Analysis by: Christopher Daniel So
ALIASES:

Exploit-MSExcel.u !! (McAfee)

 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 as attachment to mass-mailed email messages.

  TECHNICAL DETAILS

File Size: 75,287 bytes
File Type: XLS
Memory Resident: No
Initial Samples Received Date: 22 Mar 2011

Arrival Details

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

Installation

This Trojan drops the following files:

  • %User Temp%\taskmgr.exe
  • %User Temp%\{malware file name}.xls

(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.)

Autostart Technique

This Trojan registers its dropped component as a system service to ensure its automatic execution at every system startup. It does this by creating the following registry entries:

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\
Services\6to4
Type = 20

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\
Services\6to4
Start = 2

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\
Services\6to4
ErrorControl = 1

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\
Services\6to4
ImagePath = "%SystemRoot%\System32\svchost.exe -k netsvcs"

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\
Services\6to4
DisplayName = "Network Provider Service "

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\
Services\6to4
Description = "Service that offers Security network whith Outlook Express. It shuodn't be stopped unless Special service needed or you known how to contrl."

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\
Services\6to4\Parameters
ServiceDll = "%System%\dmdskngr.dll"

It registers its dropped component as a system service to ensure its automatic execution at every system startup. It does this by creating the following registry keys:

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\
Services\6to4

Dropping Routine

This Trojan drops the following files:

  • %System%\dmdskngr.dll - detected as BKDR_SMALL.KCA

(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: 8.900
FIRST VSAPI PATTERN FILE: 7.918.09
FIRST VSAPI PATTERN DATE: 22 Mar 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_MDROP.KZ

    BKDR_SMALL.KCA

Step 3

Restart in Safe Mode

[ Learn More ]

Step 4

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\SYSTEM\CurrentControlSet\Services
    • 6to4

Step 5

Search and delete these files

[ Learn More ]
There may be some component files 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%\taskmgr.exe
  • %User Temp%\{malware file name}.xls

Step 6

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