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BKDR_ASPER.AU

October 12, 2012
 ALIASES:

TrojanDownloader:Win32/Fakr.B (Microsoft); Trojan.Gen (Symantec); Backdoor.Win32.Asper.sxl (Kaspersky); Trojan.Win32.Generic!BT (Sunbelt); Trojan.Generic.7253000 (FSecure)

 PLATFORM:

Windows 2000, Windows XP, Windows Server 2003

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

  • Threat Type: Backdoor

  • Destructiveness: No

  • Encrypted:

  • 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.

  TECHNICAL DETAILS

File Size:

1,206,272 bytes

File Type:

EXE

Memory Resident:

Yes

Initial Samples Received Date:

03 Apr 2012

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.

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
subjet = "%Program Files%\subjet\subjete.exe"

Other System Modifications

This backdoor deletes the following files:

  • %System Root%\old_subjete.exe

(Note: %System Root% is the root folder, which is usually C:\. It is also where the operating system is located.)

It adds the following registry keys:

HKEY_CURRENT_USER\Software\subjet

It deletes the following registry keys:

HKEY_CURRENT_USER\Software\Microsoft\
Windows\CurrentVersion\Ext\
Settings\{7B1F1AE7-7B63-487E-8F45-1471E1BD826E}

HKEY_CURRENT_USER\Software\Microsoft\
Windows\CurrentVersion\Ext\
Settings\{B94B232A-6207-46BB-B116-60B3B6267D83}

Dropping Routine

This backdoor drops the following files:

  • %System Root%\subjet_conifg.ini
  • %System Root%\subjet.dll

(Note: %System Root% is the root folder, which is usually C:\. It is also where the operating system is located.)

This report is generated via an automated analysis system.

  SOLUTION

Minimum Scan Engine:

9.200

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

Restart in Safe Mode

[ Learn More ]

Step 3

Delete this registry key

[ 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
    • subjet

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
    • subjet = "%Program Files%\subjet\subjete.exe"

Step 5

Search and delete these files

[ 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.
  • %System Root%\subjet_conifg.ini
  • %System Root%\subjet.dll

Step 6

Restart in normal mode and scan your computer with your Trend Micro product for files detected as BKDR_ASPER.AU. 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 this file from backup only Microsoft-related files will be restored. If this malware/grayware also deleted files related to programs that are not from Microsoft, please reinstall those programs on you computer again.

  • %System Root%\old_subjete.exe

Step 8

Restore these deleted registry keys/values from backup

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

  • In HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Ext\Settings
    • {7B1F1AE7-7B63-487E-8F45-1471E1BD826E}
  • In HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Ext\Settings
    • {B94B232A-6207-46BB-B116-60B3B6267D83}


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