BKDR_SIMBOT.SMXB

 Analysis by: Karl Dominguez

 ALIASES:

Backdoor.Trojan (Symantec); Backdoor:Win32/Simbot.gen (Microsoft); Backdoor.Win32.Agent.bwtk (Kaspersky); Generic BackDoor!dtr (Mcafee); Mal/Simbot-A (Sophos)

 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.

It connects to certain websites to send and receive information. It deletes the initially executed copy of itself.

  TECHNICAL DETAILS

File Size:

32,768 bytes

Memory Resident:

Yes

Initial Samples Received Date:

22 Nov 2011

Payload:

Connects to URLs/IPs

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:

  • %User Profile%\Local Settings\{random service name}.exe

(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 processes:

  • svchost.exe

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
{random service name} = "%User Profile%\Local Settings\{random service name}.exe"

Other Details

This backdoor connects to the following website to send and receive information:

  • http://{BLOCKED}.{BLOCKED}.222.6:80/{five random letters}.php?id={18 random characters}
  • http://{BLOCKED}.{BLOCKED}.222.6:443/{five random letters}.php?id={18 random characters}
  • http://{BLOCKED}ebook.345.pl:80/{five random letters}.php?id={18 random characters}
  • http://{BLOCKED}ebook.345.pl:443/{five random letters}.php?id={18 random characters}

It deletes the initially executed copy of itself

NOTES:

It injects codes into its created process SVCHOST.EXE. It enumerates the services in the affected system and uses a random name from the said list for its dropped copy. It may perform the following:

  • Download and save files in %User Temp%
  • Execute downloaded files

  SOLUTION

Minimum Scan Engine:

9.200

VSAPI OPR PATTERN File:

8.591.00

VSAPI OPR PATTERN Date:

22 Nov 2011

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

Scan your computer with your Trend Micro product and note files detected as BKDR_SIMBOT.SMXB

Step 3

Restart in Safe Mode

[ Learn More ]

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
    • {random service name} = "%User Profile%\Local Settings\{random service name}.exe"

Step 5

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