Modified by: Jasen Sumalapao
ALIASES:

Trojan.Win32.Agent.tmhv (Kaspersky), Gen:Variant.Zusy.4398 (Bitdefender)

 PLATFORM:

Windows 2000, Windows XP, Windows Server 2003

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

  • Threat Type: Trojan

  • Destructiveness: No

  • Encrypted: No

  • In the wild: Yes

  OVERVIEW

Infection Channel: Dropped by other malware

This Trojan attempts to replace a system file with a copy of itself. This results to the crash of the affected computer.

This Trojan may be dropped by other malware.

It deletes itself after execution.

  TECHNICAL DETAILS

File Size: 29,696 bytes
Memory Resident: Yes
Initial Samples Received Date: 24 Aug 2012
Payload: Modifies files

Arrival Details

This Trojan may be dropped by the following malware:

  • TROJ_ARTIEF.BWZ

Installation

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

  • %System%\lsass.exe

(Note: %System% is the Windows system folder, which is usually C:\Windows\System on Windows 98 and ME, C:\WINNT\System32 on Windows NT and 2000, or C:\Windows\System32 on Windows XP and Server 2003.)

Autostart Technique

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

HKEY_CURRENT_USER\Software\Microsoft\
Windows\CurrentVersion\Run
lsass.exe = %System%\lsass.exe

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\
Control\Session Manager
PendingFileRenameOperations = @\??\%System%\@%System%\lsass.exe.tmp

Other Details

This Trojan deletes itself after execution.

NOTES:

This Trojan attempts to replace the system file %System%\lsass.exe with a copy of itself. This results to the crash of the affected computer.

  SOLUTION

Minimum Scan Engine: 9.200
FIRST VSAPI PATTERN FILE: 9.346.08
FIRST VSAPI PATTERN DATE: 24 Aug 2012
VSAPI OPR PATTERN File: 9.347.00
VSAPI OPR PATTERN Date: 25 Aug 2012

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_INJECT.BWZ

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_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Run
    • lsass.exe = "%System%\lsass.exe"
  • In HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\Session Manager
    • PendingFileRenameOperations = "@\??\%System%\@%System%\lsass.exe.tmp"

Step 5

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