Threat Level: green Handler on Duty: Remco Verhoef

SANS ISC: Reader Analysis: "Dynamic analysis technique to get decrypted KPOT Malware." SANS ISC InfoSec Forums

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Reader Analysis: "Dynamic analysis technique to get decrypted KPOT Malware."

Reader Vinnie shared his analysis of KPOT malware with us:

 

In a previous write up, I documented a PowerShell downloader (shown below) pushing KPOT malware. Since then, all of the files have been submitted to VirusTotal allowing for further analysis. This has also been recently documented by ISC Handler Didier Stevens (ISC Links below).
PowerShell Downloader:
 
ISC Links:
- https://isc.sans.edu/forums/diary/More+COVID19+Themed+Malware/25930/
- https://isc.sans.edu/forums/diary/KPOT+Deployed+via+AutoIt+Script/25934/

URLs from PowerShell Downloader:
hxxp://show1[.]website/OerAS.dat (Obfuscated AutoIt script, Base64 encoded as a certificate)
hxxp://show1[.]website/HeyaL.dat (AutoIt Interpreter) – Legitimate
hxxp://show1[.]website/iPYOy.dat (Encrypted KPOT Malware)

Excerpt from Base64 decoded AutoIt script(‘i8ek7’) showing obfuscation:


 
Decode function at the bottom of AutoIt script:


 
The string is split from ‘*’ and then each encoded character is subtracted from the number after the comma($integer) before being converted from Unicode.

Decoded sample:


 
All files necessary in the same folder ‘Temp’ – Windows 7 Virtual Machine:
 


Utilizing PowerShell to initiate infection chain:

Process chain showing ‘dllhost.exe’ process hollowing:
 CreateProcess: powershell.exe:2428 > "%UserProfile%\Downloads\Temp\r17mi.com i8ek7 "    
- [Child PID: 2452]
CreateProcess: r17mi.com:2452 > "%UserProfile%\Downloads\Temp\r17mi.com i8ek7 "    
- [Child PID: 2064]
CreateProcess: r17mi.com:2064 > "%WinDir%\SysWOW64\dllhost.exe"    
- [Child PID: 2244]
CreateProcess: dllhost.exe:2244 > "%WinDir%\system32\cmd.exe /c ping 127.0.0.1 && del %WinDir%\SysWOW64\dllhost.exe"    
- [Child PID: 536]
CreateProcess: cmd.exe:536 > "ping  127.0.0.1 "


“dllhost.exe” process dump via Task Manager:


String analysis via “strings” show command and control (C2) servers:

Extract executables via “foremost”:


The decrypted KPOT malware has the SHA256 Hash “3fd4aa339bdfee23684ff495d884aa842165e61af85fd09411abfd64b9780146” and VT score of 34/71.
https://www.virustotal.com/gui/file/3fd4aa339bdfee23684ff495d884aa842165e61af85fd09411abfd64b9780146/detection

Sampled VirusTotal signatures:

String analysis of KPOT malware via “FLOSS”:

Strings indicative of information stealers:

 

 

Didier Stevens
Senior handler
Microsoft MVP
blog.DidierStevens.com DidierStevensLabs.com

DidierStevens

451 Posts
ISC Handler

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