BKDR_ASNET.YVAGE

September 08, 2014
 Analysis by: Rika Joi Gregorio
 ALIASES:

Trojan:Win32/Neop!gmb(Microsoft), RDN/Generic Downloader.x!km(McAfee), W32/Vobfus.NQO!tr(Fortinet), Trojan.Win32.Vobfus(Ikarus), Win32/Autoit.NQO 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:
 INFORMATION EXPOSURE:

  • Threat Type: Backdoor

  • Destructiveness: No

  • Encrypted: Yes

  • In the wild: Yes

  OVERVIEW

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 commands from a remote malicious user, effectively compromising the affected system.

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

It adds accounts to have an administrator privilege. This allows the malware or a malicious user to perform tasks that may put the affected system in greater risk.

  TECHNICAL DETAILS

File Size:

411,136 bytes

File Type:

EXE

Memory Resident:

Yes

Initial Samples Received Date:

16 Jul 2014

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 drops the following non-malicious file:

  • %System%\sethc.exe - copy of cmd.exe

(Note: %System% is the Windows system folder, which is usually C:\Windows\System32.)

Other System Modifications

This backdoor adds the following registry entries:

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\
Windows NT\CurrentVersion\Winlogon\
SpecialAccounts\UserList
AstNet = "0"

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\
Windows NT\CurrentVersion\Winlogon\
SpecialAccounts\UserList
server_sys = "0"

Backdoor Routine

This backdoor executes the following commands from a remote malicious user:

  • Perform remote shell

Download Routine

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

  • http://www.{BLOCKED}ron.com.tw/images/logo3.png

It connects to the following URL(s) to download its configuration file:

  • www.{BLOCKED}ayu.com.my/images/history3.jpg

It saves the files it downloads using the following names:

  • %User Temp%\germans.ini - config file
  • %User Temp%\hmmo32.exe - detected as TSPY_ZBOT.YYDAP

(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.

Information Theft

This backdoor s configuration file contains the following information:

  • Download link of malicious file

Other Details

This backdoor adds the following accounts to the Administrator group:

  • server_sys
  • AstNet

  SOLUTION

Minimum Scan Engine:

9.700

FIRST VSAPI PATTERN FILE:

11.132.04

FIRST VSAPI PATTERN DATE:

06 Sep 2014

VSAPI OPR PATTERN File:

11.133.00

VSAPI OPR PATTERN Date:

07 Sep 2014

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

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

     
    • TSPY_ZBOT.YYDAP

Step 4

Scan your computer with your Trend Micro product and note files detected as BKDR_ASNET.YVAGE

Step 5

Terminate the malware/grayware/spyware process:

[ Learn More ]
  1. If the detected file is displayed in either Windows Task Manager or Process Explorer but you cannot delete it, restart your computer in safe mode. To do this, refer to this link for the complete steps.
  2. If the detected file is not displayed in either Windows Task Manager or Process Explorer, continue doing the next steps.

Step 6

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_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows NT\CurrentVersion\Winlogon\SpecialAccounts\UserList
    • AstNet = "0"
  • In HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows NT\CurrentVersion\Winlogon\SpecialAccounts\UserList
    • server_sys = "0"

Step 7

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.
  • %System%\sethc.exe
  • %User Temp%\germans.ini

Step 8

Scan your computer with your Trend Micro product to delete files detected as BKDR_ASNET.YVAGE. 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.

NOTES:

To remove the added accounts:

  1. Open cmd.exe
  2. Type the following:
    • net user server_sys /delete
    • net user AstNet /delete
  3. Close cmd.exe


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