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Threat Encyclopedia

TROJ_DIDKR.A

ANALYSIS BY

Alvin Bacani


ALIASES:

Trojan/Win32.Ddkr (AhnLab)

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:
INFORMATION EXPOSURE:

  • Threat Type:Trojan

  • Destructiveness:No

  • Encrypted: Yes

  • In the wild: Yes

OVERVIEW

Infection Channel:

Downloaded from the Internet


This malware is related to the security incident that affected certain government and news websites in South Korea. Cybercriminals compromised the auto-update mechanism of a file-sharing software in order to serve a modified malicious version of the said software's installer.

To get a one-glance comprehensive view of the behavior of this Trojan, refer to the Threat Diagram shown below.

This is the detection for the modified version of the SimDisk file-sharing software. It is downloaded as an 'update' on affected systems.

When executed on a system, it downloads other components. The downloaded components include a Tor client, a configuration file, and a file that connects to the Tor network. This malware's use of Tor hides its activities from affected users.

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:

18,785,561 bytes

File Type:

EXE

Memory Resident:

Yes

Initial Samples Received Date:

25 Jun 2013

Payload:

Downloads files, Drops files

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%\RarSFX0\SimDisk.exe
  • %User Temp%\RarSFX0\SimDiskup.exe - detected as TROJ_DIDKR.A

(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.)

Download Routine

This Trojan connects to the following website(s) to download and execute a malicious file:

  • http://www.{BLOCKED}g.co.kr/images/korea/c.jpg - detected as TROJ_DIDKR.A

NOTES:

The dropped malware file SimDiskUp.exe accesses the aforementioned URL to download another malware. Once executed, the downloaded file creates the following folders:

  • %Application Data%\tor
  • %Application Data%\Identities\{GUID}

It drops and executes the following files:

  • %Application Data%\Identities\{GUID}\{Random File Name 1} - TROJ_DIDKR.A
  • %Application Data%\Identities\{GUID}\{Random File Name 2} - Tor Client

It uses a file name similar to a legitimate file to pass as a legitimate file. It then drops the component %Application Data%\Identities\{GUID}\config.ini. The said file contains file name of the Tor client, affected machine's IP address, and country.

SOLUTION

Minimum Scan Engine:

9.300

VSAPI OPR PATTERN File:

10.117.00

VSAPI OPR PATTERN Date:

26 Jun 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_DIDKR.A

Step 3

Search and delete these folders

[ 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%\RarSFX0
  • %Application Data%\tor
  • %Application Data%\Identities\{GUID}

Step 4

Scan your computer with your Trend Micro product to delete files detected as TROJ_DIDKR.A. 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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