实现一个压缩壳,并给它加点“料”

语言: CN / TW / HK

本文为看雪论坛优秀文章

看雪论坛作者ID:橘喵Cat

前言

实现压缩壳,必须对PE格式十分熟悉,其次,解压缩代码需要编写shellcode,也是十分麻烦的环节。有了两者的结合,我们才能写好一个真正的压缩壳。

设计思路

首先上一张图,让大家直观地感受到一个壳程序是如何运行起来的。

左边是壳PE,壳程序有一个PE头,节表1是空节,用来存放解压缩后的原程序PE,节表2此时存储的是压缩后的原PE。节表3则是壳代码节,壳PE运行起来后,首先就是进入入口点,运行节表3的代码,解压缩节表2,然后将结果覆盖PE头+节表1的位置,修复完导入表、重定位表,jmp到原程序的入口点处即可。

原理不变,我这里加了点“料”,新增了节4和节5,存储了相关的信息,让压缩壳的脱壳过程变难,往后看就知道了。

壳代码实现

1.为了生成一个新的壳PE,我们一步步来,首先是PE头,俗话说靠山吃山,靠水吃水,这个PE头我就直接拿原程序的PE头来代替了,只不过需要改一些数据:

NumberOfSections --节表数量,要改为5
AddressOfEntryPoint --入口点,要改为节表3里的代码入口
SizeOfImage --PE在内存中的大小,要改为新的PE的内存大小
pSecHdr --节表头,要拓展为5个节表

void CPacker::GetNewPeHdr()
{
//拷贝原PE的PE头
m_dwNewPeHdrSize = m_pNtHdr->OptionalHeader.SizeOfHeaders;
m_pNewPeHdr = new BYTE[m_dwNewPeHdrSize];
CopyMemory(m_pNewPeHdr, m_pDosHdr, m_dwNewPeHdrSize);

//修改
auto pDosHdr = (PIMAGE_DOS_HEADER)m_pNewPeHdr;
auto pNtHdr = (PIMAGE_NT_HEADERS)(m_pNewPeHdr + pDosHdr->e_lfanew);
auto pSecHdr = (PIMAGE_SECTION_HEADER)
((LPBYTE)&pNtHdr->OptionalHeader + pNtHdr->FileHeader.SizeOfOptionalHeader);

pNtHdr->FileHeader.NumberOfSections = 5;
pNtHdr->OptionalHeader.AddressOfEntryPoint = m_newSecHdr[2].VirtualAddress;
pNtHdr->OptionalHeader.SizeOfImage = m_newSecHdr[4].VirtualAddress + m_newSecHdr[4].Misc.VirtualSize;
//清空DataDirectory目录
ZeroMemory(pNtHdr->OptionalHeader.DataDirectory, sizeof(pNtHdr->OptionalHeader.DataDirectory));

//修改新的节表头
CopyMemory(pSecHdr, m_newSecHdr, sizeof(m_newSecHdr));

}

2.新PE头里一些需要修改的数据,比如SizeOfImage,我们目前还没有,需要等我们构造出节表1、2、3、4、5之后,才知道。接下来,先构造节表1的表头,节表1是个空节,它的大小只要够存放原程序的节表即可,多给一点也没关系,我这里直接给了SizeOfImage。(由于是空节,所以这里并不需要考虑节表1的数据内容)

//空节
strcpy((char*)m_newSecHdr[0].Name, ".cr42");
m_newSecHdr[0].Misc.VirtualSize = m_pNtHdr->OptionalHeader.SizeOfImage;
m_newSecHdr[0].VirtualAddress = m_pSecHdr[0].VirtualAddress;
m_newSecHdr[0].SizeOfRawData = 0;
m_newSecHdr[0].PointerToRawData = 0;
m_newSecHdr[0].Characteristics =
IMAGE_SCN_MEM_EXECUTE | IMAGE_SCN_MEM_WRITE | IMAGE_SCN_MEM_READ;

3.接着是节表2,这个节要存放原PE的压缩数据,先设计表头(使用了PointerToRelocations和PointerToLinenumbers这两个没啥用的字段,存放压缩大小信息,留着给后面shellcode用)。

