Worm.Win32.CHESTBD.A

October 17, 2018
 Analysis by: Carl Maverick Pascual
 ALIASES:

Trojan:Win32/Occamy.C (Microsoft) ; HEUR:Trojan-Dropper.Win32.Generic (Kaspersky)

 PLATFORM:

Windows

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

  • Threat Type: Worm

  • Destructiveness: No

  • Encrypted: No

  • In the wild: Yes

  OVERVIEW

Infection Channel:

Dropped by other malware, Downloaded from the Internet

This Worm 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:

976,384 bytes

File Type:

EXE

Memory Resident:

No

Initial Samples Received Date:

10 Oct 2018

Payload:

Drops files

Arrival Details

This Worm 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 Worm drops the following files:

  • %Application Data%\Xå8+Ö -> Detected as Trojan.Win32.CHESTBD.A
  • %Application Data%\Xå8+Ö.zip - Deleted Afterwards
  • %System%\dllcache\sethc.exe -> Detected as Trojan.Win32.CHESTBD.A
  • %System%\sethc.exe -> Detected as Trojan.Win32.CHESTBD.A

(Note: %Application Data% is the current user's Application Data folder, which is usually C:\Documents and Settings\{user name}\Application Data on Windows 2000, XP, and Server 2003, or C:\Users\{user name}\AppData\Roaming on Windows Vista, 7, and 8.. %System% is the Windows system folder, where it usually is C:\Windows\System32 on all Windows operating system versions.)

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

  • {Drive C to Z}:\Gato.jpg .exe
  • %Application Data%\{malware file name}.exe

(Note: %Application Data% is the current user's Application Data folder, which is usually C:\Documents and Settings\{user name}\Application Data on Windows 2000, XP, and Server 2003, or C:\Users\{user name}\AppData\Roaming on Windows Vista, 7, and 8.)

Autostart Technique

This Worm drops the following shortcut pointing to its copy in the User Startup folder to enable its automatic execution at every system startup:

  • %User Startup%\Gato.lnk -> Target file: %Application Data%\{malware file name}.exe

(Note: %Application Data% is the current user's Application Data folder, which is usually C:\Documents and Settings\{user name}\Application Data on Windows 2000, XP, and Server 2003, or C:\Users\{user name}\AppData\Roaming on Windows Vista, 7, and 8.)

Other Details

This Worm does the following:

  • It propagates on drives (From C:\ to Z:\) present on the infected machine when the drive is either being Inserted into or Ejected from the infected machine.

  SOLUTION

Minimum Scan Engine:

9.850

FIRST VSAPI PATTERN FILE:

14.568.02

FIRST VSAPI PATTERN DATE:

16 Oct 2018

VSAPI OPR PATTERN File:

14.569.00

VSAPI OPR PATTERN Date:

17 Oct 2018

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

Note that not all files, folders, and registry keys and entries are installed on your computer during this malware's/spyware's/grayware's execution. This may be due to incomplete installation or other operating system conditions. If you do not find the same files/folders/registry information, please proceed to the next step.

Step 3

Identify and terminate files detected as Worm.Win32.CHESTBD.A

[ 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 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.
  • {Drive C to Z}:\Gato.jpg                                                                 .exe
  • %System%\dllcache\sethc.exe
  • %System%\sethc.exe
  • %Application Data%\{malware file name}.exe
  • %Application Data%\Xå8+Ö
  • %Application Data%\Xå8+Ö.zip
  • %User Startup%\Gato.lnk

Step 5

Scan your computer with your Trend Micro product to delete files detected as Worm.Win32.CHESTBD.A. 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 the following Trend Micro Support pages for more information:


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