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BKDR_ASNET.DNF

December 30, 2014
 Analysis by: Rika Joi Gregorio
 ALIASES:

W32/Autoit.NQO!tr(Fortinet), Trojan.Win32.Autoit(Ikarus), Win32/Autoit.NQO trojan(Eset)

 PLATFORM:

Windows

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

  • Threat Type: Backdoor

  • Destructiveness: No

  • Encrypted: Yes

  • In the wild: Yes

  OVERVIEW

Infection Channel:

Downloaded from the Internet

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:

431,616 bytes

File Type:

EXE

Memory Resident:

Yes

Initial Samples Received Date:

08 Dec 2014

Payload:

Connects to URLs/IPs, Downloads files

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.

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:

  • www.{BLOCKED}shoes.jp/contents/images/spacer5.gif - based from configuration file

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

  • www.{BLOCKED}u.com.my/images/history5.jpg

It saves the files it downloads using the following names:

  • %User Temp%\andords.ini - configuration file
  • %User Temp%\emmo32.exe - detected as TROJ_CRYPTED.SMA

(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.

Information Theft

This backdoor s configuration file contains the following information:

  • Download link of arbitrary file

Other Details

This backdoor adds the following accounts to the Administrator group:

  • server_sys
  • AstNet

  SOLUTION

Minimum Scan Engine:

9.700

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.DNF. (Note: Please skip this step if the threats listed below have already been removed.)

     
    • TROJ_CRYPTED.SMA

Step 4

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

Step 5

Terminate a process file/s detected as BKDR_ASNET.DNF

[ Learn More ]

*Note: If the detected file/s is/are not displayed in theWindows Task Manager, 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.
  • %User Temp%\andords.ini

Step 8

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

Remove the accounts added by this spyware. To remove the added accounts:

  1. Open the command prompt. Click the Windows logo. In the Search program and files bar, type cmd.exe and press Enter.
  2. In the command prompt, type the following:
    net user server_sys /delete
    net user AstNet /delete
  3. Close the command prompt.


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