Analysis by: Jasen Sumalapao
ALIASES:

Virus:Win32/Quervar.gen!B (Microsoft), W32/XDocCrypt.b (NAI), Mal/Agent-AJK (Sophos), Gen:Variant.Zbot.10 (FSecure), TR/Crypt.EPACK.Gen8 (Antivir), Gen:Variant.Zbot.10 (Bitdefender), W32/Zbot.ACM!tr (Fortinet), Trojan-Downloader.Win32.Cbeplay (Ikarus), a variant of Win32/Kryptik.AKWU trojan (NOD32)

 PLATFORM:

Windows 2000, Windows XP, Windows Server 2003

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

  • Threat Type: File infector

  • Destructiveness: No

  • Encrypted:

  • In the wild: Yes

  OVERVIEW

Infection Channel: Downloaded from the Internet, Dropped by other malware, Infects files

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

It creates folders where it drops its files. It injects its dropped file/component to specific processes.

It creates an infection marker in infected files.

  TECHNICAL DETAILS

File Size: 203,264 bytes
File Type: EXE
Memory Resident: Yes
Initial Samples Received Date: 27 Aug 2012
Payload: Connects to URLs/IPs, Drops files

Arrival Details

This file infector 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 file infector drops the following component file(s):

  • %User Profile%\Application Data\{Random Folder}\{Random File name}.EXE.LNK
  • %User Profile%\Application Data\{Random Folder}\{Random File name}.EXE.INI

(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 drops and executes the following files:

  • %User Profile%\Application Data\{Random folder}\{Random File name}.exe - detected as PE_QUERVAR.C-O

(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 creates the following folders:

  • %User Profile%\Application Data\{Random Folder}

(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 its dropped file/component to the following processes:

  • csrss.exe

It terminates itself if it finds the following processes in the affected system's memory:

  • taskmgr.exe

Autostart Technique

This file infector modifies the following registry entry(ies) to enable its automatic execution at every system startup:

HKEY_CURRENT_USER\Software\Microsoft\
Windows NT\CurrentVersion\Windows
Load = "%User Profile%\Application Data\{Random Folder}\{Random Filename}.EXE.LNK"

(Note: The default value data of the said registry entry is "".)

File Infection

This file infector infects the following file types:

  • EXE
  • DOC
  • DOCX
  • XLS
  • XLSX

It creates an infection marker in infected files.

Other Details

This file infector connects to the following possibly malicious URL:

  • http://windows{BLOCKED}soft.com/update.apx
  • http://{BLOCKED}w.com.br/includes/domit/way.php
  • http://www.{BLOCKED}kes.com/way.php

NOTES:

This file infector renames the extension of the infected file to the following:

  • .DOC to .COD.SCR
  • .DOCX to .XCOD.SCR
  • .XLS to .SLX.SCR
  • .XLSX to .XSLX.SCR

It then deletes the original copy of the infected files. The infected files are already detected by Trend Micro as PE_QUERVAR.C.

Analysis of this file infector shows that there is an error during its execution.

  SOLUTION

Minimum Scan Engine: 9.200
FIRST VSAPI PATTERN FILE: 9.352.05
FIRST VSAPI PATTERN DATE: 27 Aug 2012
VSAPI OPR PATTERN File: 9.353.00
VSAPI OPR PATTERN Date: 28 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/grayware files dropped/downloaded by PE_QUERVAR.C-O

Step 3

Scan your computer with your Trend Micro product and note files detected as PE_QUERVAR.C-O

Step 4

Restart in Safe Mode

[ Learn More ]

Step 5

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.
  • %User Profile%\Application Data\{Random Folder}

Step 6

Restore this modified 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 NT\CurrentVersion\Windows
    • From: Load = %User Profile%\Application Data\{Random Folder}\{Random File name}.EXE.LNK
      To: Load = ""

Step 7

Restart in normal mode and scan your computer with your Trend Micro product for files detected as PE_QUERVAR.C-O. 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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