Analysis by: Jaime Benigno Reyes
ALIASES:

TrojanDownloader:Win32/Small.gen!AP (Microsoft), Mal/DownLdr-AC (Sophos), Downloader.Rozena (AVG)

 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: Trojan

  • Destructiveness: No

  • Encrypted: Yes

  • 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.

It executes the downloaded files. As a result, malicious routines of the downloaded files are exhibited on the affected system.

  TECHNICAL DETAILS

File Size: Varies
File Type: EXE
Memory Resident: No
Initial Samples Received Date: 21 Mar 2013
Payload: Downloads 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.

Download Routine

This Trojan connects to the following URL(s) to download its component file(s):

  • http://www.{BLOCKED}a.com/rgboard/data/skins/xupdate.exe - also detected as TROJ_DLOAD.KRS
  • http://www.{BLOCKED}a.com/rgboard/data/skins/paper.gif - detected as TSPY_INJECTO.KRS

It saves the files it downloads using the following names:

  • %User Temp%\v3servc.exe - TROJ_DLOAD.KRS
  • %User Temp%\ahnsvc1.exe - TSPY_INJECTO.KRS

(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 then executes the downloaded files. As a result, malicious routines of the downloaded files are exhibited on the affected system.

  SOLUTION

Minimum Scan Engine: 9.300
FIRST VSAPI PATTERN FILE: 9.806.01
FIRST VSAPI PATTERN DATE: 21 Mar 2013
VSAPI OPR PATTERN File: 9.807.00
VSAPI OPR PATTERN Date: 21 Mar 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

Remove malware/grayware files dropped/downloaded by TROJ_DLOAD.KRS

     
    • TSPY_INJECTO.KRS

Step 3

Scan your computer with your Trend Micro product to delete files detected as TROJ_DLOAD.KRS. 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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