Modified by: Sabrina Lei Sioting

ALIASES:

Troj/Cosmu-O (Sophos) ,W32/Cosmu.ANHF!tr (Fortinet) ,Trojan.Win32.Cosmu (Ikarus) ,Trojan:Win32/Msposer.E (Microsoft) ,pws-ja!cg (McAfee) ,Win32/VB.NAX virus (Eset) ,Trojan.Gen (Symantec) ,Trj/Sinowal.WWG (Panda) ,Trojan.Win32.Generic!BT (Sunbelt)

 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:
 INFORMATION EXPOSURE:

  • Threat Type: File infector

  • Destructiveness: No

  • Encrypted: Yes

  • In the wild: Yes

  OVERVIEW

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

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.

  TECHNICAL DETAILS

File Size: Varies
File Type: EXE
Memory Resident: Yes
Initial Samples Received Date: 05 Oct 2012
Payload: 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 copies of itself into the affected system:

  • %System%\winword.exe
  • %System%\ctfmoon.exe

(Note: %System% is the Windows system folder, which is usually C:\Windows\System32.)

It adds the following processes:

  • %System%\winword.exe

(Note: %System% is the Windows system folder, which is usually C:\Windows\System32.)

It leaves the following text files:

  • {Malware Path}\chor.txt - if the System date is May 11

Autostart Technique

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

HKEY_CURRENT_USER\Software\Microsoft\
Windows\CurrentVersion\Run
ctfmoon.exe = "%System%\Com\ctfmoon.exe"

HKEY_LOCAL_MACHINE\Software\Microsoft\
Windows\CurrentVersion\Run
AUTOWORD = "%System%\winword.exe"

File Infection

This file infector infects the following files:

  • *.doc
  • *.docx

NOTES:

It monitors the following Window Class & Title:

  • ExploreWClass
  • WorkerA
  • WorkerW
  • ReBarWindow32
  • ComboBoxEx32
  • ComboBox
  • Edit
  • IEFrame
  • Navigation Bar
  • Address and Band Root

It then obtains the value inputted as this will be used as a directory where it will search for .DOC and .DOCX files that it will try to infect.

It saves a copy of the encrypted target file in the %System% folder as {document filename}.enc.

It encrypts the target files before prepending a copy of itself. The file extension is also changed to .EXE.

  SOLUTION

Minimum Scan Engine: 9.700
VSAPI OPR PATTERN File: 9.443.00
VSAPI OPR PATTERN Date: 05 Oct 2012

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 terminate files detected as PE_COSVAR.A-O

[ Learn More ]
  1. Windows Task Manager may not display all running processes. In this case, please use a third-party process viewer, preferably Process Explorer, to terminate the malware/grayware/spyware file. You may download the said tool here.
  2. If the detected file is displayed in either Windows Task Manager or Process Explorer but you cannot delete it, restart your computer in safe mode. To do this, refer to this link for the complete steps.
  3. If the detected file is not displayed in either Windows Task Manager or Process Explorer, continue doing the next steps.

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_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Run
    • ctfmoon.exe = "%System%\Com\ctfmoon.exe"
  • In HKEY_LOCAL_MACHINE\Software\Microsoft\Windows\CurrentVersion\Run
    • AUTOWORD = "%System%\winword.exe"

Step 4

Search and delete this file

[ Learn More ]
There may be some 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. {Malware Path}\Chor.txt
%System$\{document filename}.enc

Step 5

Scan your computer with your Trend Micro product to delete files detected as PE_COSVAR.A-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.

NOTES:

Users may also visit the link provided below for the corresponding fixtool for this detection:


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