//压缩数据节
strcpy((char*)m_newSecHdr[1].Name, ".data");
m_newSecHdr[1].Misc.VirtualSize = GetAlign(m_dwComSecSize, m_pNtHdr->OptionalHeader.SectionAlignment);
m_newSecHdr[1].VirtualAddress = m_newSecHdr[0].VirtualAddress + m_newSecHdr[0].Misc.VirtualSize;
m_newSecHdr[1].SizeOfRawData = m_dwComSecSize;
m_newSecHdr[1].PointerToRawData = m_pNtHdr->OptionalHeader.SizeOfHeaders;
m_newSecHdr[1].Characteristics = IMAGE_SCN_MEM_READ;

m_newSecHdr[1].PointerToRelocations = m_dwComSize; //压缩后大小
m_newSecHdr[1].PointerToLinenumbers = m_dwSrcPeSize;//压缩前大小

然后将PE压缩,压缩前我把节表、导入表、重定位表保存并清空,到时候由shellcode进行还原。

bool CPacker::GetCompressData()
{
COMPRESSOR_HANDLE hCompressor = NULL;
BOOL Success = CreateCompressor(
COMPRESS_ALGORITHM_XPRESS_HUFF,
NULL,
&hCompressor
);

m_pComData = new BYTE[m_dwSrcPeSize + 0x28];
LPBYTE m_pSrcPeTmp = new BYTE[m_dwSrcPeSize];
CopyMemory(m_pSrcPeTmp, m_pSrcPe, m_dwSrcPeSize);

PIMAGE_DOS_HEADER m_pDosHdrTmp = (PIMAGE_DOS_HEADER)m_pSrcPeTmp;
PIMAGE_NT_HEADERS m_pNtHdrTmp = (PIMAGE_NT_HEADERS)(m_pSrcPeTmp + m_pDosHdrTmp->e_lfanew);
PIMAGE_SECTION_HEADER m_pSecHdrTmp = (PIMAGE_SECTION_HEADER)
((LPBYTE)&m_pNtHdrTmp->OptionalHeader + m_pNtHdrTmp->FileHeader.SizeOfOptionalHeader);

//1.在压缩前,把节表保存并清空
nSecNum = m_pNtHdrTmp->FileHeader.NumberOfSections;
CopyMemory(m_pSaveSecHdr, m_pSecHdrTmp, nSecNum * 40);
ZeroMemory(m_pSecHdrTmp, nSecNum * 40);

//2.把导入表保存并清空
m_pImportAddr = m_pNtHdrTmp->OptionalHeader.DataDirectory[1].VirtualAddress;
nImpSize = m_pNtHdrTmp->OptionalHeader.DataDirectory[1].Size;
ZeroMemory(&(m_pNtHdrTmp->OptionalHeader.DataDirectory[1]), 8);

//3.把重定位表保存并清空
m_pRelocAddr = m_pNtHdrTmp->OptionalHeader.DataDirectory[5].VirtualAddress;
nRelocSize = m_pNtHdrTmp->OptionalHeader.DataDirectory[5].Size;
ZeroMemory(&(m_pNtHdrTmp->OptionalHeader.DataDirectory[5]), 8);



Success = Compress(
hCompressor,
m_pSrcPeTmp,
m_dwSrcPeSize,
m_pComData,
m_dwSrcPeSize + 0x28,
&m_dwComSize
);


return true;
}

4.接着是节表3,该节表存放的是解压缩PE、还原导入表、重定位表,运行原程序的至关重要的shellcode,先设计表头。

//代码节
strcpy((char*)m_newSecHdr[2].Name, ".text");
m_newSecHdr[2].Misc.VirtualSize = GetAlign(m_dwCodeSecSize, m_pNtHdr->OptionalHeader.SectionAlignment);
m_newSecHdr[2].VirtualAddress = m_newSecHdr[1].VirtualAddress + m_newSecHdr[1].Misc.VirtualSize;
m_newSecHdr[2].SizeOfRawData = m_dwCodeSecSize;
m_newSecHdr[2].PointerToRawData = m_newSecHdr[1].PointerToRawData + m_newSecHdr[1].SizeOfRawData;
m_newSecHdr[2].Characteristics = IMAGE_SCN_MEM_EXECUTE | IMAGE_SCN_MEM_WRITE | IMAGE_SCN_MEM_READ;

