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TROJ_DROPPER.MRX

February 07, 2013
 Analysis by: Rhena Inocencio
 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:
 SYSTEM IMPACT RATING:
 INFORMATION EXPOSURE:

  • 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:

245,248 bytes

File Type:

EXE

Memory Resident:

Yes

Initial Samples Received Date:

05 Feb 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 and executes the following files:

  • %User Temp%\{random}.tmp\msupdate.exe
  • %User Temp%\{random}.tmp\PsExec.bat
  • %User Temp%\{random}.tmp\PsExec.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, or C:\Users\{user name}\AppData\Local\Temp on Windows Vista and 7.)

It creates the following folders:

  • %User Temp%\{random}.tmp

(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.)

Other System Modifications

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

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\
services\SharedAccess\Parameters\
FirewallPolicy\FirewallRules
{GUID} = "v2.10|Action=Allow|Active=TRUE|Dir=In|Protocol=17|Profile=Public|App=%User Temp%\{random}.tmp\PsExec.exe|Name=enable|"

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\
services\SharedAccess\Parameters\
FirewallPolicy\FirewallRules
{GUID} = "v2.10|Action=Allow|Active=TRUE|Dir=In|Protocol=6|Profile=Public|App=%User Temp%\{random}.tmp\msupdate.exe|Name=enable|"

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\
services\SharedAccess\Parameters\
FirewallPolicy\FirewallRules
{GUID} = "v2.10|Action=Allow|Active=TRUE|Dir=In|Protocol=17|Profile=Public|App=%User Temp%\{random}.tmp\msupdate.exe|Name=enable|"

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\
services\SharedAccess\Parameters\
FirewallPolicy\FirewallRules
{GUID} = "v2.10|Action=Allow|Active=TRUE|Dir=In|App=%Application Data%\{random folder name 1}\{random file name 1}.exe|Name=explore|"

NOTES:

The dropped files are deleted after successful execution.

  SOLUTION

Minimum Scan Engine:

9.300

FIRST VSAPI PATTERN FILE:

9.708.04

FIRST VSAPI PATTERN DATE:

05 Feb 2013

VSAPI OPR PATTERN File:

9.709.00

VSAPI OPR PATTERN Date:

06 Feb 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

Scan your computer with your Trend Micro product and note files detected as TROJ_DROPPER.MRX

Step 3

Restart in Safe Mode

[ Learn More ]

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\FirewallRules
    • {GUID} = "v2.10|Action=Allow|Active=TRUE|Dir=In|Protocol=6|Profile=Public|App=%User Temp%\{random}.tmp\PsExec.exe|Name=enable|"
  • In HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\services\SharedAccess\Parameters\FirewallPolicy\FirewallRules
    • {GUID} = "v2.10|Action=Allow|Active=TRUE|Dir=In|Protocol=17|Profile=Public|App=%User Temp%\{random}.tmp\PsExec.exe|Name=enable|"
  • In HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\services\SharedAccess\Parameters\FirewallPolicy\FirewallRules
    • {GUID} = "v2.10|Action=Allow|Active=TRUE|Dir=In|Protocol=6|Profile=Public|App=%User Temp%\{random}.tmp\msupdate.exe|Name=enable|"
  • In HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\services\SharedAccess\Parameters\FirewallPolicy\FirewallRules
    • {GUID} = "v2.10|Action=Allow|Active=TRUE|Dir=In|Protocol=17|Profile=Public|App=%User Temp%\{random}.tmp\msupdate.exe|Name=enable|"

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.  
  • %User Temp%\{random}.tmp

Step 6

Search and delete the file detected as TROJ_DROPPER.MRX

[ Learn More ]
Please make sure you check the Search Hidden Files and Folders checkbox in the More advanced options option to include all hidden files in the search result.

Step 7

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