WORM_RIMECUD.ZB

 Analysis by: Christopher Daniel So

 ALIASES:

Trojan:Win32/Ircbrute (Microsoft); W32.Pilleuz (Symantec); IRC-Worm.Win32.Small.jd (Kaspersky); W32/Agent.RXN!tr.dldr (Fortinet); Win32/AutoRun.KS worm (Nod32); BScope.Trojan.Aykid.23205 (VBA32)

 PLATFORM:

Windows 2000, Windows XP, Windows Server 2003

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

  • Threat Type: Worm

  • Destructiveness: No

  • Encrypted: Yes

  • In the wild: Yes

  OVERVIEW

Infection Channel:

Propagates via removable drives


This worm accesses websites to download files detected by Trend Micro as:

  • TROJ_FAKEAV.SM8
  • TROJ_RIMECUD.DL
  • WORM_RIMECUD.SMC

This worm arrives via 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 executes the downloaded files. As a result, malicious routines of the downloaded files are exhibited on the affected system.

  TECHNICAL DETAILS

File Size:

40,960 bytes

File Type:

PE

Memory Resident:

Yes

Initial Samples Received Date:

18 Feb 2011

Payload:

Downloads files

Arrival Details

This worm arrives via removable drives.

It may be downloaded from the following remote sites:

  • http://b.{BLOCKED}vel.biz/app.exe

Installation

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

  • %System Root%\RECYCLER\{random SID}\winfixer.exe

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

It drops the following files:

  • %System Root%\RECYCLER\{random SID}\Desktop.ini - nonmalicious file

(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\{random SID}

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

It stays memory-resident by injecting codes into the following processes:

  • 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\{random SID}\winfixer.exe"

Propagation

This worm drops the following copy(ies) of itself in all removable drives:

  • {drive letter}:\RECYCLER\{random SID}\winfixer.exe

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:

{random characters}
[autorun]
open=RECYCLER\{random SID}\winfixer.exe
{random characters}
icon=%System Root%\system32\SHELL32.dll,4
action=Open folder to view files
shell\open=Open
shell\open\command=RECYCLER\{random SID}\winfixer.exe
{random characters}
shell\open\default=1
{random characters}

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

Download Routine

This worm accesses the following websites to download files:

  • http://two.{BLOCKED}raoi.com/bnet.exe
  • http://b.{BLOCKED}pgirl.com/myms.exe
  • http://{BLOCKED}pgirl.com/ms0593.exe

It saves the files it downloads using the following names:

  • %User Profile%\bnt.exe
  • %User Profile%\msc.exe
  • %User Profile%\wors.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.)

Trend Micro detects the dowloaded file as:

  • TROJ_FAKEAV.SM8
  • TROJ_RIMECUD.DL
  • WORM_RIMECUD.SMC

It then executes the downloaded files. As a result, malicious routines of the downloaded files are exhibited on the affected system.

  SOLUTION

Minimum Scan Engine:

8.900

FIRST VSAPI PATTERN FILE:

7.844.09

FIRST VSAPI PATTERN DATE:

18 Feb 2011

VSAPI OPR PATTERN File:

7.845.00

VSAPI OPR PATTERN Date:

19 Feb 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

Remove malware files dropped/downloaded by WORM_RIMECUD.ZB

Step 3

Identify and delete files detected as WORM_RIMECUD.ZB using either the Startup Disk or Recovery Console

[ 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\{random SID}\winfixer.exe

Step 5

Search and delete AUTORUN.INF files created by WORM_RIMECUD.ZB that contain these strings

[ Learn More ]
{random characters}
[autorun]
open=RECYCLER\{random SID}\winfixer.exe
{random characters}
icon=%System Root%\system32\SHELL32.dll,4
action=Open folder to view files
shell\open=Open
shell\open\command=RECYCLER\{random SID}\winfixer.exe
{random characters}
shell\open\default=1
{random characters}

Step 6

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\{random SID}

Step 7

Scan your computer with your Trend Micro product to delete files detected as WORM_RIMECUD.ZB. 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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