至于节表3的数据内容,也就是shellcode,等我把节表、PE设计完,我再说。


5.接着是节表4,节表4是我额外增加的一个,用来存储步骤3中保存的原节表表头、原导入表、原重定位表,首先设计节表4表头。

//存放原节表、导入表、重定位表的节
strcpy((char*)m_newSecHdr[3].Name, ".info");
m_newSecHdr[3].Misc.VirtualSize = GetAlign(m_dwTableSecSize, m_pNtHdr->OptionalHeader.SectionAlignment);
m_newSecHdr[3].VirtualAddress = m_newSecHdr[2].VirtualAddress + m_newSecHdr[2].Misc.VirtualSize;
m_newSecHdr[3].SizeOfRawData = m_dwTableSecSize;
m_newSecHdr[3].PointerToRawData = m_newSecHdr[2].PointerToRawData + m_newSecHdr[2].SizeOfRawData;
m_newSecHdr[3].Characteristics = IMAGE_SCN_MEM_EXECUTE | IMAGE_SCN_MEM_WRITE | IMAGE_SCN_MEM_READ;

然后把刚才保存的原节表表头、原导入表、原重定位表信息,按顺序写入到缓冲区里。

bool CPacker::GetTable()
{
m_dwTableSize = nSecNum * 40 + 4 + 8 + 8;
m_pTable = new BYTE[m_dwTableSize];
RtlCopyMemory(m_pTable, &nSecNum, 4);
RtlCopyMemory(m_pTable + 4, m_pSaveSecHdr, nSecNum * 40);
RtlCopyMemory(m_pTable + 4 + nSecNum * 40, &m_pImportAddr, 4);
RtlCopyMemory(m_pTable + 4 + nSecNum * 40 + 4, &nImpSize, 4);
RtlCopyMemory(m_pTable + 4 + nSecNum * 40 + 4 + 4, &m_pRelocAddr, 4);
RtlCopyMemory(m_pTable + 4 + nSecNum * 40 + 4 + 4 + 4, &nRelocSize, 4);

return true;
}

6.还剩最后一个节表5,是一个空节,壳代码还原原PE时,要还原导入表,于是这个节的作用就体现出来了,shellcode在这里玩了一波偷梁换柱,直接毙掉了x64dbg的脱壳后导入表自动修复功能,等会介绍shellcode的时候你们就知道了。设计节表5的表头:

//绕过x64搜索导入表的节(空节)
strcpy((char*)m_newSecHdr[4].Name, ".imp");
m_newSecHdr[4].Misc.VirtualSize = GetAlign(0x10000, m_pNtHdr->OptionalHeader.SectionAlignment);
m_newSecHdr[4].VirtualAddress = m_newSecHdr[3].VirtualAddress + m_newSecHdr[3].Misc.VirtualSize;
m_newSecHdr[4].SizeOfRawData = 0;
m_newSecHdr[4].PointerToRawData = m_newSecHdr[3].PointerToRawData + m_newSecHdr[2].SizeOfRawData;
m_newSecHdr[4].Characteristics = IMAGE_SCN_MEM_EXECUTE | IMAGE_SCN_MEM_WRITE | IMAGE_SCN_MEM_READ;

至此,新的壳PE结构我们就设计好了,然后将新PE头、节表234写入到新文件(节表1、5是空节,不用写入),就大功告成,加壳完毕!

bool CPacker::WriteNewPe(CString strNewPe)
{
//创建文件
HANDLE hFile = CreateFile(strNewPe,
GENERIC_WRITE,
0,
NULL,
CREATE_ALWAYS,
FILE_ATTRIBUTE_NORMAL,
NULL);

//写入PE头
DWORD dwBytesWrited = 0;
WriteFile(hFile, m_pNewPeHdr, m_dwNewPeHdrSize, &dwBytesWrited, NULL);

//写入数据节
WriteFile(hFile, m_pComSec, m_dwComSecSize, &dwBytesWrited, NULL);

