Analysis by: Pearl Charlaine Espejo

ALIASES:

Trojan.CryptoLocker (Malwarebytes); Win32/Filecoder.EM (ESET-NOD32); Trojan-Ransom.Win32.Bitman.ml (Kaspersky); W32/Bitman.EM!tr (Fortinet)

 PLATFORM:

Windows

 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, Dropped by other malware

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 modifies the Internet Explorer Zone Settings.

It connects to certain websites to send and receive information. It deletes the initially executed copy of itself.

  TECHNICAL DETAILS

File Size: 401,408 bytes
Memory Resident: Yes
Initial Samples Received Date: 13 May 2015
Payload: Encrypts files, Changes desktop wallpaper, Connects to URLs/IPs, Deletes files

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 7 characters}.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 - Contains the list of encrypted files.
  • %Desktop%\Save_Files - Shortcut file pointing to the dropped copy
  • %Application Data%\storage.bin
  • %Desktop%\HELP_RESTORE_FILES.txt
  • %Desktop%\HELP_RESTORE_FILES.bmp
  • %User Profile%\My Documents\RECOVERY_FILE.TXT

(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.. %User Profile% is the current user's profile folder, which is usually C:\Documents and Settings\{user name} on Windows 2000, XP, and Server 2003, or C:\Users\{user name} on Windows Vista and 7.)

It adds the following mutexes to ensure that only one of its copies runs at any one time:

  • safsdfasdfwrtqr15

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
AVrSvc = "%Application Data%\{Random 7 characters}.exe"

HKEY_CURRENT_USER\SOFTWARE\Microsoft\
Windows\CurrentVersion\Run
AVrSvc = "%Application Data%\{Random 7 characters}.exe"

Other System Modifications

This Trojan adds the following registry keys:

HKEY_CURRENT_USER\Software\Microsoft\
Windows\CurrentVersion\Settings\
storage

It adds the following registry entries:

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

It 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 Preference}.)

HKEY_CURRENT_USER\Control Panel\Desktop
TileWallpaper = "0"

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

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

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

Process Termination

This Trojan terminates processes or services that contain any of the following strings if found running in the affected system's memory:

  • taskmgr
  • procexp
  • regedit
  • msconfig
  • cmd.exe

Web Browser Home Page and Search Page Modification

This Trojan modifies the Internet Explorer Zone Settings.

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 website to send and receive information:

  • http://24u4jf7s4regu6hn.{BLOCKED}kjc38.com
  • http://24u4jf7s4regu6hn.{BLOCKED}s4we39.com
  • http://iq3ahijcfeont3xx.{BLOCKED}s4we39.com
  • http://24u4jf7s4regu6hn.{BLOCKED}b.{BLOCKED}gie.de:443
  • https://iq3ahijcfeont3xx.{BLOCKED}b.{BLOCKED}gie.de:443
  • http://24u4jf7s4regu6hn.{BLOCKED}b.org:443

It deletes the initially executed copy of itself

NOTES:

This Trojan deletes the Zone.Identifier NTFS stream to remove the downloaded files history.

It encrypt files with the following extensions in all folders found in the physical drives and appends .exx as the new file extension of the encrypted files:

  • 3fr
  • 7z
  • accdb
  • ai
  • apk
  • arch00
  • arw
  • asset
  • avi
  • bar
  • bay
  • bc6
  • bc7
  • big
  • bik
  • bkf
  • bkp
  • blob
  • bsa
  • cas
  • cdr
  • cer
  • cfr
  • cr2
  • crt
  • crw
  • css
  • csv
  • d3dbsp
  • das
  • dazip
  • db0
  • dba
  • dbf
  • dcr
  • der
  • desc
  • dmp
  • dng
  • doc
  • docm
  • docx
  • dwg
  • dxg
  • epk
  • eps
  • erf
  • esm
  • ff
  • flv
  • forge
  • fos
  • fpk
  • fsh
  • gdb
  • gho
  • hkdb
  • hkx
  • hplg
  • hvpl
  • ibank
  • icxs
  • indd
  • itdb
  • itl
  • itm
  • iwd
  • iwi
  • jpe
  • jpeg
  • jpg
  • js
  • kdb
  • kdc
  • kf
  • layout
  • lbf
  • litemod
  • lrf
  • ltx
  • lvl
  • m2
  • m3u
  • m4a
  • map
  • mcmeta
  • mdb
  • mdbackup
  • mddata
  • mdf
  • mef
  • menu
  • mlx
  • mov
  • mp4
  • mpqge
  • mrwref
  • ncf
  • nrw
  • ntl
  • odb
  • odc
  • odm
  • odp
  • ods
  • odt
  • orf
  • p12
  • p7b
  • p7c
  • pak
  • pdd
  • pdf
  • pef
  • pem
  • pfx
  • pkpass
  • png
  • ppt
  • pptm
  • pptx
  • psd
  • psk
  • pst
  • ptx
  • py
  • qdf
  • qic
  • r3d
  • raf
  • rar
  • raw
  • rb
  • re4
  • rgss3a
  • rim
  • rofl
  • rtf
  • rw2
  • rwl
  • sav
  • sb
  • sid
  • sidd
  • sidn
  • sie
  • sis
  • slm
  • snx
  • sql
  • sr2
  • srf
  • srw
  • sum
  • svg
  • syncdb
  • t12
  • t13
  • tax
  • tor
  • txt
  • upk
  • vcf
  • vdf
  • vfs0
  • vpk
  • vpp_pc
  • vtf
  • w3x
  • wallet
  • wb2
  • wma
  • wmo
  • wmv
  • wotreplay
  • wpd
  • wps
  • x3f
  • xf
  • xlk
  • xls
  • xlsb
  • xlsm
  • xlsx
  • xxx
  • zip
  • ztmp

It drops its ransom note HELP_RESTORE_FILES_{random characters}.TXT in all folders where files are encrypted.

It deletes shadow copies by executing the following command:

vssadmin.exe delete shadows /all /Quiet

It sets the system's desktop wallpaper to the following:

It demands payment for using its decryption service:

  SOLUTION

Minimum Scan Engine: 9.750
FIRST VSAPI PATTERN FILE: 11.670.07
FIRST VSAPI PATTERN DATE: 14 May 2015
VSAPI OPR PATTERN File: 11.671.00
VSAPI OPR PATTERN Date: 15 May 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
    • AVrSvc = "%Application Data%\{Random 7 characters}.exe"
  • In HKEY_CURRENT_USER\SOFTWARE\Microsoft\Windows\CurrentVersion\Run
    • AVrSvc = "%Application Data%\{Random 7 characters}.exe"

Step 5

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_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Settings
    • storage

Step 6

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%\log.html
  • %Application Data%\storage.bin
  • %Desktop%\Save_Files
  • %Desktop%\HELP_TO_SAVE_FILES.bmp
  • %Desktop%\HELP_TO_SAVE_FILES.txt
  • %User Profile%\My Documents\RECOVERY_FILE.TXT
  • HELP_RESTORE_FILES_{random characters}.TXT

Step 7

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 Preference}
  • In HKEY_CURRENT_USER\Control Panel\Desktop
    • From: TileWallpaper = "0"
      To: TileWallpaper = {User Preference}
  • In HKEY_CURRENT_USER\Control Panel\Desktop
    • From: Wallpaper = "%Desktop%\HELP_TO_SAVE_FILES.bmp"
      To: Wallpaper = {User Preference}

Step 8

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