WORM_RIMECUD.CY

October 08, 2012
 Analysis by: jasperm
 ALIASES:

Microsoft: Backdoor:Win32/Small.Z; Authentium: W32/SmallTrojan.V.gen!Eldorado

 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

This worm arrives via removable drives. It may be dropped by other malware. It may be unknowingly downloaded by a user while visiting malicious websites.

It drops copies of itself into all the removable drives connected to an affected system. 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:

171,008 bytes

File Type:

PE

Memory Resident:

Yes

Initial Samples Received Date:

08 Feb 2011

Arrival Details

This worm arrives via removable drives.

It may be dropped by other malware.

It may be unknowingly downloaded by a user while visiting malicious websites.

Installation

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

  • %User Profile%\ydwzro.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 injects codes into the following process(es):

  • SVCHOST.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 = %User Profile%\ydwzro.exe

Propagation

This worm creates the following folders in all removable drives:

  • stakleni

It drops copies of itself into all the removable drives connected to an affected system.

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

  • stakleni\dah.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:

[autorun]
USEAUTOPLAY=1
shellexecute={malware path and file name}.exe
Shell\do\nothing
icon={malware path and file name}.exe
open={malware path and file name}.exe
action=Open folder to see files using Windows Explorer
shell\Open\command={malware path and file name}.exe
shell\Explorer\command={malware path and file name}.exe

Backdoor Routine

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

  • {BLOCKED}a.{BLOCKED}olic.su
  • {BLOCKED}r.{BLOCKED}losarske.ru
  • {BLOCKED}e.{BLOCKED}arke.com
  • {BLOCKED}e.{BLOCKED}bracala.org

  SOLUTION

Minimum Scan Engine:

8.900

VSAPI PATTERN File:

under testing

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

Restart in Safe Mode

[ Learn More ]

Step 3

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 = %User Profile%\ydwzro.exe

Step 4

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. {removable drive}:\stakleni

Step 5

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

[ Learn More ]
 [autorun]
USEAUTOPLAY=1
shellexecute={malware path and file name}.exe
Shell\do\nothing
icon={malware path and file name}.exe
open={malware path and file name}.exe
action=Open folder to see files using Windows Explorer
shell\Open\command={malware path and file name}.exe
shell\Explorer\command={malware path and file name}.exe

Step 6

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