WORM_BSRAT.A

October 08, 2012
 Analysis by: jasperm
 ALIASES:

Symantec: W32.Shadesrat

 PLATFORM:

Windows 2000, XP, Server 2003

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

  • Threat Type: Worm

  • Destructiveness: No

  • Encrypted: Yes

  • In the wild: Yes

  OVERVIEW

This worm may be dropped by other malware. It may be unknowingly downloaded by a user while visiting malicious websites.

It connects to a website to send and receive information.

It also has rootkit capabilities, which enables it to hide its processes and files from the user.

  TECHNICAL DETAILS

File Size:

389,147 bytes

File Type:

PE

Memory Resident:

Yes

Initial Samples Received Date:

24 Feb 2011

Arrival Details

This worm may be dropped by other malware.

It may be unknowingly downloaded by a user while visiting malicious websites.

Installation

This worm drops the following files:

  • %Application Data%\data.dat - log file of its activities

(Note: %Application Data% is the current user's Application Data folder, which is usually C:\Windows\Profiles\{user name}\Application Data on Windows 98 and ME, C:\WINNT\Profiles\{user name}\Application Data on Windows NT, and C:\Documents and Settings\{user name}\Local Settings\Application Data on Windows 2000, XP, and Server 2003.)

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

  • %Appilcation Data%\csrss.exe

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
nvdisplay = %Application Data%\csrss.exe

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\
Active Setup\Installed Components\{4FD0ADA0-A658-AACB-BFBA-3DEA7BBDBA2D}
StubPath = %Application Data%\csrss.exe

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\
Windows\CurrentVersion\Run
nvdisplay = %Application Data%\csrss.exe

Other System Modifications

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

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

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\
Services\SharedAccess\Parameters\
FirewallPolicy\StandardProfile\AuthorizedApplications\
List
%Application Data%\csrss.exe = %Application Data%\csrss.exe:*:Enabled:Windows Messanger

Backdoor Routine

This worm connects to the following websites to send and receive information:

  • hokaboga.no-ip.org

Rootkit Capabilities

This worm also has rootkit capabilities, which enables it to hide its processes and files from the user.

  SOLUTION

Minimum Scan Engine:

8.900

VSAPI PATTERN File:

under testing

Step 1

For Windows XP and Windows Server 2003 users, before doing any scans, please make sure you disable System Restore to allow full scanning of your computer.

Step 2

Identify and delete files detected as WORM_BSRAT.A using either the Startup Disk or Recovery Console

[ Learn More ]

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.

 HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\policies\Explorer\run
  • nvdisplay = %Application Data%\csrss.exe
  • In HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Run
    • nvdisplay = %Application Data%\csrss.exe
  • In HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\SharedAccess\Parameters\FirewallPolicy\StandardProfile\AuthorizedApplications\List
    • %Application Data%\csrss.exe =%Application Data%\csrss.exe:*:Enabled:Windows Messanger

    • Step 4

    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\Software
      • VB and VBA Program Settings
    • In HKEY_CURRENT_USER\Software\Microsoft\Active Setup\Installed Components
      • {4FD0ADA0-A658-AACB-BFBA-3DEA7BBDBA2D}

    Step 5

    Search and delete this file

    [ Learn More ]
    There may be some component 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%\data.dat

    Step 6

    Scan your computer with your Trend Micro product to delete files detected as WORM_BSRAT.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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