开，查看Function Window，找到各子函数起始地址
如图
可以看到各个函数保存在一段连续的地址，并且shellcode起始函数位于最开始
双击第一个函数shell_code(void)，进入IDA文本视图，可查看shell_code(void)函数具体在exe文件中的位置为00000400
如图
查看main函数在exe文件中的位置为00000A00
如图
结合c代码的结构，推断出在exe文件中的偏移范围00000400-00000A00即为我们需要的机器码
使用十六进制编辑器将其中的机器码提取并保存到文件中，文件中的内容即我们需要的shellcode
当然，以上手动提取机器码并保存到文件的功能可通过程序自动实现，完整代码如下：
#include <stdafx.h>
#include <windows.h>
#include <Winternl.h>
#pragma optimize( "", off )
void shell_code();
HANDLE GetKernel32Handle();
BOOL __ISUPPER__(__in CHAR c);
CHAR __TOLOWER__(__in CHAR c);
UINT __STRLEN__(__in LPSTR lpStr1);
UINT __STRLENW__(__in LPWSTR lpStr1);
LPWSTR __STRSTRIW__(__in LPWSTR lpStr1, __in LPWSTR lpStr2);
INT __STRCMPI__(__in LPSTR lpStr1, __in LPSTR lpStr2);
INT __STRNCMPIW__(__in LPWSTR lpStr1, __in LPWSTR lpStr2, __in DWORD dwLen);
LPVOID __MEMCPY__(__in LPVOID lpDst, __in LPVOID lpSrc, __in DWORD dwCount);
typedef FARPROC(WINAPI* GetProcAddressAPI)(HMODULE, LPCSTR);
typedef HMODULE(WINAPI* LoadLibraryWAPI)(LPCWSTR);
typedef ULONG (WINAPI *MESSAGEBOXAPI)(HWND, LPWSTR, LPWSTR, ULONG);
void shell_code() {
LoadLibraryWAPI loadlibrarywapi = 0;
GetProcAddressAPI getprocaddressapi=0;
MESSAGEBOXAPI messageboxapi=0;
wchar_t struser32[] = { L'u', L's', L'e', L'r', L'3',L'2', L'.', L'd', L'l', L'l', 0 };
char MeassageboxA_api[] = { 'M', 'e', 's', 's', 'a', 'g', 'e', 'B', 'o', 'x', 'A', 0 };
HANDLE hKernel32 = GetKernel32Handle();
if (hKernel32 == INVALID_HANDLE_VALUE) {
return;
}
LPBYTE lpBaseAddr = (LPBYTE)hKernel32;
PIMAGE_DOS_HEADER lpDosHdr = (PIMAGE_DOS_HEADER)lpBaseAddr;
PIMAGE_NT_HEADERS pNtHdrs = (PIMAGE_NT_HEADERS)(lpBaseAddr + lpDosHdr->e_lfanew);
PIMAGE_EXPORT_DIRECTORY pExportDir = (PIMAGE_EXPORT_DIRECTORY)(lpBaseAddr + pNtHdrs->OptionalHeader.DataDirectory[IMAGE_DIRECTORY_ENTRY_EXPORT].VirtualAddress);
LPDWORD pNameArray = (LPDWORD)(lpBaseAddr + pExportDir->AddressOfNames);
LPDWORD pAddrArray = (LPDWORD)(lpBaseAddr + pExportDir->AddressOfFunctions);
LPWORD pOrdArray = (LPWORD)(lpBaseAddr + pExportDir->AddressOfNameOrdinals);
CHAR strLoadLibraryA[] = { 'L', 'o', 'a', 'd', 'L', 'i', 'b', 'r', 'a', 'r', 'y', 'W', 0x0 };
CHAR strGetProcAddress[] = { 'G', 'e', 't', 'P', 'r', 'o', 'c', 'A', 'd', 'd', 'r', 'e', 's', 's', 0x0 };
for (UINT i = 0; i < pExportDir->NumberOfNames; i++) {
LPSTR pFuncName = (LPSTR)(lpBaseAddr + pNameArray[i]);
if (!__STRCMPI__(pFuncName, strGetProcAddress)) {
getprocaddressapi=(GetProcAddressAPI)(lpBaseAddr + pAddrArray[pOrdArray[i]]);
}
else if (!__STRCMPI__(pFuncName, strLoadLibraryA)) {
loadlibrarywapi=(LoadLibraryWAPI) (lpBaseAddr + pAddrArray[pOrdArray[i]]);
}
if (getprocaddressapi != nullptr && loadlibrarywapi != nullptr) {
messageboxapi=(MESSAGEBOXAPI)getprocaddressapi(loadlibrarywapi(struser32), MeassageboxA_api);
messageboxapi(NULL, NULL, NULL, 0);
return;
}
}
}
inline BOOL __ISUPPER__(__in CHAR c) {
return ('A' <= c) && (c <= 'Z');
};
inline CHAR __TOLOWER__(__in CHAR c) {
return __ISUPPER__(c) ? c - 'A' + 'a' : c;
};
UINT __STRLEN__(__in LPSTR lpStr1)
{
UINT i = 0;
while (lpStr1[i] != 0x0)
i++;
return i;
}
UINT __STRLENW__(__in LPWSTR lpStr1)
{
UINT i = 0;
while (lpStr1[i] != L'\0')
i++;
return i;
}
LPWSTR __STRSTRIW__(__in LPWSTR lpStr1, __in LPWSTR lpStr2)
{
CHAR c = __TOLOWER__(((PCHAR)(lpStr2++))[0]);
if (!c)
return lpStr1;
UINT dwLen = __STRLENW__(lpStr2);
do
{
CHAR sc;
do
{
sc = __TOLOWER__(((PCHAR)(lpStr1)++)[0]);
if (!sc)
return NULL;
} while (sc != c);
} while (__STRNCMPIW__(lpStr1, lpStr2, dwLen) != 0);
return (lpStr1 - 1); // FIXME -2 ?
