Analysis by: Christopher Daniel So
 Modified by: rolandde
ALIASES:

Trojan-Downloader.Win32.Agent.gxut (Kaspersky); TrojanDownloader:Win32/Fidjito.A (Microsoft)

 PLATFORM:

Windows 2000, Windows XP, Windows Server 2003

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

  • Threat Type: Trojan

  • Destructiveness: No

  • Encrypted: Yes

  • In the wild: Yes

  OVERVIEW

This Trojan may be dropped by other malware.

It executes the downloaded files. As a result, malicious routines of the downloaded files are exhibited on the affected system. As of this writing, the said sites are inaccessible.

It does not have any information-stealing capability.

  TECHNICAL DETAILS

File Size: 9,728 bytes
File Type: DLL
Memory Resident: Yes
Initial Samples Received Date: 22 Sep 2011

Arrival Details

This Trojan may be dropped by other malware.

Download Routine

This Trojan accesses the following websites to download files:

  • http://www.{BLOCKED}air.com/w123001.html

It saves the files it downloads using the following names:

  • %User Temp%\~AF004F78.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.)

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

As of this writing, the said sites are inaccessible.

Information Theft

This Trojan does not have any information-stealing capability.

NOTES:

It only exhibits its malicious payload if its dropped component's path and file name is %System%\trkwks.dll.

Upon execution, it replaces the following legitimate Microsoft file with its component file:

  • %System%\trkwks.dll

The said component is also detected as TROJ_PAKES.DLL. It then saves an original copy of the overwritten file as follows:

  • %System%\wtrkwks.dll

This routine serves as the malware autostart technique.

It deletes the following file:

  • %System%\regsvr32.exe

  SOLUTION

Minimum Scan Engine: 9.200
FIRST VSAPI PATTERN FILE: 8.446.08
FIRST VSAPI PATTERN DATE: 22 Sep 2011
VSAPI OPR PATTERN File: 8.447.00
VSAPI OPR PATTERN Date: 23 Sep 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

Scan your computer with your Trend Micro product and note files detected as TROJ_PAKES.DLL

Step 3

Restart in Safe Mode

[ Learn More ]

Step 4

Search and delete the file detected as TROJ_PAKES.DLL

[ 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 5

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.
  • %User Temp%\~AF004F78.tmp

Step 6

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

Step 7

Restore these deleted files from backup

*Note: Only Microsoft-related keys/values will be restored. If this malware/grayware also deleted registry keys/values related to programs that are not from Microsoft, please reinstall those programs on your computer.

%System%\regsvr32.exe
  • %System%\trkwks.dll

    • NOTES:

    If the malware was detected at%System%\trkwks.dll, perform the following:

    1. Insert your Windows Installation CD in your CD-ROM then restart your computer.
    2. When prompted on the Main Menu, type r to enter the Recovery Console.
      (Note: On Windows 2000, after pressing r, type c to choose the Recovery Console in the repair options screen.)
    3. When prompted, type your administrator password to log on.
    4. Type the following set of commands, then press Enter for each:
      {Drive letter of your CD-ROM where the Windows Installation CD is inserted}{colon}
      e.g. D: or E:
      cd i386
      expand.exe trkwks.dl_ %System%


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