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WORM_AINSLOT.FX

July 18, 2013
 Analysis by: Alvin Bacani
 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:
 REPORTED INFECTION:
 SYSTEM IMPACT RATING:
 INFORMATION EXPOSURE:

  • Threat Type: Worm

  • Destructiveness: No

  • Encrypted: Yes

  • 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.

It drops copies of itself into all the removable drives connected to an affected system.

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

It logs a user's keystrokes to steal information.

  TECHNICAL DETAILS

File Size:

2,326,528 bytes

File Type:

EXE

Memory Resident:

Yes

Initial Samples Received Date:

11 Jul 2013

Payload:

Steals information, 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%\Microsoft\winlogon.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:

  • %User Temp%\{random filename}.exe
  • %User Temp%\{random filename}.bat

(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.)

Autostart Technique

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

HKEY_CURRENT_USER\Software\Microsoft\
Windows\CurrentVersion\Run
Microsoft Winlogon = "%Application Data%\Microsoft\winlogon.exe"

Other System Modifications

This worm adds the following registry keys:

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\
Control\MediaResources
msvideo =

It adds the following registry entries as part of its installation routine:

HKEY_CURRENT_USER\Software\VB and VBA Program Settings\
INSTALL\DATE
{Random Value} = {Date of Execution}

HKEY_CURRENT_USER\Software\VB and VBA Program Settings\
SrvID\ID
{Random Value} = {Random}

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\
Services\SharedAccess\Parameters\
FirewallPolicy\StandardProfile
DoNotAllowExceptions = "0"

It creates the following registry entry(ies) to bypass Windows Firewall:

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\
Services\SharedAccess\Parameters\
FirewallPolicy\StandardProfile\AuthorizedApplications\
List
%Program Files%\Internet Explorer\iexplore.exe = "%Program Files%\Internet Explorer\iexplore.exe:*:Enabled:Windows Messanger"

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\
Services\SharedAccess\Parameters\
FirewallPolicy\StandardProfile\AuthorizedApplications\
List
%User Temp%\{random filename}.exe = "%User Temp%\{random filename}.exe:*:Enabled:Windows Messanger""

Propagation

This worm drops copies of itself into all the removable drives connected to an affected system.

Backdoor Routine

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

  • Download and execute files
  • Upload stolen information
  • Upload captured screen
  • Update copy of itself

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

  • api.{BLOCKED}db.com

Information Theft

This worm logs a user's keystrokes to steal information.

NOTES:
This worm may also take a screen shot of the affected system.

  SOLUTION

Minimum Scan Engine:

9.300

FIRST VSAPI PATTERN FILE:

10.150.01

FIRST VSAPI PATTERN DATE:

11 Jul 2013

VSAPI OPR PATTERN File:

10.151.00

VSAPI OPR PATTERN Date:

11 Jul 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

Restart in Safe Mode

[ Learn More ]

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_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\MediaResources
    • msvideo

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.  
  • %Application Data%\Microsoft\winlogon.exe
  • %User Temp%\{random filename}.exe
  • %User Temp%\{random filename}.bat

Step 5

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
    • Microsoft Winlogon = "%Application Data%\Microsoft\winlogon.exe"
  • In HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\SharedAccess\Parameters\FirewallPolicy\StandardProfile
    • DoNotAllowExceptions = "0"
  • In HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\SharedAccess\Parameters\FirewallPolicy\StandardProfile\AuthorizedApplications\List
    • %User Temp%\{random filename}.exe    %User Temp%\{random filename}.exe:*:Enabled:Windows Messanger
  • In HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\SharedAccess\Parameters\FirewallPolicy\StandardProfile\AuthorizedApplications\List
    • %Program Files%\Internet Explorer\iexplore.exe    %Program Files%\Internet Explorer\iexplore.exe:*:Enabled:Windows Messanger

Step 6

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