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TROJ_CRYPWALL.YB

October 21, 2014
 Analysis by: Francis Xavier Antazo
 ALIASES:

Trojan:Win32/Anaki.A (Microsoft); PWSZbot-FAEC!135C144CABB3 (McAfee); Trojan-Ransom.Win32.Cryptodef.bsk (Kaspersky); Troj/Ransom-ALZ (Sophos); Trojan.Win32.Generic!BT (Sunbelt); Trojan horse Inject2.AXKK (AVG)

 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 on a system as a file dropped by other malware or as a file downloaded unknowingly by users when visiting malicious sites.

It deletes itself after execution.

  TECHNICAL DETAILS

File Size:

321,536 bytes

File Type:

EXE

Memory Resident:

Yes

Initial Samples Received Date:

20 Oct 2014

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 files:

  • %Desktop%\DECRYPT_INSTRUCTION.HTML
  • %Desktop%\DECRYPT_INSTRUCTION.TXT
  • %Desktop%\DECRYPT_INSTRUCTION.URL

(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.)

Autostart Technique

This Trojan adds the following registry entries to enable its automatic execution at every system startup:

HKEY_CURRENT_USER\Software\(UID)\
{Random Key}
{path and file name of encrypted file} = "{Hex Values}"

HKEY_CURRENT_USER\Software\(UID)
{Random Entry} = "{Hex Values}"

HKEY_CURRENT_USER\Software\(UID)
{Random Entry} = "[DEFAULT]BASEURL=https://kpai7ycr7jxqkilp.torminater.com/{Random Letter 1}[InternetShortcut]URL=https://kpai7ycr7jxqkilp.torminater.com/{Random Letter 1}"

HKEY_CURRENT_USER\Software\Microsoft\
Windows\CurrentVersion\RunOnce
{Random Key} = "%System Root%\{random folder name}\{random folder name}.exe"

HKEY_CURRENT_USER\Software\Microsoft\
Windows\CurrentVersion\RunOnce
{random folder name} = "%Application Data%\{random folder name}.exe

HKEY_CURRENT_USER\Software\Microsoft\
Windows\CurrentVersion\Run
{random key} = "%System Root%\{random folder name}\{random folder name}.exe"

HKEY_CURRENT_USER\Software\Microsoft\
Windows\CurrentVersion\Run
{random folder name} = "%Application Data%\{random folder name}.exe"

It drops the following file(s) in the Windows User Startup folder to enable its automatic execution at every system startup:

  • %User Startup%\{random folder name}.exe

(Note: %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.)

Other System Modifications

This Trojan adds the following registry keys:

HKEY_CURRENT_USER\Software\(UID)

HKEY_CURRENT_USER\Software\(UID)\
{Random Key}

It modifies the following registry entries:

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\
Windows NT\CurrentVersion\SystemRestore
DisableSR = "1"

(Note: The default value data of the said registry entry is "0".)

Other Details

This Trojan connects to the following possibly malicious URL:

  • http://{BLOCKED}ntin.com
  • http://{BLOCKED}poster.com
  • http://{BLOCKED}tsp.com
  • http://{BLOCKED}y.com
  • http://{BLOCKED}nih.com

It deletes itself after execution.