WORM_SMALL.BIX

April 27, 2020
 Analysis by: Johnlery Triunfante
 ALIASES:

Worm.Win32.Small.i (Kaspersky); W32.Resik.A (Norton); Worm:Win32/Small (Microsoft)

 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:

Downloaded from the Internet, Dropped by other malware, Via physical/removable drives

This Worm arrives by connecting affected removable drives to a system. It arrives on a system as a file dropped by other malware or as a file downloaded unknowingly by users when visiting malicious sites.

It drops an AUTORUN.INF file to automatically execute the copies it drops when a user accesses the drives of an affected system.

  TECHNICAL DETAILS

File Size:

24,576 bytes

File Type:

EXE

Memory Resident:

Yes

Initial Samples Received Date:

15 Apr 2011

Payload:

Drops files

Arrival Details

This Worm arrives by connecting affected removable drives to a system.

It 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:

  • {Drive Letter}:\autorun.inf
  • {Drive Letter}:\Recycled\voinfo.dll
  • If %System%\Driveinfo.exe exists:
    • %System%\Driveinfo.log
    • {Drive Letter}:\Recycled\Driveinfo.sdc

(Note: %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:

  • %System%\inetsrv.exe

(Note: %System% is the Windows system folder, where it usually is C:\Windows\System32 on all Windows operating system versions.)

It adds the following processes:

  • "%System%\attrib.exe" +r +a +h +s "{Drive Letter}:\Recycled" /s /d
  • "%System%\attrib.exe" +r +a +h +s {Drive Letter}:\autorun.inf /s /d
  • "%System%\attrib.exe" +r +a +h +s "{Drive Letter}:\Recycled\*.*" /s /d
  • "%Windows%\explorer.exe" {Drive Letter}:

(Note: %System% is the Windows system folder, where it usually is C:\Windows\System32 on all Windows operating system versions.. %Windows% is the Windows folder, where it usually is C:\Windows on all Windows operating system versions.)

Autostart Technique

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

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\
Windows\CurrentVersion\Run
inetsrv = %System%\inetsrv.exe

Other System Modifications

This Worm adds the following registry entries:

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\
Windows\Help
VersionNumber = {value}

Propagation

This Worm creates the following folder in all physical and removable drives:

  • {Drive Letter}:\Recycled

It drops the following copy of itself in all physical and removable drives:

  • {Drive Letter}:\Recycled\Driveinfo.exe

It drops an AUTORUN.INF file to automatically execute the copies it drops when a user accesses the drives of an affected system.

The said .INF file contains the following strings:

[AutoRun]
Open=.\Recycled\Driveinfo.exe
Shell\Open\Command=.\Recycled\Driveinfo.exe

Other Details

This Worm does the following:

  • It terminates itself if it is not located in a folder named Recycled or system32 (case sensitive).

  SOLUTION

Minimum Scan Engine:

9.850

VSAPI OPR PATTERN File:

5.883.00

VSAPI OPR PATTERN Date:

08 Apr 2009

Step 1

Before doing any scans, Windows 7, Windows 8, Windows 8.1, and Windows 10 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

Restart in Safe Mode

[ Learn More ]

Step 4

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_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Run
    • inetsrv = %System%\inetsrv.exe
  • In HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\Help
    • VersionNumber = {value}

Step 5

Search and delete this folder

[ 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.
  • {Drive Letter}:\Recycled

Step 6

Search and delete AUTORUN.INF files created by WORM_SMALL.BIX that contain these strings

[ Learn More ]
  • [AutoRun]
  • Open=.\Recycled\Driveinfo.exe
  • Shell\Open\Command=.\Recycled\Driveinfo.exe

Step 7

Search and delete these files

[ 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.
  • %System%\Driveinfo.log
  • %System%\inetsrv.exe
  • {Drive Letter}:\Recycled\Driveinfo.sdc
  • {Drive Letter}:\Recycled\Driveinfo.exe

Step 8

Restart in normal mode and scan your computer with your Trend Micro product for files detected as WORM_SMALL.BIX. 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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