TROJ_CRYPWALL.YM

 Analysis by: Al Victor de Leon

 ALIASES:

Ransom:Win32/Crowti (Microsoft), Trojan-Ransom.Win32.Cryptodef.ru (Kaspersky), Trojan-Ransom.Win32.Cryptodef (Ikarus), W32/Cryptodef.RU!tr (Fortinet), Gen:Variant.Graftor.148894 (BitDefender)

 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:

Dropped by other malware, Downloaded from the Internet

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 gathers certain information on the affected computer.

It connects to certain websites to send and receive information. However, as of this writing, the said sites are inaccessible. It deletes itself after execution.

  TECHNICAL DETAILS

File Size:

176,128 bytes

File Type:

EXE

Memory Resident:

Yes

Initial Samples Received Date:

30 Jul 2014

Payload:

Encrypts 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:

  • %System Root%\{7 characters from UID}\{7 characters from UID}.exe
  • %Application Data%\{7 characters from UID}.exe
  • %User Startup%\{7 characters from UID}.exe

(Note: %System Root% is the root folder, which is usually C:\. It is also where the operating system is located.. %Application Data% is the current user's Application Data folder, which is usually C:\Documents and Settings\{user name}\Application Data on Windows 2000, XP, and Server 2003, or C:\Users\{user name}\AppData\Roaming on Windows Vista and 7.. %User Startup% is the current user's Startup folder, which is usually C:\Windows\Profiles\{user name}\Start Menu\Programs\Startup on Windows 98 and ME, C:\WINNT\Profiles\{user name}\Start Menu\Programs\Startup on Windows NT, and C:\Documents and Settings\{User name}\Start Menu\Programs\Startup.)

It drops the following files:

  • %User Startup%\DECRYPT_INSTRUCTION.TXT
  • %User Startup%\DECRYPT_INSTRUCTION.HTML
  • %User Startup%\DECRYPT_INSTRUCTION.URL

(Note: %User Startup% is the current user's Startup folder, which is usually C:\Windows\Profiles\{user name}\Start Menu\Programs\Startup on Windows 98 and ME, C:\WINNT\Profiles\{user name}\Start Menu\Programs\Startup on Windows NT, and C:\Documents and Settings\{User name}\Start Menu\Programs\Startup.)

It drops and executes the following files:

  • %Desktop%\DECRYPT_INSTRUCTION.TXT
  • %Desktop%\DECRYPT_INSTRUCTION.HTML
  • %Desktop%\DECRYPT_INSTRUCTION.URL

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

It creates the following folders:

  • %System Root%\{7 characters from UID}

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

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
{6 characters from UID} = "%System Root%\{7 characters from UID}\{7 characters from UID}.exe"

HKEY_CURRENT_USER\Software\Microsoft\
Windows\CurrentVersion\Run
{7characters from UID} = "%Application Data%\{7 characters from UID}.exe"

HKEY_CURRENT_USER\Software\Microsoft\
Windows\CurrentVersion\RunOnce
*{5 characters from UID} = "%System Root%\{7 characters from UID}\{7 characters from UID}.exe"

HKEY_CURRENT_USER\Software\Microsoft\
Windows\CurrentVersion\RunOnce
*{6characters from UID} = "%Application Data%\{7 characters from UID}.exe"

Other System Modifications

This Trojan adds the following registry keys:

HKEY_CURRENT_USER\Software\{UID}\
{random key}

HKEY_CURRENT_USER\Software\{UID}

It adds the following registry entries:

HKEY_CURRENT_USER\Software\{UID}\
{random key}
{Path and File name of encrypted file} = "{hex values}"

It modifies the following registry entries:

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\
Windows NT\CurrentVersion\SystemRestore
DisableSR = "1"

(Note: The default value data of the said registry entry is 0.)

Information Theft

This Trojan gathers the following information on the affected computer:

  • Unique Identifier (UID)
  • Machine Screenshot

Other Details

This Trojan connects to the following website to send and receive information:

  • http://{BLOCKED}aultppc.com/{random value}

However, as of this writing, the said sites are inaccessible.

It deletes itself after execution.

NOTES:

This Trojan drops the following files in every directory after encryption:

  • DECRYPT_INSTRUCTION.HTML
  • DECRYPT_INSTRUCTION.TXT
  • DECRYPT_INSTRUCTION.URL

It encrypts database, web, Office, video, images, scripts, text, and other non-binary files.

It displays the following page for instructions on how to decrypt files:



It demands payment for using decryption service:

  SOLUTION

Minimum Scan Engine:

9.700

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 key

[ Learn More ]

=Important: Editing the Windows Registry incorrectly can lead to irreversible system malfunction. Please do this only if you know how to or you can seek your system administrator’s help. You may also check out this Microsoft article first before modifying your computer's registry.

  • In HKEY_CURRENT_USER\Software
    • {UID}

Step 5

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_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Run
    • {6 characters from UID} = "%System Root%\{7 characters from UID}\{7 characters from UID}.exe"
  • In HKEY_CURRENT_USER\Software\Microsoft\ Windows\CurrentVersion\Run
    • {7 characters from UID} = "%Application Data%\{7 characters from UID}.exe"
  • In HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\RunOnce
    • *{5 characters from UID} = "%System Root%\{7 characters from UID}\{7 characters from UID}.exe"
  • In HKEY_CURRENT_USER\Software\Microsoft\ Windows\CurrentVersion\RunOnce
    • *{6characters from UID} = "%Application Data%\{7 characters from UID}.exe"

Step 6

Restore these modified registry values

[ Learn More ]

Important:Editing the Windows Registry incorrectly can lead to irreversible system malfunction. Please do this only if you know how to or you can seek your system administrator's help. You may also check out this Microsoft article first before modifying your computer's registry.

  • In HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows NT\CurrentVersion\SystemRestore
    • From: DisableSR = "1"
      To: DisableSR = 0

Step 7

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.
  • DECRYPT_INSTRUCTION.HTML
  • DECRYPT_INSTRUCTION.TXT
  • DECRYPT_INSTRUCTION.URL

Step 8

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