TROJ_CRYPWALL.D

This CryptoWall ransomware can be downloaded from a supposedly Dropbox link found in a spammed message with voicemail.

To get a one-glance comprehensive view of the behavior of this Trojan, refer to the Threat Diagram shown below.

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.

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.

It may be downloaded from the following remote site(s):

• https://www.dropbox.com/{BLOCKED}l/{BLOCKED}0aCI6ICIiLCAidGVzdF9saW5rIjogZmFsc2UsICJzZXJ2ZXIiOiAiZGwuZHJvcGJveHVzZXJjb250ZW50LmNvbSIsICJpdGVtX2lkIjogbnVsbCwgImlzX2RpciI6IGZhbHNlLCAidGtleSI6ICI1MHhpbmZzNzYzYXpsM3YifQ/AAMN9nJxM2drNQsYQyYRtRw1e_0u5PNyEahGPaIbnZu3iA

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}\
CRYPTLIST

It adds the following registry entries:

HKEY_CURRENT_USER\Software\{UID}\
CRYPTLIST\{Path of encrypted file}
{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}welcome.com/{random alphanumeric characters}

NOTES:

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

It 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:

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

It demands payment for using decryption service: