Analysis by: Jasen Sumalapao
ALIASES:

Backdoor:Win32/Simbot (Microsoft), DeepScan:Generic.Malware.SVdld!.7C8060FE (FSecure), DeepScan:Generic.Malware.SVdld!.7C8060FE (Bitdefender)

 PLATFORM:

Windows 2000, Windows XP, Windows Server 2003

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

  • Threat Type: Backdoor

  • Destructiveness: No

  • Encrypted: No

  • In the wild: Yes

  OVERVIEW

Infection Channel: Downloaded from the Internet, Dropped by other malware

This backdoor may be downloaded by other malware/grayware/spyware from remote sites. It may be dropped by other malware.

It executes the dropped file(s). As a result, malicious routines of the dropped files are exhibited on the affected system.

As of this writing, the said sites are inaccessible.

  TECHNICAL DETAILS

File Size: 12,800 bytes
File Type: EXE, DLL
Memory Resident: Yes
Initial Samples Received Date: 23 Aug 2012
Payload: Connects to URLs/IPs, Drops files, Downloads files

Arrival Details

This backdoor may be downloaded by other malware/grayware/spyware from remote sites.

It may be dropped by the following malware:

  • TROJ_ARTIEF.AX

Installation

This backdoor drops the following component file(s):

  • %User Profile%\ntuser.cfg - detected as BKDR_SIMBOT.AX

(Note: %User Profile% is the current user's profile folder, which is usually C:\Windows\Profiles\{user name} on Windows 98 and ME, C:\WINNT\Profiles\{user name} on Windows NT, and C:\Documents and Settings\{user name} on Windows 2000, XP, and Server 2003.)

It adds the following mutexes to ensure that only one of its copies runs at any one time:

  • NTUserCfg
  • efcc ilitat

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
NTUCF = "rundll32 %User Profile%\ntuser.cfg,Config"

Backdoor Routine

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

  • {BLOCKED}.{BLOCKED}.247.57:80

Dropping Routine

This backdoor executes the dropped file(s). As a result, malicious routines of the dropped files are exhibited on the affected system.

Download Routine

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

  • http://ssl.{BLOCKED}3.org/images/dw.html
  • http://ssl.{BLOCKED}3.org/images/fc.asp
  • http://ssl.{BLOCKED}3.org/images/pma.pdf

As of this writing, the said sites are inaccessible.

  SOLUTION

Minimum Scan Engine: 9.200
FIRST VSAPI PATTERN FILE: 9.346.01
FIRST VSAPI PATTERN DATE: 24 Aug 2012
VSAPI OPR PATTERN File: 9.347.00
VSAPI OPR PATTERN Date: 25 Aug 2012

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

Remove malware/grayware files that dropped/downloaded BKDR_SIMBOT.AX

Step 3

Restart in Safe Mode

[ Learn More ]

Step 4

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\Microsoft\Windows\CurrentVersion\Run
    • NTUCF = "rundll32 %User Profile%\ntuser.cfg,Config"

Step 5

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