TROJ_CRYPTOWALL.F

January 16, 2015
 Analysis by: Jimelle Monteser
 ALIASES:

Trojan horse Ransomer.DMI (AVG), Win32/Filecoder.CO trojan (NOD32)

 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 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 deletes the initially executed copy of itself.

  TECHNICAL DETAILS

File Size:

153,600 bytes

File Type:

EXE

Memory Resident:

Yes

Initial Samples Received Date:

10 Jun 2014

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 copies of itself into the affected system:

  • %System Root%\239e37e\239e37e.exe
  • %Application Data%\239e37e.exe
  • %User Startup%\239e37e.exe

(Note: %System Root% is the Windows root folder, where it usually is C:\ on all Windows operating system versions.. %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.. %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:

  • {File path of encrypted files}\DECRYPT_INSTRUCTION.HTML
  • {File path of encrypted files}\DECRYPT_INSTRUCTION.TXT
  • {File path of encrypted files}\DECRYPT_INSTRUCTION.URL

It creates the following folders:

  • %System Root%\239e37e

(Note: %System Root% is the Windows root folder, where it usually is C:\ on all Windows operating system versions.)

Other System Modifications

This Trojan adds the following registry keys:

HKEY_CURRENT_USER\Software\{random}

HKEY_CURRENT_USER\Software\{random}\
CRYPTLIST

It adds the following registry entries:

HKEY_CURRENT_USER\Software\{random}
1 = "{hex value}"

HKEY_CURRENT_USER\Software\{random}
2 = "{contents of DECRYPT_INSTRUCTION.TXT}"

HKEY_CURRENT_USER\Software\{random}
3 = "{contents of DECRYPT_INSTRUCTION.HTML}"

HKEY_CURRENT_USER\Software\{random}
4 = "?[DEFAULT] BASEURL=https://kpai7ycr7jxqkilp.tor2www.com/68s4 [InternetShortcut] URL=https://kpai7ycr7jxqkilp.tor2www.com/68s4"

HKEY_CURRENT_USER\Software\{random}\
CRYPTLIST
{file path of encrypted file} = "{random}"

Other Details

This Trojan connects to the following possibly malicious URL:

  • {BLOCKED}ntima.com
  • http://{BLOCKED}r7jxqkilp.tor2www.com:443

It deletes the initially executed copy of itself

NOTES:

It may encrypt files found on the system's hard drive.

  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

Restart in Safe Mode

[ Learn More ]

Step 3

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
    • {random}

Step 4

Search and delete these folders

[ 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%\239e37e

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.
  • {file path of encrypted files}\DECRYPT_INSTRUCTION.HTML
  • {file path of encrypted files}\DECRYPT_INSTRUCTION.TXT
  • {file path of encrypted files}\DECRYPT_INSTRUCTION.URL

Step 6

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