Analysis by: Christopher Daniel So

ALIASES:

Trojan:Win32/Rimecud.A (Microsoft), W32/Rimecud.gen.ax (McAfee)

 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 arrives by connecting affected removable drives to a system.

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

  TECHNICAL DETAILS

File Size: Varies
File Type: EXE
Memory Resident: Yes
Initial Samples Received Date: 29 Apr 2011
Payload: Connects to URLs/IPs

Arrival Details

This worm arrives by connecting affected removable drives to a system.

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:\Documents and Settings\{user name} on Windows 2000, XP, and Server 2003, or C:\Users\{user name} on Windows Vista and 7.)

It adds the following mutexes to ensure that only one of its copies runs at any one time:

  • 5{bR+10

It stays resident in memory by creating the following process(es):

  • svchost.exe

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

  • 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:

  • seksw

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

  • seksw\tempomat.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=seksw//tempomat.exe
Shell\do\nothing
~ouIIIIIIIIIIIIIIIIII
icon=seksw//tempomat.exe
open=seksw//tempomat.exe
action=Open folder to see files using Windows Explorer
shell\\\\\\Open\\\\\\command=seksw//tempomat.exe
shell\\\\\\Explore\\\\\\command=seksw//tempomat.exe

Backdoor Routine

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

  • {BLOCKED}na.{BLOCKED}olic.su
  • {BLOCKED}er.{BLOCKED}losarske.ru
  • {BLOCKED}ke.{BLOCKED}arke.com
  • {BLOCKED}ce.{BLOCKED}racala.org

  SOLUTION

Minimum Scan Engine: 8.900
FIRST VSAPI PATTERN FILE: 8.126.08
FIRST VSAPI PATTERN DATE: 29 Apr 2011

Step 1

Before doing any scans, Windows XP, Windows Vista, and Windows 7 users must disable System Restore to allow full scanning of their computers.

Step 2

Identify and delete files detected as WORM_PALEVO.SMAG using either the Startup Disk or Recovery Console

[ 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 this folder

[ 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 letter}:\seksw

Step 5

Search and delete AUTORUN.INF files created by WORM_PALEVO.SMAG that contain these strings

[ Learn More ]


[AutoRun]
USEAUTOPLAY=1
shellexecute=seksw//tempomat.exe
Shell\do\nothing
~ouIIIIIIIIIIIIIIIIII
icon=seksw//tempomat.exe
open=seksw//tempomat.exe
action=Open folder to see files using Windows Explorer
shell\\\Open\\\command=seksw//tempomat.exe
shell\\\Explore\\\command=seksw//tempomat.exe

Step 6

Scan your computer with your Trend Micro product to delete files detected as WORM_PALEVO.SMAG. 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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