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Threat Encyclopedia

TROJ_RANSOM.HUN

ANALYSIS BY

Mark Joseph Manahan


ALIASES:

Troj/KillProc-N (Sophos) ,Trojan:Win32/Twirlwind (Microsoft) ,Win32/LockScreen.BFK trojan (Eset) ,Trojan.Ransomcrypt (Symantec) ,Trojan.Win32.Generic!BT (Sunbelt)

PLATFORM:

Windows 2000, Windows Server 2003, Windows XP (32-bit, 64-bit), Windows Vista (32-bit, 64-bit), Windows 7 (32-bit, 64-bit)

OVERALL RISK RATING:
DAMAGE POTENTIAL:
DISTRIBUTION POTENTIAL:
REPORTED INFECTION:
INFORMATION EXPOSURE:

  • Threat Type:Trojan

  • Destructiveness:No

  • Encrypted: Yes

  • In the wild: Yes

OVERVIEW

Infection Channel:

Downloaded from the Internet


This ransomware variant targets users in Hungary. It locks users' computers and lists the encrypted file types. It also lists steps to unlock the files, along with the ransom amount.

To get a one-glance comprehensive view of the behavior of this Trojan, refer to the Threat Diagram shown below.

This Trojan arrives on a system as a file dropped by other malware or as a file downloaded unknowingly by users when visiting malicious sites.

TECHNICAL DETAILS

File Size:

582,144 bytes

File Type:

EXE

Memory Resident:

Yes

Initial Samples Received Date:

20 Feb 2014

Payload:

Terminates processes, Displays graphics/image

Arrival Details

This Trojan arrives on a system as a file dropped by other malware or as a file downloaded unknowingly by users when visiting malicious sites.

Installation

This Trojan drops the following files:

  • %System Root%\w.bmp

(Note: %System Root% is the root folder, which is usually C:\. It is also where the operating system is located.)

It drops the following file(s)/component(s):

  • %Windows%\system\cl32.dll

(Note: %Windows% is the Windows folder, which is usually C:\Windows.)

It drops the following copies of itself into the affected system:

  • %Windows%\system\csrss.exe

(Note: %Windows% is the Windows folder, which is usually C:\Windows.)

It adds the following processes:

  • iexplore.exe
        Launch http://szelvesz.2u.se/hun

Autostart Technique

This Trojan adds the following registry entries to enable its automatic execution at every system startup:

HKEY_LOCAL_MACHINE\Software\Microsoft\
Windows\CurrentVersion\Run
MS = "{Malware Path}\{Malware Filename}.exe}"

Other System Modifications

This Trojan adds the following registry keys:

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\
Windows NT\CurrentVersion\Image File Execution Options\
cmd.exe

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\
Windows NT\CurrentVersion\Image File Execution Options\
command.com

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\
Windows NT\CurrentVersion\Image File Execution Options\
dllhost.exe

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\
Windows NT\CurrentVersion\Image File Execution Options\
mbam.exe

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\
Windows NT\CurrentVersion\Image File Execution Options\
msconfig.exe

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\
Windows NT\CurrentVersion\Image File Execution Options\
regedit.exe

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\
Windows NT\CurrentVersion\Image File Execution Options\
rstrui.exe

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\
Windows NT\CurrentVersion\Image File Execution Options\
taskmgr.exe

Process Termination

This Trojan terminates the following processes if found running in the affected system's memory:

  • taskmgr.exe
  • msconfig.exe
  • rundll32.exe
  • cmd.exe
  • mbam.exe
  • rstrui.exe

Other Details

This Trojan encrypts files with the following extensions:

  • *.jpeg
  • *.jpg
  • *.doc
  • *.png
  • *.gif
  • *.mp3
  • *.mp4
  • *.wav
  • *.docx
  • *.rtf
  • *.txt
  • *.pps
  • *.ppt
  • *.pptx
  • *.m4a
  • *.mid
  • *.wmv
  • *.wma
  • *.mpg
  • *.mov
  • *.avi
  • *.3gp
  • *.psd
  • *.xls
  • *.xlxs
  • *.html
  • *.php
  • *.zip
  • *.rar
  • *.bak

It requires the existence of the following files to properly run:

  • {Malware Path}\CL32.dll

NOTES:

This Trojan creates the following registry entries to prevent execution of system and security tools:

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\
Windows NT\CurrentVersion\Image File Execution Options\{app name}
Debugger = "%System Root%\die.exe"

The variable {app name} may be any of the following:

  • cmd.exe
  • command.com
  • dllhost.exe
  • mbam.exe
  • msconfig.exe
  • regedit.exe
  • rstrui.exe
  • taskmgr.exe

It appends .ENC to encrpyted files. It locks the user's system and displays the following:

SOLUTION

Minimum Scan Engine:

9.700

FIRST VSAPI PATTERN FILE:

10.618.05

FIRST VSAPI PATTERN DATE:

20 Feb 2014

VSAPI OPR PATTERN File:

10.619.00

VSAPI OPR PATTERN Date:

20 Feb 2014

Step 1

Before doing any scans, Windows XP, Windows Vista, and Windows 7 users must disable System Restore to allow full scanning of their computers.

Step 2

Restart in Safe Mode

[ Learn More ]

Step 3

Delete this registry key

[ Learn More ]

Important: Editing the Windows Registry incorrectly can lead to irreversible system malfunction. Please do this step only if you know how or you can ask assistance from your system administrator. Else, check this Microsoft article first before modifying your computer's registry.


 
  • In HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows NT\CurrentVersion\Image File Execution Options
    • cmd.exe
  • In HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows NT\CurrentVersion\Image File Execution Options
    • command.com
  • In HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows NT\CurrentVersion\Image File Execution Options
    • dllhost.exe
  • In HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows NT\CurrentVersion\Image File Execution Options
    • mbam.exe
  • In HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows NT\CurrentVersion\Image File Execution Options
    • msconfig.exe
  • In HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows NT\CurrentVersion\Image File Execution Options
    • regedit.exe
  • In HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows NT\CurrentVersion\Image File Execution Options
    • rstrui.exe
  • In HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows NT\CurrentVersion\Image File Execution Options
    • taskmgr.exe

Step 4

Delete this registry value

[ Learn More ]

Important: Editing the Windows Registry incorrectly can lead to irreversible system malfunction. Please do this step only if you know how or you can ask assistance from your system administrator. Else, check this Microsoft article first before modifying your computer's registry.


  • In HKEY_LOCAL_MACHINE\Software\Microsoft\Windows\CurrentVersion\Run
    • MS = "{Malware Path}\{Malware Filename}.exe}"

Step 5

Search and delete this file

[ Learn More ]
There may be some files that are hidden. Please make sure you check the Search Hidden Files and Folders checkbox in the "More advanced options" option to include all hidden files and folders in the search result.
  • %System Root%\w.bmp

Step 6

Restart in normal mode and scan your computer with your Trend Micro product for files detected as TROJ_RANSOM.HUN. If the detected files have already been cleaned, deleted, or quarantined by your Trend Micro product, no further step is required. You may opt to simply delete the quarantined files. Please check this Knowledge Base page for more information.


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