RANSOM_CRYPTESLA.YUYAIG

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.

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 copies of itself into the affected system and executes them:

• %Windows%\{random filename}.exe (with Administrator Privileges)
• %My Documents%\{random filename}.exe (with non-Administrator Privileges)

  (Note: %My Documents% is C:\Users\{user name}\Documents on Windows Vista and above.)

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

It drops the following file(s)/component(s):

• %Desktop%\RECOVERY.HTM
• %Desktop%\RECOVERY.png
• %Desktop%\RECOVERY.TXT
• %User Profile%\Recovery+{random characters}.html
• %User Profile%\Recovery+{random characters}.png
• %User Profile%\Recovery+{random characters}.txt
• {Folders containing encrypted files}\Recovery+{random characters}.html
• {Folders containing encrypted files}\Recovery+{random characters}.png
• {Folders containing encrypted files}\Recovery+{random characters}.txt
• %My Documents%\recover_file_{random characters}.txt
• %My Documents%\{random filename 2}.exe - used to delete shadow copies

  (Note: %My Documents% is usually C:\Documents and Settings\{user name}\My Documents on Windows 2000, XP, and Server 2003, or C:\Users\{user name}\Documents on Windows Vista and 7.)

(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.. %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.)

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
{4 random characters}-{8 random characters} = "%Windows%\{random filename}.exe" (with Administrator Privileges)

HKEY_CURRENT_USER\Software\Microsoft\
Windows\CurrentVersion\Run
{4 random characters}-{8 random characters} = "%My Documents%\{random filename}.exe" (with non-Administrator Privileges)

Other System Modifications

This Trojan modifies the following file(s):

• It encrypts files and appends the extension .mp3 to them

It adds the following registry keys:

HKEY_CURRENT_USER\Software\xxxsys

HKEY_CURRENT_USER\Software\{Installation ID}

It adds the following registry entries as part of its installation routine:

HKEY_CURRENT_USER\Software\xxxsys
ID = {Installation ID}

Web Browser Home Page and Search Page Modification

This Trojan modifies the Internet Explorer Zone Settings.

Other Details

This Trojan connects to the following possibly malicious URL:

• http://{BLOCKED}group.com/plugins/bsts.php
• http://{BLOCKED}de.co.kr/board/common/bsts.php
• http://{BLOCKED}ndmarketing101.net/docs/cache/bsts.php
• http://{BLOCKED}anph.com/wp-content/uploads/bsts.php
• http://{BLOCKED}inslow.com/csys.php
• http://{BLOCKED}dress.pl/wp-content/themes/sketch/csys.php