TROJ_CRYPWALL.YN

 Analysis by: Vincent Martin Hermosura

 ALIASES:

Ransom:Win32/Crowti (Microsoft), RDN/Ransom!ej (Mcafee), Win32.Malware!Drop (Sunbelt), TR/FileCoder.CO.10 (Antivir), Trojan.GenericKD.1811994 (Bitdefender), W32/Filecoder.CO!tr (Fortinet), Trojan-Spy.Zbot (Ikarus), Win32/Filecoder.CO trojan (Esset), Trj/Chgt.D (Panda)

 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, 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 gathers certain information on the affected computer.

It connects to certain websites to send and receive information.

  TECHNICAL DETAILS

File Size:

147,968 bytes

File Type:

EXE

Memory Resident:

Yes

Initial Samples Received Date:

19 Aug 2014

Payload:

Steals information, Encrypts files, Compromises system security

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:

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

Other System Modifications

This Trojan adds the following registry keys:

HKEY_CURRENT_USER\Software\{UID}

HKEY_CURRENT_USER\Software\{UID}\
{UID}

It adds the following registry entries:

HKEY_CURRENT_USER\Software\{UID}\
{UID}
{Path and Filename of encrypted file} = ""

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}linkme.com/{random alphanumeric characters}

NOTES:

It drops DECRYPT_INSTRUCTION.TXT, DECRYPT_INSTRUCTION.HTML, and DECRYPT_INSTRUCTION.URL to all folders after encryption.

This Trojan encrypts Database, Web, Office, Video, Images, Scripts, Text and other non-binary files.

It opens the dropped file DECRYPT_INSTRUCTION.TXT which contains the ransom note:

  SOLUTION

Minimum Scan Engine:

9.700

VSAPI OPR PATTERN Date:

11 Jun 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

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

Scan your computer with your Trend Micro product and note files detected as TROJ_CRYPWALL.YN

Step 4

Restart in Safe Mode

[ Learn More ]

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
    • {UID}

Step 6

Search and delete this folder

[ Learn More ]
Please make sure you check the Search Hidden Files and Folders checkbox in the More advanced options option to include all hidden folders in the search result.
  • %System Root%\{random name}

Step 7

Search and delete these files

[ 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.
  • %Desktop%\DECRYPT_INSTRUCTION.TXT
  • %Desktop%\DECRYPT_INSTRUCTION.HTML
  • %Desktop%\DECRYPT_INSTRUCTION.URL
  • %User Startup%\DECRYPT_INSTRUCTION.TXT
  • %User Startup%\DECRYPT_INSTRUCTION.HTML
  • %User Startup%\DECRYPT_INSTRUCTION.URL
  • {Folder Path and Name}\DECRYPT_INSTRUCTION.TXT
  • {Folder Path and Name}\DECRYPT_INSTRUCTION.HTML
  • {Folder Path and Name}\DECRYPT_INSTRUCTION.URL

Step 8

Restart in normal mode and scan your computer with your Trend Micro product for files detected as TROJ_CRYPWALL.YN. 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 9

The following created files/folders/registry keys/registry entries cannot be identified by the user since there are no reference values in the created key. The only way it can be identified is by comparing the present system information with a backup. Note that the said components do not have to be deleted since it won't be harmful to the 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


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