RANSOM_CRYPTESLA.YSIM

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 modifies the Internet Explorer Zone Settings.

It connects to certain websites to send and receive information. It deletes the initially executed copy of itself.

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 and executes the following files:

• %Application Data%\{5 random letters}-a.exe

(Note: %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.)

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
askjhfaskewrtewtertwert123 = %Application Data%\{5 random letters}-a.exe

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\
Windows\CurrentVersion\Run
askjhfaskewrtewtertwert123 = %Application Data%\{5 random letters}-a.exe

Other System Modifications

This Trojan adds the following registry keys:

HKEY_CURRENT_USER\Software\zsys

HKEY_CURRENT_USER\Software\{installation ID}

It adds the following registry entries:

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\
Windows\CurrentVersion\Policies\
System
EnabledLinkConnections = 1

HKEY_CURRENT_USER\Software\{installation ID}
data = {encryption information}

HKEY_CURRENT_USER\Software\zsys
ID = {installation ID}

Web Browser Home Page and Search Page Modification

This Trojan modifies the Internet Explorer Zone Settings.

Dropping Routine

This Trojan drops the following files:

• %User Profile%\Documents\recover_file_{random letters}.txt
• %Desktop%\howto_recover_file_{random letters}.txt
• %Desktop%\howto_recover_file_{random letters}.html
• %Desktop%\howto_recover_file_{random letters}.bmp

(Note: %User Profile% is the current user's profile folder, which is usually C:\Documents and Settings\{user name} on Windows 2000, XP, and Server 2003, or C:\Users\{user name} on Windows Vista and 7.. %Desktop% is the desktop folder, where it usually is C:\Documents and Settings\{user name}\Desktop in Windows 2000, Windows Server 2003, and Windows XP (32- and 64-bit); C:\Users\{user name}\Desktop in 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.)

Other Details

This Trojan connects to the following URL(s) to get the affected system's IP address:

• http://myexternalip.com/raw

It connects to the following website to send and receive information:

• http://{BLOCKED}control.com/exporterofgiftitems.com/wp-admin/misc.php?{data}
• http://{BLOCKED}cam.com/wp-content/themes/twentythirteen/misc.php?{data}
• http://{BLOCKED}hthaidieplonghong.com.vn/misc.php?{data}
• http://{BLOCKED}tfilma.com/modules/misc.php?{data}
• http://{BLOCKED}mfort.com/modules/misc.php?{data}
• http://{BLOCKED}nect.it/misc.php?{data}

It opens the following files:

• dropped %Desktop%\howto_recover_file_{random letters}.txt
• dropped %Desktop%\howto_recover_file_{random letters}.html
• dropped %Desktop%\howto_recover_file_{random letters}.bmp

(Note: %Desktop% is the desktop folder, where it usually is C:\Documents and Settings\{user name}\Desktop in Windows 2000, Windows Server 2003, and Windows XP (32- and 64-bit); C:\Users\{user name}\Desktop in 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.)

It deletes the initially executed copy of itself

NOTES:

This malware appends the extension .ccc to the file name of the encrypted files.

It drops howto_recover_file_{random letters}.html and howto_recover_file_{random letters}.txt to the folders where the files are encrypted.