//写入代码节
WriteFile(hFile, m_pCodeSec, m_dwCodeSecSize, &dwBytesWrited, NULL);

//写入存放表数据节
WriteFile(hFile, m_pTableSec, m_dwTableSecSize, &dwBytesWrited, NULL);

CloseHandle(hFile);

return true;
}

shellcode代码实现

由于壳PE可能是随机基址,所以执行shellcode时,一定要确保它的代码跟地址无关。我的shellcode是在VS上编译的,为了保证VS不会生成多余的代码,要修改以下几个设置:

1.使用Release版(Debug会加地址有关代码)
2.不使用main函数,自己定义一个,放在链接器->高级->入口点(main不是程序真正入口点)
3.关掉代码生成->安全检查
4.关掉增强指令集
5.关掉全程序优化

然后就是最麻烦的shellcode代码编写了。首先要清楚shellcode代码的功能:

1.解压缩节表2里面的压缩数据
2.将解压缩数据覆盖到PE头处,连带着空节表1也被覆盖
3.还原节表、导入表、重定位表

1.要解压缩,那么必定要调用库的API,如果直接调用的话,call的就是死地址,违背了地址无关原则。那么使用LoadLibrary然后GetProcAddress?显然也不行,LoadLibrary和GetProcAddress也是死地址,所以我们要自己实现LoadLibrary和GetProcAddress的功能。


首先通过_PEB来拿到kernel32的模块基址。

HMODULE GetKernel32()
{
HMODULE hKer;
__asm {

mov eax, dword ptr fs:[0x30]
mov eax, dword ptr[eax + 0x0C]
mov eax, dword ptr[eax + 0x0C]
mov eax, dword ptr[eax]
mov eax, dword ptr[eax]
mov eax, dword ptr[eax + 0x18]
mov hKer, eax
}

return hKer;
}

然后通过kernel32的导出函数表,拿到GetProcAddress函数地址,代码如下:

FARPROC MyGetProcAddress(HMODULE hMod, LPCSTR lpProcName) {

IMAGE_DOS_HEADER* pDosHdr;
IMAGE_NT_HEADERS* pNTHdr;
IMAGE_EXPORT_DIRECTORY* pExpDir;
DWORD pAddrTbl;
DWORD pNameTbl;
DWORD pOrdTbl;

//解析dos头
pDosHdr = (IMAGE_DOS_HEADER*)hMod;

//nt头
pNTHdr = (IMAGE_NT_HEADERS*)(pDosHdr->e_lfanew + (DWORD)hMod);

//获取导出表
pExpDir = (IMAGE_EXPORT_DIRECTORY*)(pNTHdr->OptionalHeader.DataDirectory[0].VirtualAddress + (DWORD)hMod);

//导出函数地址表
pAddrTbl = (DWORD)(pExpDir->AddressOfFunctions + (DWORD)hMod);

//导出函数名称表
pNameTbl = (DWORD)(pExpDir->AddressOfNames + (DWORD)hMod);

//导出序号表
pOrdTbl = (DWORD)(pExpDir->AddressOfNameOrdinals + (DWORD)hMod);

//判断是序号还是名称
if ((int)lpProcName & 0xffff0000) {

//名称
int i = 0;
while (i < pExpDir->NumberOfNames) {

//获取名称地址
int nNameOff = (int)(*(DWORD*)(pNameTbl + i * 4) + (DWORD)hMod);

//字符串比较
if (((char*)nNameOff)[0] == 'G'&& ((char*)nNameOff)[1] == 'e'&& ((char*)nNameOff)[2] == 't'&&
((char*)nNameOff)[3] == 'P'&& ((char*)nNameOff)[4] == 'r'&& ((char*)nNameOff)[5] == 'o'&&
((char*)nNameOff)[6] == 'c'&& ((char*)nNameOff)[7] == 'A'&& ((char*)nNameOff)[8] == 'd'&&
((char*)nNameOff)[9] == 'd'&& ((char*)nNameOff)[10] == 'r'&& ((char*)nNameOff)[11] == 'e'&&
((char*)nNameOff)[12] == 's'&& ((char*)nNameOff)[13] == 's') {