}
INT __STRCMPI__(
__in LPSTR lpStr1,
__in LPSTR lpStr2)
{
int v;
CHAR c1, c2;
do
{
c1 = *lpStr1++;
c2 = *lpStr2++;
// The casts are necessary when pStr1 is shorter & char is signed
v = (UINT)__TOLOWER__(c1) - (UINT)__TOLOWER__(c2);
} while ((v == 0) && (c1 != '\0') && (c2 != '\0'));
return v;
}
INT __STRNCMPIW__(
__in LPWSTR lpStr1,
__in LPWSTR lpStr2,
__in DWORD dwLen)
{
int v;
CHAR c1, c2;
do {
dwLen--;
c1 = ((PCHAR)lpStr1++)[0];
c2 = ((PCHAR)lpStr2++)[0];
/* The casts are necessary when pStr1 is shorter & char is signed */
v = (UINT)__TOLOWER__(c1) - (UINT)__TOLOWER__(c2);
} while ((v == 0) && (c1 != 0x0) && (c2 != 0x0) && dwLen > 0);
return v;
}
LPSTR __STRCAT__(
__in LPSTR strDest,
__in LPSTR strSource)
{
LPSTR d = strDest;
LPSTR s = strSource;
while (*d) d++;
do { *d++ = *s++; } while (*s);
*d = 0x0;
return strDest;
}
LPVOID __MEMCPY__(
__in LPVOID lpDst,
__in LPVOID lpSrc,
__in DWORD dwCount)
{
LPBYTE s = (LPBYTE)lpSrc;
LPBYTE d = (LPBYTE)lpDst;
while (dwCount--)
*d++ = *s++;
return lpDst;
}
HANDLE GetKernel32Handle() {
HANDLE hKernel32 = INVALID_HANDLE_VALUE;
#ifdef _WIN64
PPEB lpPeb = (PPEB)__readgsqword(0x60);
#else
PPEB lpPeb = (PPEB)__readfsdword(0x30);
#endif
PLIST_ENTRY pListHead = &lpPeb->Ldr->InMemoryOrderModuleList;
PLIST_ENTRY pListEntry = pListHead->Flink;
WCHAR strDllName[MAX_PATH];
WCHAR strKernel32[] = { 'k', 'e', 'r', 'n', 'e', 'l', '3', '2', '.', 'd', 'l', 'l', L'\0' };
while (pListEntry != pListHead) {
PLDR_DATA_TABLE_ENTRY pModEntry = CONTAINING_RECORD(pListEntry, LDR_DATA_TABLE_ENTRY, InMemoryOrderLinks);
if (pModEntry->FullDllName.Length) {
DWORD dwLen = pModEntry->FullDllName.Length;
__MEMCPY__(strDllName, pModEntry->FullDllName.Buffer, dwLen);
strDllName[dwLen / sizeof(WCHAR)] = L'\0';
if (__STRSTRIW__(strDllName, strKernel32)) {
hKernel32 = pModEntry->DllBase;
break;
}
}
pListEntry = pListEntry->Flink;
}
return hKernel32;
}
void __declspec(naked) END_SHELLCODE(void) {}
int main()
{
shell_code();
FILE *output_file;
fopen_s(&output_file,"shellcode.bin", "wb");
fwrite(shell_code, (int)END_SHELLCODE - (int)shell_code, 1, output_file);
fclose(output_file);
return 0;
}
注：
打开文件需要以”wb”模式打开二进制文件 如果以”w”模式，写入文件的过程中，0A字符会被替换为0D0A,导致shellcode出现问题
0x04 Shellcode测试
使用以下代码可读取文件中保存的shellcode，加载并测试其功能：
#include <windows.h>
size_t GetSize(char * szFilePath)
{
size_t size;
FILE* f = fopen(szFilePath, "rb");
fseek(f, 0, SEEK_END);
size = ftell(f);
rewind(f);
fclose(f);
return size;
}
unsigned char* ReadBinaryFile(char *szFilePath, size_t *size)
{
unsigned char *p = NULL;
FILE* f = NULL;
size_t res = 0;
*size = GetSize(szFilePath);
if (*size == 0) return NULL;
f = fopen(szFilePath, "rb");
if (f == NULL)
{
printf("Binary file does not exists!\n");
return 0;
}
p = new unsigned char[*size];
rewind(f);
res = fread(p, sizeof(unsigned char), *size, f);
fclose(f);
if (res == 0)
{
delete[] p;
return NULL;
}
return p;
}
int main(int argc, char* argv[])
{
char *szFilePath="c:\\test\\shellcode.bin";
unsigned char *BinData = NULL;
size_t size = 0;
BinData = ReadBinaryFile(szFilePath, &size);
void *sc = VirtualAlloc(0, size, MEM_RESERVE | MEM_COMMIT, PAGE_EXECUTE_READWRITE);
if (sc == NULL)
return 0;
memcpy(sc, BinData, size);
(*(int(*)()) sc)();
return 0;
}