TROJ_DROPPER.ZOL

July 30, 2013
 Analysis by: Jennifer Gumban
 ALIASES:

Trojan-Dropper.Win32.Sysn.qda (Kaspersky), Trojan:Win32/Claretore.H (Microsoft)

 PLATFORM:

Windows 2000, Windows Server 2003, Windows XP (32-bit, 64-bit), Windows Vista (32-bit, 64-bit), Windows 7 (32-bit, 64-bit)

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

  • Threat Type: Trojan

  • Destructiveness: No

  • Encrypted:

  • In the wild: Yes

  OVERVIEW

This Trojan arrives on a system as a file dropped by other malware or as a file downloaded unknowingly by users when visiting malicious sites.

  TECHNICAL DETAILS

File Size:

65,536 bytes

File Type:

EXE

Memory Resident:

No

Initial Samples Received Date:

23 Jul 2013

Arrival Details

This Trojan arrives on a system as a file dropped by other malware or as a file downloaded unknowingly by users when visiting malicious sites.

Installation

This Trojan drops the following file(s)/component(s):

  • %TEMP%\{Random File Name 3}.tmp
  • %TEMP%\{Random File Name 2}-0.tmp

It drops the following copies of itself into the affected system:

  • %User Profile%\{Random File Name 1 }-0.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.)

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
Windows Update Server = "%User Profile%\{Random File Name 1}-0.exe"

Other System Modifications

This Trojan adds the following registry entries:

HKEY_LOCAL_MACHINE\SYSTEM\{Current Control Set}\
Control\Session Manager
PendingFileRenameOperations = "\??\%TEMP%\{Random File Name 2}-0.tmp , , \??\{Initial File Path}\{Initial File Name}, "

  SOLUTION

Minimum Scan Engine:

9.300

FIRST VSAPI PATTERN FILE:

10.178.03

FIRST VSAPI PATTERN DATE:

26 Jul 2013

VSAPI OPR PATTERN File:

10.179.00

VSAPI OPR PATTERN Date:

27 Jul 2013

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

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
    • Windows Update Server = "%User Profile%\{Random File Name 1}-0.exe"
  • In HKEY_LOCAL_MACHINE\SYSTEM\{Current Control Set}\Control\Session Manager
    • PendingFileRenameOperations = "\??\%TEMP%\{Random File Name 2}-0.tmp , , \??\{Initial File Path}\{Initial File Name}, "

Step 3

Search and delete these files

[ Learn More ]
There may be some component files that are hidden. Please make sure you check the Search Hidden Files and Folders checkbox in the More advanced options option to include all hidden files and folders in the search result.
  • %TEMP%\{Random File Name 3}.tmp
  • %TEMP%\{Random File Name 2}-0.tmp

Step 4

Scan your computer with your Trend Micro product to delete files detected as TROJ_DROPPER.ZOL. 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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