//找到了, 从导出序号表取出函数地址下标
int nOrdinal = *(WORD*)(pOrdTbl + i * 2);

//从导出地址表,下标寻址,获取导出函数地址
int nFuncAddr = *(DWORD*)(pAddrTbl + nOrdinal * 4);



//不是转发
nFuncAddr += (int)hMod;




//返回地址
if (nFuncAddr != NULL) {

return (FARPROC)nFuncAddr;
}
}

i++;

}
}

else {

//序号
int nOrdinal = (DWORD)lpProcName - pExpDir->Base;

//从导出地址表,下标寻址,获取导出函数地址
int nFuncAddr = *(DWORD*)(pAddrTbl + nOrdinal * 4);

//返回地址
if (nFuncAddr != NULL) {

return (FARPROC)(nFuncAddr + (DWORD)hMod);
}

}


return 0;
}

有了GetProcAddress函数地址和kernel32的基址,同理就能拿到LoadLibrary函数地址了。(注意定义字符串变量时,用单个字符一个一个排列,在汇编里面看就是db出来的,否则字符串会有一个常量区地址,影响shellcode的通用性)

char szLoadLibrary[] = { 'L', 'o','a', 'd', 'L', 'i', 'b', 'r', 'a', 'r', 'y', 'A', '\0' };
pEnv->pfnLoadLibraryA = (PFN_LoadLibraryA)pEnv->pfnGetProcAddress(hKer, szLoadLibrary);

2.有了LoadLibrary和GetProcAddress,就可以使用任何库函数了,解压缩便是小菜一碟。

//有了LoadLibrary和GetProcAddress,就可以使用任意函数了
//获取解压缩相关函数

char szCab[] = { 'C','a','b','i','n','e','t', '\0' };
HMODULE hCab = pEnv->pfnLoadLibraryA(szCab);

char szCreateDecompressor[] = { 'C','r','e','a','t','e','D','e','c','o','m','p','r','e','s','s','o','r', '\0' };
pEnv->pfnCreateDecompressor = (PFN_CreateDecompressor)pEnv->pfnGetProcAddress(hCab, szCreateDecompressor);

char szDecompress[] = { 'D','e','c','o','m','p','r','e','s','s', '\0' };
pEnv->pfnDecompress = (PFN_Decompress)pEnv->pfnGetProcAddress(hCab, szDecompress);

char szVirtualAlloc[] = { 'V','i','r','t','u','a','l','A','l','l','o','c', '\0' };
pEnv->pfnVirtualAlloc = (PFN_VirtualAlloc)pEnv->pfnGetProcAddress(hKer, szVirtualAlloc);

char szVirtualProtect[] = { 'V','i','r','t','u','a','l','P','r','o','t','e','c','t','\0' };
pEnv->pfnVirtualProtect = (PFN_VirtualProtect)pEnv->pfnGetProcAddress(hKer, szVirtualProtect);


//解压缩

LPBYTE pPEBuff = (LPBYTE)env.pfnVirtualAlloc(NULL, dwDeComSize, MEM_COMMIT, PAGE_READWRITE);

DECOMPRESSOR_HANDLE hDecompressor;
BOOL bSuccess = env.pfnCreateDecompressor(
COMPRESS_ALGORITHM_XPRESS_HUFF,
NULL,
&hDecompressor
);

DWORD dwDecompressedBufferSize = 0;
bSuccess = env.pfnDecompress(
hDecompressor,
pComData,
dwComSize,
pPEBuff,
dwDeComSize,
&dwDecompressedBufferSize
);

3.解压缩完毕,得到了原PE,接下来就是将原PE覆盖到现在的PE头+节表1的地方,同时还原节表头、导入表和重定位表,相当于LoadPE的功能了。

#define VirtualProtect pEnv->pfnVirtualProtect
DWORD MyLoadLibrary(LPBYTE pPEBuff, Environment* pEnv, LPBYTE pTableBuf, LPBYTE pMyImpBuf) {

