WORM_REFROSO.WN

October 08, 2012
 Analysis by: kathleenno
 ALIASES:

W32.IRCBot (Symantec); VirTool:Win32/Injector.gen!AD (Microsoft); Trojan-Downloader.Win32.Refroso.avp (Kaspersky); BackDoor-EEF (Mcafee)

 PLATFORM:

Windows 2000, Windows XP, Windows Server 2003

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

  • Threat Type: Worm

  • Destructiveness: No

  • Encrypted: No

  • In the wild: Yes

  OVERVIEW

Infection Channel:

Propagates via removable drives

This worm arrives via removable drives. It arrives on a system as a file dropped by other malware or as a file downloaded unknowingly by users when visiting malicious sites.

It drops copies of itself in all removable drives. It drops an AUTORUN.INF file to automatically execute the copies it drops when a user accesses the drives of an affected system.

It connects to a website to send and receive information.

  TECHNICAL DETAILS

File Size:

7,844,864 bytes

File Type:

EXE

Memory Resident:

Yes

Initial Samples Received Date:

19 Apr 2011

Payload:

Compromises system security, Drops files

Arrival Details

This worm arrives via removable drives.

It 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 worm drops the following non-malicious files:

  • %System Root%\RECYCLER\{SID}\Desktop.ini

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

It drops the following copies of itself into the affected system:

  • %System Root%\RECYCLER\{SID}\rundll32.exe

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

It creates the following folders:

  • %System Root%\RECYCLER\{SID}

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

It injects itself into the following processes as part of its memory residency routine:

  • explorer.exe

Autostart Technique

This worm adds the following registry entries to enable its automatic execution at every system startup:

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\
Windows NT\CurrentVersion\Winlogon
Taskman = %System Root%\RECYCLER\{SID}\rundll32.exe

Propagation

This worm drops copies of itself in all removable drives.

It drops an AUTORUN.INF file to automatically execute the copies it drops when a user accesses the drives of an affected system.

The said .INF file contains the following strings:

;{garbage characters}
[autorun
:jmp0
open={folder name}\{random filename}.exe
:nop
icon=%SystemRoot%\system32\SHELL32.dll,4
;{garbage characters}
action=Open folder to view files using Windows Explorer
;{garbage characters}
shell\\\open\\\command={folder name}/{random filename}.exe
shell\\explore\\\command={folder name}/{random filename}.exe
useautoplay=1
[AutoRun]
;{garbage characters}
:GOTO NUL

Backdoor Routine

This worm connects to the following websites to send and receive information:

  • {BLOCKED}ws.org

Dropping Routine

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

  • Hidden
  • Read Only
  • System

NOTES:

It checks for the following:

  • - if the malware filename is C:\sample.exe or C:\windows\system32\sample_1.exe
  • - if the username is currentuser
  • - if the following window names exist:
  • The Wireshark Network Analyzer
  • Process Monitor - Sysinternals: www.sysinternals.com
  • File Monitor - Sysinternals: www.sysinternals.com
  • Registry Monitor - Sysinternals: www.sysinternals.com

  SOLUTION

Minimum Scan Engine:

8.900

FIRST VSAPI PATTERN FILE:

7.990.06

FIRST VSAPI PATTERN DATE:

19 Apr 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 WORM_REFROSO.WN

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_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows NT\CurrentVersion\Winlogon
    • Taskman = %System Root%\RECYCLER\{SID}\rundll32.exe

Step 5

Search and delete these folders

[ Learn More ]
Please make sure you check the Search Hidden Files and Folders checkbox in the More advanced options option to include all hidden folders in the search result.

%System Root%\RECYCLER\{SID}

Step 6

Search and delete AUTORUN.INF files created by WORM_REFROSO.WN that contain these strings

[ Learn More ]



;{garbage characters}
[autorun
:jmp0
open={folder name}\{random filename}.exe
:nop
icon=%SystemRoot%\system32\SHELL32.dll,4
;{garbage characters}
action=Open folder to view files using Windows Explorer
;{garbage characters}
shell\\open\\command={folder name}/{random filename}.exe
shell\explore\\command={folder name}/{random filename}.exe
useautoplay=1
[AutoRun]
;{garbage characters}
:GOTO NUL

Step 7

Scan your computer with your Trend Micro product to delete files detected as WORM_REFROSO.WN. 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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