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WORM_SLENFBOT.LK

April 15, 2013
 Analysis by: Mark Joseph Manahan
 ALIASES:

Worm:Win32/Slenfbot (Microsoft), Trojan.Win32.Jorik.IRCbot.ghc (Kaspersky), W32.IRCBot (Symantec)

 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:

  • Threat Type: Worm

  • Destructiveness: No

  • Encrypted:

  • In the wild: Yes

  OVERVIEW


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

It drops an AUTORUN.INF file to automatically execute the copies it drops when a user accesses the drives of an affected system.

  TECHNICAL DETAILS

File Size:

168,960 bytes

File Type:

EXE

Memory Resident:

Yes

Initial Samples Received Date:

08 Apr 2013

Arrival Details

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

  • %System%\igfxvk32.exe

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

Autostart Technique

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

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\
Windows\CurrentVersion\Run
Intel Virtual Config = "%System%\igfxvk32.exe"

Other System Modifications

This worm adds the following registry keys:

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\
Windows NT\CurrentVersion\AppCompatFlags\
Layers

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\
Windows NT\CurrentVersion\AppCompatFlags

It adds the following registry entries:

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\
Windows NT\CurrentVersion\AppCompatFlags\
Layers
%System%\igfxvk32.exe = "DisableNXShowUI"

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\
Services\SharedAccess\Parameters\
FirewallPolicy\DomainProfile\AuthorizedApplications\
List
%System%\igfxvk32.exe = "%System%\igfxvk32.exe:*:Enabled:Intel Virtual Config"

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\
Services\SharedAccess\Parameters\
FirewallPolicy\StandardProfile\AuthorizedApplications\
List
%System%\igfxvk32.exe = "%System%\igfxvk32.exe:*:Enabled:Intel Virtual Config"

Propagation

This worm creates the following folders in all removable drives:

  • DataMgr.{645FF040-5081-101B-9F08-00AA002F954E}

It drops the following copy(ies) of itself in all removable drives:

  • DataMgr.{645FF040-5081-101B-9F08-00AA002F954E}\datamgr-x4297028.c32

It drops an AUTORUN.INF file to automatically execute the copies it drops when a user accesses the drives of an affected system.

The said .INF file contains the following strings:

[Autorun]
open=CMD /C START DataMgr.{645FF040-5081-101B-9F08-00AA002F954E}\datamgr-x4297028.c32
icon=%windir%\system32\SHELL32.dll,3
action=Browse the contents of the drive.
shell\open=Open
shell\open\command=CMD /C START DataMgr.{645FF040-5081-101B-9F08-00AA002F954E}\datamgr-x4297028.c32
shell\open\default=1
shell\explore=Explore
shell\explore\command=CMD /C START DataMgr.{645FF040-5081-101B-9F08-00AA002F954E}\datamgr-x4297028.c32
shell\search=Search...
shell\search\command=CMD /C START DataMgr.{645FF040-5081-101B-9F08-00AA002F954E}\datamgr-x4297028.c32
useautoplay=1

Other Details

This worm connects to the following possibly malicious URL:

  • s13.{BLOCKED}ids.su
  • s51.{BLOCKED}ids.su
  • s27.{BLOCKED}ids.su

  SOLUTION

Minimum Scan Engine:

9.300

FIRST VSAPI PATTERN FILE:

9.844.05

FIRST VSAPI PATTERN DATE:

08 Apr 2013

VSAPI OPR PATTERN File:

9.845.00

VSAPI OPR PATTERN Date:

09 Apr 2013

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_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows NT\CurrentVersion
    • AppCompatFlags

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
    • Intel Virtual Config = "%System%\igfxvk32.exe"
  • In HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\SharedAccess\Parameters\FirewallPolicy\DomainProfile\AuthorizedApplications\List
    • %System%\igfxvk32.exe = "%System%\igfxvk32.exe:*:Enabled:Intel Virtual Config"
  • In HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\SharedAccess\Parameters\FirewallPolicy\StandardProfile\AuthorizedApplications\List
    • %System%\igfxvk32.exe = "%System%\igfxvk32.exe:*:Enabled:Intel Virtual Config"

Step 5

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.
  • DataMgr.{645FF040-5081-101B-9F08-00AA002F954E}

Step 6

Search and delete AUTORUN.INF files created by WORM_SLENFBOT.LK that contain these strings

[ Learn More ]
[Autorun]
open=CMD /C START DataMgr.{645FF040-5081-101B-9F08-00AA002F954E}\datamgr-x4297028.c32
icon=%windir%\system32\SHELL32.dll,3
action=Browse the contents of the drive.
shell\open=Open
shell\open\command=CMD /C START DataMgr.{645FF040-5081-101B-9F08-00AA002F954E}\datamgr-x4297028.c32
shell\open\default=1
shell\explore=Explore
shell\explore\command=CMD /C START DataMgr.{645FF040-5081-101B-9F08-00AA002F954E}\datamgr-x4297028.c32
shell\search=Search...
shell\search\command=CMD /C START

Step 7

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