Analysis by: Roland Marco Dela Paz
ALIASES:

Trojan:Win32/Rimecud.A (Microsoft); Trojan.Win32.Sasfis.bdxz (Kaspersky)

 PLATFORM:

Windows 2000, Windows XP, Windows Server 2003

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

  • Threat Type: Trojan

  • Destructiveness: No

  • Encrypted: Yes

  • In the wild: Yes

  OVERVIEW

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

  TECHNICAL DETAILS

File Size: 76,288 bytes
File Type: PE
Memory Resident: Yes
Initial Samples Received Date: 25 Jan 2011
Payload: Downloads files

Installation

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

  • %User Profile%\fxmdk.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 Trojan 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%\fxmdk.exe"

Download Routine

This Trojan accesses the following websites to download files:

  • http://{BLOCKED}1.{BLOCKED}1.175.219:59171/lnubvcre - detected as TROJ_INJECT.SMD
  • http://{BLOCKED}e.vn/malin.exe - detected as TROJ_INJECT.QWZQ

It saves the files it downloads using the following names:

  • %User Temp%\{random number1}.exe
  • %User Temp%\{random number2}.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 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: 7.792.10
FIRST VSAPI PATTERN DATE: 25 Jan 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 TROJ_SASFIS.HQ

Step 3

Since this malware uses rootkit technology, detection and removal using normal and safe mode methods may not eliminate it completely. This procedure restarts the system using the Windows Recovery Console.

  1. Insert the Windows Installation CD into the CD drive, then Press the restart button.
  2. Upon prompt, press any key to boot from the CD.
  3. On the main menu, type r to go to the Recovery Console.
  4. Type the drive that contains Windows (usually C:) and press Enter.
  5. In the input box, type the following then press Enter:
    • %User Profile%\fxmdk.exe
  6. Type exit and press Enter to restart the system normally.

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 = %User Profile%\fxmdk.exe

Step 5

Scan your computer with your Trend Micro product to delete files detected as TROJ_SASFIS.HQ. 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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