Analysis by: Sabrina Lei Sioting
ALIASES:

TrojanDownloader:Win32/Chksyn.gen!A (Microsoft); Trojan-Downloader.Win32.Agent.azg (Kaspersky); Trojan.AVKiller.AW (Fsecure); Trojan.Win32.Packer.BlackEnergyDDoSBotCrypter (Sunbelt); Backdoor.Win32.Kbot.aq (Ikarus)

 PLATFORM:

Windows 2000, Windows XP, Windows Server 2003

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

  • 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.

  TECHNICAL DETAILS

File Size: 11,047 bytes
Memory Resident: Yes
Initial Samples Received Date: 05 Mar 2010

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 copies of itself into the affected system:

  • %System%\vhosts.exe

(Note: %System% is the Windows system folder, which is usually C:\Windows\System on Windows 98 and ME, C:\WINNT\System32 on Windows NT and 2000, or C:\Windows\System32 on Windows XP and Server 2003.)

Autostart Technique

This backdoor registers itself as a system service to ensure its automatic execution at every system startup by adding the following registry entries:

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\
Services\msupdate
ImagePath = "%System%\vhosts.exe"

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\
Services\msupdate
DisplayName = "Microsoft security update service"

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\
Services\msupdate
Description = "This service downloading and installing Windows security updates"

Other System Modifications

This backdoor adds the following registry keys as part of its installation routine:

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\
Services\msupdate

Other Details

This backdoor connects to the following possibly malicious URL:

  • http://{BLOCKED}herbalsinc.com/so/stat.php

  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. Before you could do this, you must restart in Safe Mode. For instructions on how to do this, you may refer to this page If the preceding step requires you to restart in safe mode, you may proceed to edit the system registry.

 
  • In HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services
    • msupdate

Step 4

Scan your computer with your Trend Micro product to delete files detected as BKDR_PROXY.SLS. 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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