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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。
[出自:jiwo.org]
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。
