TROJ_DROPPER.CN

October 09, 2012
 Analysis by: Sabrina Lei Sioting
 Modified by: Michael Cabel
 PLATFORM:

Windows 2000, Windows XP, Windows Server 2003

 OVERALL RISK RATING:
 DAMAGE POTENTIAL:
 DISTRIBUTION POTENTIAL:
 REPORTED INFECTION:

  • Threat Type: Trojan

  • Destructiveness: No

  • Encrypted: No

  • 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 dropped file(s). As a result, malicious routines of the dropped files are exhibited on the affected system.

  TECHNICAL DETAILS

File Size:

Varies

File Type:

EXE

Memory Resident:

No

Initial Samples Received Date:

04 Jul 2011

Payload:

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 creates the following folders:

  • %System Root%\WINNT\system32\dllcache

(Note: %System Root% is the root folder, which is usually C:\. It is also where the operating system is located.)

Dropping Routine

This Trojan drops the following files:

  • %System Root%\WINNT\system32\drivers\etc\DISKINFO.EXE - detected as HKTL_DISKINFO
  • %System Root%\WINNT\system32\dllcache\hidden32.exe - detected as HKTL_HIDEWIN.A
  • %System Root%\WINNT\system32\dllcache\runbatch.exe- detected as BKDR_SERVU.J
  • %System Root%\WINNT\system32\dllcache\psexec.bat - detected as BAT_IPC.A
  • %System Root%\WINNT\system32\dllcache\userlist.exe - detected as BKDR_IROFFER.S
  • %System Root%\WINNT\system32\drivers\etc\Drives.txt
  • %System Root%\WINNT\system32\drivers\etc\Rar.exe
  • %System Root%\WINNT\system32\drivers\etc\tar.exe
  • %System Root%\WINNT\system32\drivers\etc\test.rar
  • %System Root%\WINNT\system32\dllcache\cygcrypt-0.dll
  • %System Root%\WINNT\system32\dllcache\cygwin1.dll
  • %System Root%\WINNT\system32\dllcache\del.bat
  • %System Root%\WINNT\system32\dllcache\FireDaemon.exe
  • %System Root%\WINNT\system32\dllcache\mss.ini
  • %System Root%\WINNT\system32\dllcache\regkeyadd.reg
  • %System Root%\WINNT\system32\dllcache\ServrStartUpLog.txt
  • %System Root%\WINNT\system32\dllcache\ServUDaemon.ini
  • %System Root%\WINNT\system32\dllcache\tar.exe
  • %System Root%\WINNT\system32\dllcache\TzoLibr.dll
  • %System Root%\WINNT\system32\dllcache\welcome.txt
  • %System Root%\WINNT\system32\dllcache\wincfg.com
  • %System Root%\WINNT\system32\dllcache\winignore.ign
  • %System Root%\WINNT\system32\dllcache\winmsg.msg
  • %System Root%\WINNT\system32\dllcache\winnotify.net
  • %System Root%\WINNT\system32\dllcache\winstartup.log
  • %System Root%\WINNT\system32\dllcache\x.bat
  • %System Root%\WINNT\system32\dllcache\xdcc.config

It sets the attributes of its dropped file(s) to the following:

  • System
  • Hidden

It executes the dropped file(s). As a result, malicious routines of the dropped files are exhibited on the affected system.

  SOLUTION

Minimum Scan Engine:

8.900

FIRST VSAPI PATTERN FILE:

8.266.03

FIRST VSAPI PATTERN DATE:

04 Jul 2011

VSAPI OPR PATTERN File:

8.267.00

VSAPI OPR PATTERN Date:

04 Jul 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_DROPPER.CN

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.
  • %System Root%\WINNT\system32\dllcache

Step 4

Search and delete this file

[ 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.
  • %System Root%\WINNT\system32\drivers\etc\Drives.txt
  • %System Root%\WINNT\system32\dllcache\hidden32.exe
  • %System Root%\WINNT\system32\dllcache\psexec.bat
  • %System Root%\WINNT\system32\drivers\etc\Rar.exe
  • %System Root%\WINNT\system32\drivers\etc\tar.exe
  • %System Root%\WINNT\system32\drivers\etc\test.rar

Step 5

Scan your computer with your Trend Micro product to delete files detected as TROJ_DROPPER.CN. 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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