BKDR_CUTWAIL.A

April 16, 2014
 ALIASES:

a variant of Win32/Kryptik.BZGH trojan (Eset)

 PLATFORM:

Windows 2000, Windows Server 2003, Windows XP (32-bit, 64-bit), Windows Vista (32-bit, 64-bit), Windows 7 (32-bit, 64-bit)

 OVERALL RISK RATING:
 DAMAGE POTENTIAL:
 DISTRIBUTION POTENTIAL:
 REPORTED INFECTION:
 INFORMATION EXPOSURE:

  • Threat Type: Backdoor

  • Destructiveness: No

  • Encrypted:

  • In the wild: Yes

  OVERVIEW

Infection Channel:

Downloaded from the Internet, Dropped by other malware

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

It executes commands from a remote malicious user, effectively compromising the affected system. It connects to a website to send and receive information.

It gathers certain information on the affected computer.

  TECHNICAL DETAILS

File Size:

76,288 bytes

File Type:

EXE

Memory Resident:

Yes

Initial Samples Received Date:

16 Apr 2014

Payload:

Compromises system security, Connects to URLs/IPs, Collects system information

Arrival Details

This backdoor 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 backdoor drops the following copies of itself into the affected system and executes them:

  • %User Profile%\{random}.exe
  • %System%\{random}.exe

(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.. %System% is the Windows system folder, which is usually C:\Windows\System32.)

Autostart Technique

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

HKEY_LOCAL_MACHINE\Software\Microsoft\
Windows\CurrentVersion\Run
{random} = "%System%\{random}.exe"

HKEY_CURRENT_USER\Software\Microsoft\
Windows\CurrentVersion\Run
{random} = "%User Profile%\{random}.exe"

Other System Modifications

This backdoor adds the following registry entries:

HKEY_LOCAL_MACHINE\Software\WinNTData
prx = "{Hex Values}"

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

HKEY_LOCAL_MACHINE\Software\WinNTData

Backdoor Routine

This backdoor executes the following commands from a remote malicious user:

  • Download and Execute File
  • Load Modules
  • Configure Proxy Settings
  • Execute Arbitrary Codes
  • Terminate Self

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

  • {BLOCKED}.{BLOCKED}.173.34:443
  • {BLOCKED}.{BLOCKED}.110.120:443
  • {BLOCKED}.{BLOCKED}.184.252:443
  • {BLOCKED}.{BLOCKED}.243.100:433
  • {BLOCKED}.{BLOCKED}.15.103:443
  • {BLOCKED}.{BLOCKED}.216.83:443
  • {BLOCKED}.{BLOCKED}.198.255:443

Information Theft

This backdoor gathers the following information on the affected computer:

  • System Bios
  • Video Bios
  • CPU
  • Product ID

  SOLUTION

Minimum Scan Engine:

9.700

FIRST VSAPI PATTERN FILE:

10.714.06

FIRST VSAPI PATTERN DATE:

08 Apr 2014

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

Scan your computer with your Trend Micro product and note files detected as BKDR_CUTWAIL.A

Step 3

Restart in Safe Mode

[ Learn More ]

Step 4

Delete this registry key

[ Learn More ]

Important: Editing the Windows Registry incorrectly can lead to irreversible system malfunction. Please do this step only if you know how or you can ask assistance from your system administrator. Else, check this Microsoft article first before modifying your computer's registry.

  • In HKEY_LOCAL_MACHINE\Software
    • WinNTData

Step 5

Delete this registry value

[ Learn More ]

Important: Editing the Windows Registry incorrectly can lead to irreversible system malfunction. Please do this step only if you know how or you can ask assistance from your system administrator. Else, check this Microsoft article first before modifying your computer's registry.

 
  • In HKEY_LOCAL_MACHINE\Software\Microsoft\Windows\CurrentVersion\Run
    • {random} = "%System%\{random}.exe"
  • In HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Run
    • {random} = "%User Profile%\{random}.exe"

Step 6

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