TROJ_OFICLA.CYW

 Analysis by: Christopher Daniel So

 ALIASES:

Trojan:Win32/Oficla (Microsoft); Trojan.Zbot (Symantec); Trojan-Banker.Win32.Banker.bgsd (Kaspersky); Trojan.Win32.Oficla (Ikarus)

 PLATFORM:

Windows 2000, Windows XP, Windows Server 2003

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

  • Threat Type: Trojan

  • Destructiveness: No

  • Encrypted: Yes

  • In the wild: Yes

  OVERVIEW

This Trojan arrives as attachment to mass-mailed email messages.

It connects to certain URLs. It may do this to remotely inform a malicious user of its installation. It may also do this to download possibly malicious files onto the computer, which puts the computer at a greater risk of infection by other threats. It executes the downloaded files. As a result, malicious routines of the downloaded files are exhibited on the affected system.

  TECHNICAL DETAILS

File Size:

43,520 bytes

File Type:

PE

File Compression:

UPX

Memory Resident:

Yes

Initial Samples Received Date:

22 Feb 2011

Payload:

Downloads files

Arrival Details

This Trojan arrives as attachment to mass-mailed email messages.

Installation

This Trojan drops the following copies of itself into the affected system:

  • %User Profile%\Application Data\{random folder name}\csrss.exe

(Note: %User Profile% is the current user's profile folder, which is usually C:\Windows\Profiles\{user name} on Windows 98 and ME, C:\WINNT\Profiles\{user name} on Windows NT, and C:\Documents and Settings\{user name} on Windows 2000, XP, and Server 2003.)

It creates the following folders:

  • %User Profile%\Application Data\{random folder name}

(Note: %User Profile% is the current user's profile folder, which is usually C:\Windows\Profiles\{user name} on Windows 98 and ME, C:\WINNT\Profiles\{user name} on Windows NT, and C:\Documents and Settings\{user name} on Windows 2000, XP, and Server 2003.)

Autostart Technique

This Trojan modifies the following registry entries to ensure it automatic execution at every system startup:

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\
Windows NT\CurrentVersion\Winlogon
Shell = "explorer.exe "%User Profile%\Application Data\{random folder name}\csrss.exe""

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

Other System Modifications

This Trojan adds the following registry entries:

HKEY_CURRENT_USER\Software\Microsoft
setiasworld = "{random characters}"

It creates the following registry entry(ies) to bypass Windows Firewall:

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\
Services\SharedAccess\Parameters\
FirewallPolicy\StandardProfile\AuthorizedApplications\
List
{malware path and file name} = "{malware path and file name}:*:Enabled:ldrsoft"

Download Routine

This Trojan connects to the following malicious URLs:

  • http://{BLOCKED}us.ru/cnn/img.php?v=1&id={random characters}&b=&tm=1&os=&av=&br=&

It accesses the following websites to download files:

  • http://www.{BLOCKED}ta.net/geza/pot.exe
  • http://www.{BLOCKED}tta.net/css/spm3.exe

It saves the files it downloads using the following names:

  • %User Temp%\{random number}.exe

(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.)

Trend Micro detects the dowloaded file as:

  • TROJ_ZBOT.SMHA

It then executes the downloaded files. As a result, malicious routines of the downloaded files are exhibited on the affected system.

  SOLUTION

Minimum Scan Engine:

8.900

FIRST VSAPI PATTERN FILE:

7.856.11

FIRST VSAPI PATTERN DATE:

25 Feb 2011

VSAPI OPR PATTERN File:

7.857.00

VSAPI OPR PATTERN Date:

25 Feb 2011

Step 1

For Windows XP and Windows Server 2003 users, before doing any scans, please make sure you disable System Restore to allow full scanning of your computer.

Step 2

Remove malware files dropped/downloaded by TROJ_OFICLA.CYW

    • TROJ_ZBOT.SMHA

Step 3

Identify and terminate files detected as TROJ_OFICLA.CYW

[ Learn More ]
  1. If the detected file is displayed in either Windows Task Manager or Process Explorer but you cannot delete it, restart your computer in safe mode. To do this, refer to this link for the complete steps.
  2. If the detected file is not displayed in either Windows Task Manager or Process Explorer, continue doing the next steps.

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\SYSTEM\CurrentControlSet\Services\SharedAccess\Parameters\FirewallPolicy\StandardProfile\AuthorizedApplications\List
    • {malware path and file name} = "{malware path and file name}:*:Enabled:ldrsoft"
  • In HKEY_CURRENT_USER\Software\Microsoft
    • setiasworld = "{random characters}"

Step 5

Restore this modified 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 NT\CurrentVersion\Winlogon
    • From: Shell = "explorer.exe "%User Profile%\Application Data\{random folder name}\csrss.exe""
      To: Shell = "Explorer.exe"

Step 6

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.
  • %User Profile%\Application Data\{random folder name}

Step 7

Scan your computer with your Trend Micro product to delete files detected as TROJ_OFICLA.CYW. 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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