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TROJ_LLAC.FS

May 25, 2013
 ALIASES:

PWS-Zbot.gen.zy (McAfee); Trojan horse Dropper.Delf.5.BB (AVG)

 PLATFORM:

Windows 2000, Windows XP, Windows Server 2003

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

  • 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.

  TECHNICAL DETAILS

File Size:

100,352 bytes

File Type:

EXE

Memory Resident:

Yes

Initial Samples Received Date:

25 May 2013

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:

  • %Windows%\Yahoo..!\yahoo helper.exe

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

It creates the following folders:

  • %Windows%\Yahoo..!

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

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
HKLM = "%Windows%\Yahoo..!\yahoo helper.exe"

HKEY_CURRENT_USER\Software\Microsoft\
Windows\CurrentVersion\Run
HKCU = "%Windows%\Yahoo..!\yahoo helper.exe"

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\
Active Setup\Installed Components\{1D13U3N1-36Q2-5YON-827Q-6P44RM32N8PS}
StubPath = "%Windows%\Yahoo..!\yahoo helper.exe"

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\
Active Setup\Installed Components\{1D13U3N1-36Q2-5YON-827Q-6P44RM32N8PS}
StubPath = "%Windows%\Yahoo..!\yahoo helper.exe restart"

HKEY_CURRENT_USER\Software\Microsoft\
Windows\CurrentVersion\Run
YahOO = "%Windows%\Yahoo..!\yahoo helper.exe"

Other System Modifications

This Trojan adds the following registry keys:

HKEY_CURRENT_USER\SOFTWARE\XtremeRAT

HKEY_CURRENT_USER\SOFTWARE\Ckf1dsk7gs

HKEY_LOCAL_MACHINE\Software\Microsoft\
Active Setup\Installed Components\{1D13U3N1-36Q2-5YON-827Q-6P44RM32N8PS}

It adds the following registry entries:

HKEY_CURRENT_USER\Software\XtremeRAT
Mutex = "Ckf1dsk7gs"

HKEY_CURRENT_USER\Software\Ckf1dsk7gs
ServerStarted = "21/05/2013 23:03:18"

HKEY_CURRENT_USER\Software\Ckf1dsk7gs
ServerName = "%Windows%\Yahoo..!\yahoo helper.exe"

HKEY_CURRENT_USER\Software\Ckf1dsk7gs
InstalledServer = "%Windows%\Yahoo..!\yahoo helper.exe"

It modifies the following registry entries:

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\
DirectDraw\MostRecentApplication
Name = "svchost.exe"

(Note: The default value data of the said registry entry is iexplore.exe.)

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\
DirectDraw\MostRecentApplication
ID = "4117ed6"

(Note: The default value data of the said registry entry is 41107b81.)

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\
DirectDraw\MostRecentApplication
Name = "iexplore.exe"

(Note: The default value data of the said registry entry is iexplore.exe.)

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\
DirectDraw\MostRecentApplication
ID = "4117b81"

(Note: The default value data of the said registry entry is 41107b81.)

Dropping Routine

This Trojan drops the following files:

  • %User Temp%\x.html
  • %User Profile%\Windows\Ckf1dsk7gs.xtr
  • %User Profile%\Windows\Ckf1dsk7gs.cfg

(Note: %User Temp% is the current user's Temp folder, which is usually C:\Documents and Settings\{user name}\Local Settings\Temp on Windows 2000, XP, and Server 2003, or C:\Users\{user name}\AppData\Local\Temp on Windows Vista and 7.. %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.)

This report is generated via an automated analysis system.

  SOLUTION

Minimum Scan Engine:

9.300

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

Restart in Safe Mode

[ Learn More ]

Step 3

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_CURRENT_USER\SOFTWARE
    • XtremeRAT
  • In HKEY_CURRENT_USER\SOFTWARE
    • Ckf1dsk7gs
  • In HKEY_LOCAL_MACHINE\Software\Microsoft\Active Setup\Installed Components
    • {1D13U3N1-36Q2-5YON-827Q-6P44RM32N8PS}

Step 4

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
    • HKLM = "%Windows%\Yahoo..!\yahoo helper.exe"
  • In HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Run
    • HKCU = "%Windows%\Yahoo..!\yahoo helper.exe"
  • In HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Active Setup\Installed Components\{1D13U3N1-36Q2-5YON-827Q-6P44RM32N8PS}
    • StubPath = "%Windows%\Yahoo..!\yahoo helper.exe"
  • In HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Active Setup\Installed Components\{1D13U3N1-36Q2-5YON-827Q-6P44RM32N8PS}
    • StubPath = "%Windows%\Yahoo..!\yahoo helper.exe restart"
  • In HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Run
    • YahOO = "%Windows%\Yahoo..!\yahoo helper.exe"
  • In HKEY_CURRENT_USER\Software\XtremeRAT
    • Mutex = "Ckf1dsk7gs"
  • In HKEY_CURRENT_USER\Software\Ckf1dsk7gs
    • ServerStarted = "21/05/2013 23:03:18"
  • In HKEY_CURRENT_USER\Software\Ckf1dsk7gs
    • ServerName = "%Windows%\Yahoo..!\yahoo helper.exe"
  • In HKEY_CURRENT_USER\Software\Ckf1dsk7gs
    • InstalledServer = "%Windows%\Yahoo..!\yahoo helper.exe"

Step 5

Restore these modified registry values

[ Learn More ]

Important:Editing the Windows Registry incorrectly can lead to irreversible system malfunction. Please do this only if you know how to or you can seek your system administrator's help. You may also check out this Microsoft article first before modifying your computer's registry.

  • In HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\DirectDraw\MostRecentApplication
    • From: Name = "svchost.exe"
      To: Name = ""iexplore.exe""
  • In HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\DirectDraw\MostRecentApplication
    • From: ID = "4117ed6"
      To: ID = ""41107b81""
  • In HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\DirectDraw\MostRecentApplication
    • From: Name = "iexplore.exe"
      To: Name = ""iexplore.exe""
  • In HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\DirectDraw\MostRecentApplication
    • From: ID = "4117b81"
      To: ID = ""41107b81""

Step 6

Search and delete these components

[ Learn More ]
There may be some components that are hidden. Please make sure you check the Search Hidden Files and Folders checkbox in the "More advanced options" option to include all hidden files and folders in the search result.
  • %User Temp%\x.html
  • %User Profile%\Windows\Ckf1dsk7gs.xtr
  • %User Profile%\Windows\Ckf1dsk7gs.cfg

Step 7

Search and delete this folder

[ Learn More ]
Please make sure you check the Search Hidden Files and Folders checkbox in the More advanced options option to include all hidden folders in the search result.
  • %Windows%\Yahoo..!

Step 8

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