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TROJ_CUTWAIL.YAC

May 19, 2014
 Analysis by: RonJay Kristoffer Caragay
 ALIASES:

TrojanDownloader:Win32/Cutwail.BF (Microsoft); Trojan.Win32.Cutwail.ctt (Kaspersky); Troj/Cutwail-BF(Sophos_lite); W32/Cutwail.CTT!tr(Fortinet)

 PLATFORM:

Windows 2000, Windows XP, Windows Server 2003

 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:

59,904 bytes

File Type:

EXE

Initial Samples Received Date:

08 May 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.

Autostart Technique

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

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\
Windows\CurrentVersion\Run
{random filename.exe} = "%System%\{random file name}.exe"

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

Other System Modifications

This Trojan adds the following registry keys:

HKEY_LOCAL_MACHINE\Software\WinNTData

HKEY_CURRENT_USER\Software\WinNTData

It adds the following registry entries:

HKEY_LOCAL_MACHINE\SOFTWARE\WinNTData
prx = "{hex values}"

HKEY_CURRENT_USER\Software\WinNTData
prx = "{hex values}"

Dropping Routine

This Trojan drops the following files:

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

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

Other Details

This Trojan deletes itself after execution.