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BKDR_DORIFEL.AE

April 09, 2013
 Analysis by: Anthony Joe Melgarejo
 ALIASES:

VirTool:Win32/Obfuscator.ADH (Microsoft), PWS-Zbot-FASW!8C9349562076 (McAfee), W32/Dorifel.ACTZ!tr (Fortinet), Trojan.Win32.Bublik (Ikarus), Win32/Kryptik.AXXZ trojan (ESET)

 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: Backdoor

  • Destructiveness: No

  • Encrypted: Yes

  • In the wild: Yes

  OVERVIEW

Infection Channel:

Downloaded from the Internet, Dropped by other malware

This backdoor 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 then deletes itself afterward.

  TECHNICAL DETAILS

File Size:

50,176 bytes

File Type:

EXE

Memory Resident:

Yes

Initial Samples Received Date:

03 Apr 2013

Payload:

Downloads files, Compromises system security

Arrival Details

This backdoor 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 backdoor executes then deletes itself afterward.

It injects threads into the following normal process(es):

  • svchost.exe

Autostart Technique

This backdoor adds the following registry entries to enable its automatic execution at every system startup:

HKEY_CURRENT_USER\Software\Microsoft\
Windows\CurrentVersion\Run
MSConfig = ""%User Profile%\{Random File Name}.exe""

Backdoor Routine

This backdoor connects to the following URL(s) to send and receive commands from a remote malicious user:

  • http://{BLOCKED}.{BLOCKED}.99.250.178/daol/asidfk11.dat?wv=51&bt=32

NOTES:
It downloads a JPG file from the following link:

  • http://{BLOCKED}report.com/images/2009/05/naughty-elephant.jpg

It then saves and open it as follows:

  • %Current Folder%\{Malware Name}.jpg

This is done to trick users into thinking that the executed file is legitimate.

It then connects to the following URL to download a file MeNakedTIFF.exe:

  • http://{BLOCKED}.{BLOCKED}.99.250.178/daol/oadl.php

It saves a copy of the downloaded file as %User Profile%\{Random File Name}.exe and execute it. Trend Micro also detects the downloaded file as BKDR_DORIFEL.AE.

This backdoor may compose messages that can be part of its spamming routine. It uses any of the following Simple Mail Transfer Protocol (SMTP) servers to send its messages:

  • 207.46.100.11
  • 66.196.118.35
  • aspmx.l.google.com
  • mxs.mail.ru
  • alt1.aspmx.l.google.com
  • alt2.aspmx.l.google.com

  SOLUTION

Minimum Scan Engine:

9.300

FIRST VSAPI PATTERN FILE:

9.834.02

FIRST VSAPI PATTERN DATE:

03 Apr 2013

VSAPI OPR PATTERN File:

9.835.00

VSAPI OPR PATTERN Date:

04 Apr 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 BKDR_DORIFEL.AE

Step 3

Restart in Safe Mode

[ Learn More ]

Step 4

Delete this registry value

[ Learn More ]

Important: Editing the Windows Registry incorrectly can lead to irreversible system malfunction. Please do this step only if you know how or you can ask assistance from your system administrator. Else, check this Microsoft article first before modifying your computer's registry.

  • In HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Run
    • MSConfig = ""%User Profile%\{Random File Name}.exe""

Step 5

Search and delete this file

[ 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.
  • %Current Folder%\{Malware Name}.jpg

Step 6

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