WORM_FLASHBOT.A

 Analysis by: Anthony Joe Melgarejo

 ALIASES:

Worm:Win32/Pimybot.A (Microsoft), W32.SillyFDC (Symantec), Win32/Flashbot.A worm (ESET), Troj/Dapato-AI (Sophos)

 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: Worm

  • Destructiveness: No

  • Encrypted: No

  • In the wild: Yes

  OVERVIEW

Infection Channel:

Dropped by other malware, Downloaded from the Internet, Propagates via removable drives


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.

It uses Windows Task Scheduler to create a scheduled task that executes the dropped copy.

It executes commands from a remote malicious user, effectively compromising the affected system.

As of this writing, the said sites are inaccessible.

  TECHNICAL DETAILS

File Size:

562,688 bytes

File Type:

EXE

Memory Resident:

No

Initial Samples Received Date:

13 Aug 2013

Payload:

Compromises system security

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 copies of itself into the affected system and executes them:

  • %Application Data%\{random}.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 and 7.)

It drops the following files:

  • %Windows%\Tasks\FlashDrv.job - Task scheduler

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

It uses Windows Task Scheduler to create a scheduled task that executes the dropped copy.

It adds the following mutexes to ensure that only one of its copies runs at any one time:

  • iwqfhqowrfj9483urh8yfhwd9qh8qfhryhuvnkvu4h8w43rh34whf83qfh4389hf893

Autostart Technique

The scheduled task executes the malware every:

  • User logon

Other System Modifications

This worm adds the following registry keys:

HKEY_CURRENT_USER\syscheck

It adds the following registry entries:

HKEY_CURRENT_USER\syscheck
Checked = "1"

Propagation

This worm drops the following copy(ies) of itself in all removable drives:

  • {drive letter}:\RCX{random value}.tmp
  • {drive letter}:\RCX{random value}.exe

Backdoor Routine

This worm executes the following commands from a remote malicious user:

  • Receives parameters to be used to execute the downloaded file
  • Delete and/or copy itself to arbitrary directories

It connects to the following URL(s) to send and receive commands from a remote malicious user:

  • http://{BLOCKED}o.co.za/admin/st.php

It posts the following information to its command and control (C&C) server:

  • Infection log/status

Download Routine

This worm connects to the following website(s) to download and execute a malicious file:

  • http://{BLOCKED}o.co.za/admin/1.exe

It saves the files it downloads using the following names:

  • %User Temp%\fdg{random}.tmp.exe

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

As of this writing, the said sites are inaccessible.

NOTES:

This backdoor then searches for files and folders in the removable drives then creates a copy of itself as {file or folder name}.exe.

It then sets the attribute of the original file or folder to Read-Only, Hidden and System and attempts to use the same icon to trick users that they are opening the legitimate file or folder.

  SOLUTION

Minimum Scan Engine:

9.300

FIRST VSAPI PATTERN FILE:

10.216.03

FIRST VSAPI PATTERN DATE:

14 Aug 2013

VSAPI OPR PATTERN File:

10.217.00

VSAPI OPR PATTERN Date:

15 Aug 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

Identify and terminate files detected as WORM_FLASHBOT.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 3

Delete this registry key

[ 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
    • syscheck

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.
  • %Windows%\Tasks\FlashDrv.job
  • %User Temp%\fdg{random}.tmp.exe

Step 5

Scan your computer with your Trend Micro product to delete files detected as WORM_FLASHBOT.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 this Knowledge Base page for more information.


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