Analysis by: Sammy Chua
ALIASES:

TrojanDownloader:Win32/Dalexis (Microsoft), Trojan-Downloader.Win32.Cabby.cbtu (Kaspersky), Win32/TrojanDownloader.Elenoocka.A (ESET), TR/Cabhot.A.109 (Avira), Downloader.Agent.16.AA (AVG), Trojan.Agent.BHHW (BitDefender)

 PLATFORM:

Windows

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

It modifies the Internet Explorer Zone Settings.

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

  TECHNICAL DETAILS

File Size: 31,232 bytes
File Type: EXE
Memory Resident: No
Initial Samples Received Date: 24 Jan 2015

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 the following file(s)/component(s):

  • %User Temp%\{original file name}.rtf
  • %User Temp%\temp_cab_{random number}.cab

(Note: %User Temp% is the user's temporary folder, where it usually is C:\Documents and Settings\{user name}\Local Settings\Temp on Windows 2000, Windows Server 2003, and Windows XP (32- and 64-bit); C:\Users\{user name}\AppData\Local\Temp on Windows Vista (32- and 64-bit), Windows 7 (32- and 64-bit), Windows 8 (32- and 64-bit), Windows 8.1 (32- and 64-bit), Windows Server 2008, and Windows Server 2012.)

It adds the following mutexes to ensure that only one of its copies runs at any one time:

  • 56730099

Web Browser Home Page and Search Page Modification

This Trojan modifies the Internet Explorer Zone Settings.

Download Routine

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

  • {BLOCKED}-photographe.com/tmp/pack.tar.gz
  • {BLOCKED}gt-its.de/fit/pack.tar.gz
  • {BLOCKED}dessources.com/assets/pack.tar.gz
  • {BLOCKED}system.fr/jb/pack.tar.gz
  • {BLOCKED}de.asso.fr/piwigotest/pack.tar.gz
  • {BLOCKED}lapedia.org/histoiredesarts/pack.tar.gz

It saves the files it downloads using the following names:

  • %User Temp%\{random number}.exe - decrypted from download URL, detected as TROJ_CRYPCTB.YN

(Note: %User Temp% is the user's temporary folder, where it usually is C:\Documents and Settings\{user name}\Local Settings\Temp on Windows 2000, Windows Server 2003, and Windows XP (32- and 64-bit); C:\Users\{user name}\AppData\Local\Temp on Windows Vista (32- and 64-bit), Windows 7 (32- and 64-bit), Windows 8 (32- and 64-bit), Windows 8.1 (32- and 64-bit), Windows Server 2008, and Windows Server 2012.)

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

Other Details

This Trojan connects to the following URL(s) to check for an Internet connection:

  • windowsupdate.microsoft.com

It opens the following files:

  • %User Temp%\{original file name}.rtf

(Note: %User Temp% is the user's temporary folder, where it usually is C:\Documents and Settings\{user name}\Local Settings\Temp on Windows 2000, Windows Server 2003, and Windows XP (32- and 64-bit); C:\Users\{user name}\AppData\Local\Temp on Windows Vista (32- and 64-bit), Windows 7 (32- and 64-bit), Windows 8 (32- and 64-bit), Windows 8.1 (32- and 64-bit), Windows Server 2008, and Windows Server 2012.)

NOTES:

It tries to download the encrypted file from the URLs, checks the downloaded data, decrypts and verifies if it matches the file it wants to download. If not, it will continue to try to download the correct file from the list of URLs.

  SOLUTION

Minimum Scan Engine: 9.700
FIRST VSAPI PATTERN FILE: 11.424.05
FIRST VSAPI PATTERN DATE: 20 Jan 2015
VSAPI OPR PATTERN File: 11.425.00
VSAPI OPR PATTERN Date: 21 Jan 2015

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

Note that not all files, folders, and registry keys and entries are installed on your computer during this malware's/spyware's/grayware's execution. This may be due to incomplete installation or other operating system conditions. If you do not find the same files/folders/registry information, please proceed to the next step.

Step 3

Scan your computer with your Trend Micro product and note files detected as TROJ_DALEXIS.G

Step 4

Restart in Safe Mode

[ Learn More ]

Step 5

Search and delete the files detected as TROJ_DALEXIS.G

*Note: Some component files may be 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.

To stop the malware/grayware from running when certain files are opened:

For Windows 2000, Windows XP, and Windows Server 2003:

  1. Right-click Start then click Search....
  2. In the File name* input box, type the name of the file that was detected earlier.
  3. In the Look In drop-down list, select My Computer then press Enter.
  4. Once located, select the file then press SHIFT+DELETE to delete it.
    *Note: The file name input box title varies depending on the Windows version (e.g. Search for files or folders named or All or part of the file name.).

For Windows Vista, Windows 7, Windows Server 2008, Windows 8, Windows 8.1, and Windows Server 2012 (R2):

  1. Open a Windows Explorer window.
    • For Windows Vista, 7, and Server 2008 users, click Start>Computer.
    • For Windows 8, 8.1, and Server 2012 users, right-click on the lower left corner of the screen,then click File Explorer.
  2. In the Search Computer/This PC input box, type the name of the file that was detected earlier.
  3. Once located, select the file then press SHIFT+DELETE to delete it.
    *Note: Read the following Microsoft page if these steps do not work on Windows 7.

Step 6

Search and delete these files

[ Learn More ]
There may be some 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%\temp_cab_{random number}.cab
  • %User Temp%\{original file name}.rtf

Step 7

Remove malware/grayware files dropped/downloaded by TROJ_DALEXIS.G. (Note: Please skip this step if the threats listed below have already been removed.)

    • TROJ_CRYPCTB.YN

Step 8

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