DWORD dwImageBase;
HANDLE hFile;
HANDLE hFileMap;
LPVOID pPEBuf;
IMAGE_DOS_HEADER* pDosHdr;
IMAGE_NT_HEADERS* pNTHdr;
IMAGE_SECTION_HEADER* pSecHdr;
DWORD dwNumOfSecs;
IMAGE_IMPORT_DESCRIPTOR* pImpHdr;
DWORD dwSizeOfHeaders;
IMAGE_IMPORT_DESCRIPTOR hdrZeroImp;
HMODULE hDll;
DWORD dwOep;
DWORD dwOldProc;
IMAGE_BASE_RELOCATION* pReloc;
DWORD dwOfReloc;
DWORD dwOff;

//RtlZeroMemory(&hdrZeroImp, sizeof(IMAGE_IMPORT_DESCRIPTOR));

pPEBuf = pPEBuff;

//解析
//dos 头
pDosHdr = (IMAGE_DOS_HEADER*)pPEBuf;

//nt头
pNTHdr = (IMAGE_NT_HEADERS*)(pDosHdr->e_lfanew + (DWORD)pPEBuf);

//还原节表
DWORD nSecNum = *(DWORD*)pTableBuf;
mymemcpy((void*)((DWORD)&pNTHdr->OptionalHeader + pNTHdr->FileHeader.SizeOfOptionalHeader),
pTableBuf + 4, nSecNum * 40);

//还原导入表
mymemcpy(&(pNTHdr->OptionalHeader.DataDirectory[1].VirtualAddress),
pTableBuf + 4 + nSecNum * 40, 4);
mymemcpy(&(pNTHdr->OptionalHeader.DataDirectory[1].Size),
pTableBuf + 4 + nSecNum * 40 + 4, 4);

//还原重定位表
mymemcpy(&(pNTHdr->OptionalHeader.DataDirectory[5].VirtualAddress),
pTableBuf + 4 + nSecNum * 40 + 4 + 4, 4);
mymemcpy(&(pNTHdr->OptionalHeader.DataDirectory[5].Size),
pTableBuf + 4 + nSecNum * 40 + 4 + 4 + 4, 4);

//选项头信息
dwSizeOfHeaders = pNTHdr->OptionalHeader.SizeOfHeaders;


//自己的模块基址
dwImageBase = (DWORD)GetModuleBase();

dwOff = dwImageBase - pNTHdr->OptionalHeader.ImageBase; //新旧ImageBase的偏移差

dwOep = pNTHdr->OptionalHeader.AddressOfEntryPoint + dwImageBase;
//节表
dwNumOfSecs = pNTHdr->FileHeader.NumberOfSections;
pSecHdr = (IMAGE_SECTION_HEADER*)((DWORD)&pNTHdr->OptionalHeader + pNTHdr->FileHeader.SizeOfOptionalHeader);




//拷贝PE头
VirtualProtect((LPVOID)dwImageBase, pNTHdr->OptionalHeader.SizeOfHeaders, PAGE_EXECUTE_READWRITE, &dwOldProc);
mymemcpy((void*)dwImageBase, pPEBuf, dwSizeOfHeaders);
VirtualProtect((LPVOID)dwImageBase, pNTHdr->OptionalHeader.SizeOfHeaders, dwOldProc, &dwOldProc);


//按照节表,拷贝节区数据
int i = 0;
IMAGE_SECTION_HEADER* dwSecTmp = pSecHdr;
while (i < dwNumOfSecs) {

//目标
DWORD dwDstMem = dwImageBase;
dwDstMem += dwSecTmp->VirtualAddress;

//源
DWORD dwSrcFile = (DWORD)pPEBuf + dwSecTmp->PointerToRawData;

//拷贝
VirtualProtect((LPVOID)dwDstMem, dwSecTmp->SizeOfRawData, PAGE_EXECUTE_READWRITE, &dwOldProc);
mymemcpy((void*)dwDstMem, (void*)dwSrcFile, dwSecTmp->SizeOfRawData);
VirtualProtect((LPVOID)dwImageBase, pNTHdr->OptionalHeader.SizeOfHeaders, dwOldProc, &dwOldProc);

i++;
dwSecTmp = (IMAGE_SECTION_HEADER*)((char*)dwSecTmp + sizeof(IMAGE_SECTION_HEADER));
}


