Analysis by: Marfel Tiamzon
ALIASES:

W32/Refroso.ATR!tr (Fortinet)

 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 has certain capabilities.

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 Internet Relay Chat (IRC) servers. It executes commands from a remote malicious user, effectively compromising the affected system.

  TECHNICAL DETAILS

File Size: 85,632 bytes
Memory Resident: Yes
Initial Samples Received Date: 30 Sep 2011
Payload: Terminates processes, 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.

Installation

This backdoor drops the following copies of itself into the affected system:

  • %User Temp%\HKCwin32.exe

(Note: %User Temp% is the current user's Temp folder, which is usually C:\Documents and Settings\{user name}\Local Settings\Temp 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:

  • ASKDhf2y928SDHasl

It is injected into the following processes running in memory:

  • csrss.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
HotKeysCommands = %User Temp%\HKCwin32.exe

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\
Windows\CurrentVersion\Run
HotKeysCommands = %User Temp%\HKCwin32.exe

Backdoor Routine

This backdoor opens the following port(s) where it listens for remote commands:

  • TCP Port 6969

It connects to any of the following Internet Relay Chat (IRC) servers:

  • {BLOCKED}as.{BLOCKED}a2011.com
  • {BLOCKED}lz.edu

It joins any of the following IRC channel(s):

  • #spmx

It executes the following commands from a remote malicious user:

  • clean
  • update
  • removeo
  • unsort
  • protleave
  • adware
  • torrent

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

  • http://{BLOCKED}s.{BLOCKED}roba.jp

Dropping Routine

This backdoor sets the attributes of its dropped file(s) to the following:

  • System
  • Hidden
  • Read Only

NOTES:

It has the following backdoor capabilities:

  • Execute and terminate process
  • Download files
  • Update itself
  • Clean remnants of itself

  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

Scan your computer with your Trend Micro product and note files detected as BKDR_VB.AZI

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
    • HotKeysCommands "%User Temp%\HKCwin32.exe"
  • In HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Run
    • HotKeysCommands "%User Temp%\HKCwin32.exe"

Step 5

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