Analysis by: Miguel Carlo Ang
 Modified by: David John Agni

ALIASES:

Ransom:Win32/Tescrypt.A (Microsoft); Win32/Filecoder.EM (ESET-NOD32); Trojan.Win32.Filecoder (Ikarus)

 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.

It deletes the initially executed copy of itself.

  TECHNICAL DETAILS

File Size: 192,512 bytes
File Type: EXE
Memory Resident: Yes
Initial Samples Received Date: 20 Mar 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 and executes them:

  • %Application Data%\{Random Filename}.exe

(Note: %Application Data% is the Application Data folder, where it usually is C:\Documents and Settings\{user name}\Application Data on Windows 2000, Windows Server 2003, and Windows XP (32- and 64-bit); C:\Users\{user name}\AppData\Roaming 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:

  • %Application Data%\log.html
  • %Desktop%\HELP_TO_SAVE_YOUR_FILES.bmp
  • %Desktop%\HELP_TO_SAVE_YOUR_FILES.txt
  • %Desktop%\CryptoLocker.lnk
  • %Application Data%\key.dat

(Note: %Application Data% is the Application Data folder, where it usually is C:\Documents and Settings\{user name}\Application Data on Windows 2000, Windows Server 2003, and Windows XP (32- and 64-bit); C:\Users\{user name}\AppData\Roaming 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_LOCAL_MACHINE\SOFTWARE\Microsoft\
Windows\CurrentVersion\Run
svv_e = "%Application Data%\{Random Filename}.exe"

Other System Modifications

This Trojan modifies the following registry entries:

HKEY_CURRENT_USER\Control Panel\Desktop
WallpaperStyle = "0"

(Note: The default value data of the said registry entry is {User Preferences}.)

HKEY_CURRENT_USER\Control Panel\Desktop
TileWallpaper = "0"

(Note: The default value data of the said registry entry is {User Preferences}.)

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

(Note: The default value data of the said registry entry is {User Preferences}.)

Other Details

This Trojan connects to the following URL(s) to get the affected system's IP address:

  • http://ipinfo.io/ip

It connects to the following possibly malicious URL:

  • http://{BLOCKED}7vlep5o.42kdb12.net/state1.php?
  • http://{BLOCKED}7vlep5o.42kjb11.net/state1.php?
  • http://{BLOCKED}7vlep5o.tor2web.blutmagie.de:443
  • http://{BLOCKED}7vlep5o.tor2web.fi:443

It renames encrypted files using the following names:

  • {original filename}.ecc

It does the following:

  • This Trojan encrypts the infected machine's personal files and demands payment for decryption service.

It deletes the initially executed copy of itself

  SOLUTION

Minimum Scan Engine: 9.750
FIRST VSAPI PATTERN FILE: 11.556.04
FIRST VSAPI PATTERN DATE: 19 Mar 2015
VSAPI OPR PATTERN File: 11.557.00
VSAPI OPR PATTERN Date: 20 Mar 2015

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

Note that not all files, folders, and registry keys and entries are installed on your computer during this malware's/spyware's/grayware's execution. This may be due to incomplete installation or other operating system conditions. If you do not find the same files/folders/registry information, please proceed to the next step.

Step 3

Restart in Safe Mode

[ Learn More ]

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
    • svv_e = "%Application Data%\{Random 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.
  • %Application Data%\key.dat
  • %Application Data%\log.html
  • %Desktop%\HELP_TO_SAVE_YOUR_FILES.bmp
  • %Desktop%\HELP_TO_SAVE_YOUR_FILES.txt
  • %Desktop%\CryptoLocker.lnk

Step 6

Restore this modified 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_CURRENT_USER\Control Panel\Desktop
    • From: WallpaperStyle = "0"
      To: WallpaperStyle = {User Preferences}
  • In HKEY_CURRENT_USER\Control Panel\Desktop
    • From: TileWallpaper = "0"
      To: TileWallpaper = {User Preferences}
  • In HKEY_CURRENT_USER\Control Panel\Desktop
    • From: Wallpaper = "%Desktop%\HELP_TO_SAVE_YOUR_FILES.bmp"
      To: Wallpaper = {User Preferences}

Step 7

Restart in normal mode and scan your computer with your Trend Micro product for files detected as TROJ_CRYPTESLA.J. 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.

Step 8

Scan your computer with your Trend Micro product to delete files detected as TROJ_CRYPTESLA.J. 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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