//获取导入表
if (pNTHdr->OptionalHeader.DataDirectory[IMAGE_DIRECTORY_ENTRY_IMPORT].VirtualAddress != 0) {

pImpHdr = (IMAGE_IMPORT_DESCRIPTOR*)(dwImageBase + pNTHdr->OptionalHeader.DataDirectory[IMAGE_DIRECTORY_ENTRY_IMPORT].VirtualAddress);


//处理导入表
IMAGE_IMPORT_DESCRIPTOR* pImpHdrTmp = pImpHdr;
DWORD dwNum = 0;
int nImpNum = 0;

while (true) {

//判断结束,全0项结束
if (memcmp(pImpHdrTmp, &hdrZeroImp, sizeof(IMAGE_IMPORT_DESCRIPTOR)) == 0) {

break;
}

//判断字段, 为空则结束
if (pImpHdrTmp->Name == NULL || pImpHdrTmp->FirstThunk == NULL) {

break;
}

//加载dll
hDll = pEnv->pfnLoadLibraryA((LPCSTR)(dwImageBase + pImpHdrTmp->Name));

//获取导入地址表, IAT
DWORD dwIAT = pImpHdrTmp->FirstThunk + dwImageBase;
DWORD dwINT = dwIAT;
//获取导入名称表, INT
if (pImpHdrTmp->OriginalFirstThunk != NULL) {

dwINT = pImpHdrTmp->OriginalFirstThunk + dwImageBase;
}

//遍历导入名称表
while (*(DWORD*)(dwINT) != 0) {

if ((*(DWORD*)pImpHdrTmp) >> 31) {

//序号导入, 获取序号
dwNum = *(DWORD*)pImpHdrTmp;
dwNum = (dwNum << 16) >> 16;

}
else {

//名称导入
dwNum = *(DWORD*)pImpHdrTmp;
dwNum += dwImageBase;
dwNum += 2;

}

//获取函数地址后,先不要把地址直接写入IAT
//而是先将.imp节地址写入IAT(每16个字节写一次)
//在.imp节里写代码指令push 函数地址 retn
//如果函数名是_acmdln,那么这里就不要混淆导入表
if (((LPCSTR)((*(DWORD*)(dwINT)) + dwImageBase + 2))[0] == '_' && ((LPCSTR)((*(DWORD*)(dwINT)) + dwImageBase + 2))[1] == 'a' &&
((LPCSTR)((*(DWORD*)(dwINT)) + dwImageBase + 2))[2] == 'c' && ((LPCSTR)((*(DWORD*)(dwINT)) + dwImageBase + 2))[3] == 'm' &&
((LPCSTR)((*(DWORD*)(dwINT)) + dwImageBase + 2))[4] == 'd' && ((LPCSTR)((*(DWORD*)(dwINT)) + dwImageBase + 2))[5] == 'l' &&
((LPCSTR)((*(DWORD*)(dwINT)) + dwImageBase + 2))[6] == 'n') {

*(DWORD*)dwIAT = (DWORD)pEnv->pfnGetProcAddress(hDll, (LPCSTR)((*(DWORD*)(dwINT)) + dwImageBase + 2));
}
else {

DWORD dwMyAddr = (DWORD)pMyImpBuf + nImpNum * 0x10;
DWORD dwFuncAddr = (DWORD)pEnv->pfnGetProcAddress(hDll, (LPCSTR)((*(DWORD*)(dwINT)) + dwImageBase + 2));
*(DWORD*)dwIAT = dwMyAddr;
*(BYTE*)dwMyAddr = 0x68; //push
*(DWORD*)(dwMyAddr + 1) = dwFuncAddr; //真实函数地址
*(BYTE*)(dwMyAddr + 5) = 0xC3; //retn
}


dwIAT += 4;
dwINT += 4;
nImpNum++;

