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TROJ_SASFIS.BT

 Analysis by: Christopher Daniel So

 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:

23,040 bytes

File Type:

EXE

Memory Resident:

Yes

Initial Samples Received Date:

03 Oct 2009

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.

Other System Modifications

This Trojan adds the following registry entries:

HKEY_CURRENT_USER\Software\Microsoft\
Office\11.0\Word\
Security
AccessVBOM = "0"

HKEY_CURRENT_USER\Software\Microsoft\
Office\11.0\Word\
Security
Level = "4"

It modifies the following registry entries:

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\
Windows NT\CurrentVersion\Winlogon
Shell = "Explorer.exe rundll32.exe prqy.fko jfvgah"

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

Dropping Routine

This Trojan drops the following files:

  • %System%\prqy.fko

(Note: %System% is the Windows system folder, which is usually C:\Windows\System on Windows 98 and ME, C:\WINNT\System32 on Windows NT and 2000, or C:\Windows\System32 on Windows XP and Server 2003.)

  SOLUTION

Minimum Scan Engine:

9.200

FIRST VSAPI PATTERN FILE:

6.506.01

FIRST VSAPI PATTERN DATE:

05 Oct 2009

VSAPI OPR PATTERN File:

6.507.00

VSAPI OPR PATTERN Date:

05 Oct 2009

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

Since this malware uses rootkit technology, detection and removal using normal and safe mode methods may not eliminate it completely. This procedure restarts the system using the Windows Recovery Console.

  1. Insert the Windows Installation CD into the CD drive, then Press the restart button.
  2. Upon prompt, press any key to boot from the CD.
  3. On the main menu, type r to go to the Recovery Console.
  4. Type the drive that contains Windows (usually C:) and press Enter.
  5. In the input box, type the following then press Enter:
     del %System%\prqy.fko
  6. Type exit and press Enter to restart the system normally.

Step 3

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_CURRENT_USER\Software\Microsoft\Office\11.0\Word\Security
    • AccessVBOM = "0"
  • In HKEY_CURRENT_USER\Software\Microsoft\Office\11.0\Word\Security
    • Level = "4"

Step 4

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 rundll32.exe prqy.fko jfvgah"
      To: Shell = "Explorer.exe"

Step 5

Scan your computer with your Trend Micro product to delete files detected as TROJ_SASFIS.BT. 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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