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TROJ_CRYPTESLA.XXQH

May 09, 2015
 Analysis by: Miguel Carlo Ang
 ALIASES:

Trojan:Win32/Dynamer!ac(Microsoft);Trojan/Win32.Tescrypt(AhnLab-V3);Trojan-Ransom.Win32.Bitman.lr(Kaspersky)

 PLATFORM:

Windows

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

  • Threat Type: Trojan

  • Destructiveness: No

  • Encrypted:

  • In the wild: Yes

  OVERVIEW

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:

260,608 bytes

File Type:

EXE

Initial Samples Received Date:

09 May 2015

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 copies of itself into the affected system:

  • %AppDataLocal%\{random 7 character}.exe

(Note: %AppDataLocal% is the Application Data folder found in Local Settings, where it is usually C:\Documents and Settings\{user name}\Local Settings\Application Data on Windows 2000, Windows Server 2003, and Windows XP (32- and 64-bit); C:\Users\{user name}\AppData\Local on Windows Vista (32- and 64-bit), Windows 7 (32- and 64-bit), Windows 8 (32- and 64-bit), Windows 8.1 (32- and 64-bit), Windows Server 2008, and Windows Server 2012.)

It drops the following files:

  • %AppDataLocal%\log.html
  • %AppDataLocal%\storage.bin
  • %Desktop%\Save_Files.lnk
  • %Desktop%\HELP_RESTORE_FILES.bmp
  • %Desktop%\HELP_RESTORE_FILES.txt
  • {folder of encrypted file}\HELP_RESTORE_FILES_{random}.TXT

(Note: %AppDataLocal% is the Application Data folder found in Local Settings, where it is usually C:\Documents and Settings\{user name}\Local Settings\Application Data on Windows 2000, Windows Server 2003, and Windows XP (32- and 64-bit); C:\Users\{user name}\AppData\Local on Windows Vista (32- and 64-bit), Windows 7 (32- and 64-bit), Windows 8 (32- and 64-bit), Windows 8.1 (32- and 64-bit), Windows Server 2008, and Windows Server 2012.. %Desktop% is the desktop folder, where it usually is C:\Documents and Settings\{user name}\Desktop in Windows 2000, Windows Server 2003, and Windows XP (32- and 64-bit); C:\Users\{user name}\Desktop in Windows Vista (32- and 64-bit), Windows 7 (32- and 64-bit), Windows 8 (32- and 64-bit), Windows 8.1 (32- and 64-bit), Windows Server 2008, and Windows Server 2012.)

Autostart Technique

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

HKEY_CURRENT_USER\Software\Microsoft\
Windows\CurrentVersion\Run
AVrSvc = "%AppDataLocal%\{random 7 character}.exe"

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\
Windows\CurrentVersion\Run
AVrSvc = "%AppDataLocal%\{random 7 character}.exe"

Other System Modifications

This Trojan adds the following registry entries:

HKEY_CURRENT_USER\Software\Microsoft\
Windows\CurrentVersion\Explorer\
Advanced
Start_ShowNetPlaces_ShouldShow = 41

HKEY_CURRENT_USER\Software\Microsoft\
Windows\CurrentVersion\Settings\
storage
data = {data}

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\
Windows\CurrentVersion\policies\
system
EnableLinkedConnections = 1

HKEY_CURRENT_USER\Control Panel\Desktop
Wallpaper = "%Desktop%\HELP_RESTORE_FILES.bmp"

It modifies the following registry entries:

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\
Windows\CurrentVersion\BITS
StateIndex = 0

(Note: The default value data of the said registry entry is 1.)

Other Details

This Trojan connects to the following possibly malicious URL:

  • http://{BLOCKED}.io/ip
  • http://{BLOCKED}7s4regu6hn.{BLOCKED}gis35.com/ping.php?U3ViamVjdD1QaW5nJmtleT03RTdCRTY5NjQ2MkFDMDc3QjlGMkMwMkQzQ0ZEODIxRkJDM0NENTVCRENDOERBRUNBRkJGOTYxNTQ2OEYwRTc5JmFkZHI9MTRrbnFLa1cxODV3V0NESlJEdFpOeTlDcVVRRDRXYkMzeSZmaWxlcz0wJnNpemU9MCZ2ZXJzaW9uPTAuNC4wJk9TPTI2MDAmSUQ9NzYmc3ViaWQ9MCZnYXRlPUcwJmlzX2FkbWluPTEmaXNfNjQ9MCZpcD0xMjUuMjEyLjQzLjM4

It encrypts files with the following extensions:

  • {filename}.exx