}


pImpHdrTmp = (IMAGE_IMPORT_DESCRIPTOR*)((char*)pImpHdrTmp + sizeof(IMAGE_IMPORT_DESCRIPTOR));
}
}

if (pNTHdr->OptionalHeader.DataDirectory[5].VirtualAddress != 0) {

//定位重定位表
pReloc = (IMAGE_BASE_RELOCATION*)(pNTHdr->OptionalHeader.DataDirectory[5].VirtualAddress + dwImageBase);
dwOfReloc = pNTHdr->OptionalHeader.DataDirectory[5].Size;


int nSize = 0;

while (nSize < dwOfReloc) {

//数组首地址
int nOff = (DWORD)pReloc + 8;

//数组元素个数
int nCnt = (pReloc->SizeOfBlock - 8) >> 1;

//遍历数组
int j = 0;
while (j < nCnt) {

//取出一项
int nDataOff = *(WORD*)(nOff + j * 2);

//判断是否是有效重定位项
if (nDataOff & 0x00003000) {

//修正
nDataOff = nDataOff & 0x0fff; //页偏移
nDataOff = nDataOff + pReloc->VirtualAddress;
nDataOff = nDataOff + dwImageBase;

*(int*)nDataOff = *(int*)nDataOff + dwOff;
}

j++;
}

//处理下一个分页
nSize += pReloc->SizeOfBlock;
pReloc = (IMAGE_BASE_RELOCATION*)((char*)pReloc + pReloc->SizeOfBlock);

}
}



return dwOep;
}

这里重点要介绍的,就是还原导入表的过程,也是整篇文章的核心主题,加点“料”。我在遍历还原导入表时,并没有直接将API的地址填入到IAT里,而是将节表5的地址,从起始位置开始,每隔16个字节,将地址填入到IAT里,然后在对应的节表5地址上填入push 真实函数地址 + retn的汇编指令。这样一来,原PE程序运行调用API时,就会跳到节表5里面,再从节表5里面跳到真实API地址,直接干掉了x64dbg的脱壳导入表自动修复功能。

//获取函数地址后,先不要把地址直接写入IAT
//而是先将.imp节地址写入IAT(每16个字节写一次)
//在.imp节里写代码指令push 函数地址 retn
//如果函数名是_acmdln,那么这里就不要混淆导入表
if (((LPCSTR)((*(DWORD*)(dwINT)) + dwImageBase + 2))[0] == '_' && ((LPCSTR)((*(DWORD*)(dwINT)) + dwImageBase + 2))[1] == 'a' &&
((LPCSTR)((*(DWORD*)(dwINT)) + dwImageBase + 2))[2] == 'c' && ((LPCSTR)((*(DWORD*)(dwINT)) + dwImageBase + 2))[3] == 'm' &&
((LPCSTR)((*(DWORD*)(dwINT)) + dwImageBase + 2))[4] == 'd' && ((LPCSTR)((*(DWORD*)(dwINT)) + dwImageBase + 2))[5] == 'l' &&
((LPCSTR)((*(DWORD*)(dwINT)) + dwImageBase + 2))[6] == 'n') {

*(DWORD*)dwIAT = (DWORD)pEnv->pfnGetProcAddress(hDll, (LPCSTR)((*(DWORD*)(dwINT)) + dwImageBase + 2));
}
else {

DWORD dwMyAddr = (DWORD)pMyImpBuf + nImpNum * 0x10;
DWORD dwFuncAddr = (DWORD)pEnv->pfnGetProcAddress(hDll, (LPCSTR)((*(DWORD*)(dwINT)) + dwImageBase + 2));
*(DWORD*)dwIAT = dwMyAddr;
*(BYTE*)dwMyAddr = 0x68; //push
*(DWORD*)(dwMyAddr + 1) = dwFuncAddr; //真实函数地址
*(BYTE*)(dwMyAddr + 5) = 0xC3; //retn
}

总结

最后来看看效果,对扫雷进行加壳,加壳后的程序可以正常运行。

先用x64找到真实入口点,进行一波dump操作。

dump后无法直接运行。

然后去x64里使用自动搜索修复导入表的功能,可以看到,IAT这里存放的压根就不是真实API的地址,所以x64也无法识别出来。

搞定!

看雪ID:橘喵Cat

http://bbs.pediy.com/user-home-940656.htm

*本文由看雪论坛 橘喵Cat 原创,转载请注明来自看雪社区

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