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TROJ_CRYPWALL.G

September 05, 2014
 Analysis by: Rhena Inocencio
 ALIASES:

Ransom:Win32/Crowti.A (Microsoft)

 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:

  • In the wild: Yes

  OVERVIEW

Infection Channel:

Downloaded from the Internet, Dropped by other malware, Spammed via email


This Trojan arrives as an attachment to email messages spammed by other malware/grayware or malicious users. It 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:

163,840 bytes

File Type:

EXE

Memory Resident:

Yes

Initial Samples Received Date:

05 Sep 2014

Payload:

Steals information, Encrypts files, Compromises system security

Arrival Details

This Trojan arrives as an attachment to email messages spammed by other malware/grayware or malicious users.

It 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 adds the following processes:

  • explorer.exe
  • svchost.exe

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.)

It injects codes into the following process(es):

  • svchost.exe

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}

Information Theft

This Trojan gathers the following information on the affected computer:

  • Unique Identifier (UID)

Other Details

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

  • http://{BLOCKED}enkogitler.com/{random alphanumeric characters}
  • http://{BLOCKED}uvua.com/{random alphanumeric characters}
  • http://{BLOCKED}forua.com/{random alphanumeric characters}
  • http://{BLOCKED}hgitler.com/{random alphanumeric characters}
  • http://{BLOCKED}ayswar.com/{random alphanumeric characters}

NOTES:

This Trojan receives the public key from its C&C server. It is uses the public key to encrypt user files. It encrypts database, Web, office, video, images, scripts, text, and other non-binary files.

It drops DECRYPT_INSTRUCTION.TXT, DECRYPT_INSTRUCTION.HTML, and DECRYPT_INSTRUCTION.URL to all folders after encryption. It opens the dropped file DECRYPT_INSTRUCTION.TXT which contains the ransom note.

  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

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

Step 4

Restart in Safe Mode

[ Learn More ]

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
    • {7characters from UID} = "%Application Data%\{7 characters from UID}.exe"

Step 6

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 7

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 8

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 9

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