WORM_SLENFBOT.XN

 Analysis by: Alvin Bacani

 ALIASES:

W32/Slenfbot.AE!tr (Fortinet)

 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: Yes

  • In the wild: Yes

  OVERVIEW

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 bypasses the Windows firewall. This allows the malware to perform its intended routine without being detected by an installed firewall.

  TECHNICAL DETAILS

File Size:

259,584 bytes

File Type:

EXE

Memory Resident:

Yes

Initial Samples Received Date:

14 May 2012

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:

  • %system%\wmpdt86.exe

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
Windows Data Recovery = "%system%\wmpdt86.exe"

Other System Modifications

This worm modifies the following registry entries to disable the Windows Firewall settings:

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\
Services\SharedAccess\Parameters\
FirewallPolicy\DomainProfile\AuthorizedApplications\
List
%system%\wmpdt86.exe = "%system%\wmpdt86.exe:*:Enabled:Windows Data Recovery"

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\
Services\SharedAccess\Parameters\
FirewallPolicy\StandardProfile\AuthorizedApplications\
List
%system%\wmpdt86.exe = "%system%\wmpdt86.exe:*:Enabled:Windows Data Recovery"

Other Details

This worm connects to the following possibly malicious URL:

  • http://{BLOCKED}.{BLOCKED}.53.179/ip/0x2f.txt
  • http://{BLOCKED}.{BLOCKED}.237.50/aspnet_client/ip/0x2f.txt
  • http://{BLOCKED}.{BLOCKED}.213.67/awstats/rdat02.txt

  SOLUTION

Minimum Scan Engine:

9.300

FIRST VSAPI PATTERN FILE:

9.103.01

FIRST VSAPI PATTERN DATE:

14 May 2012

VSAPI OPR PATTERN File:

9.104.00

VSAPI OPR PATTERN Date:

14 May 2012

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

Terminate a malware/grayware process

[ Learn More ]

*Note: If the detected process is not displayed in theWindows Task Manager, continue doing the next steps.

     
    • %system%\wmpdt86.exe

Step 3

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.
  • %system%\wmpdt86.exe

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
    • Windows Data Recovery = "%system%\wmpdt86.exe"
  • In HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\SharedAccess\Parameters\FirewallPolicy\DomainProfile\AuthorizedApplications\List
    • %system%\wmpdt86.exe = "%system%\wmpdt86.exe:*:Enabled:Windows Data Recovery"
  • In HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\SharedAccess\Parameters\FirewallPolicy\StandardProfile\AuthorizedApplications\List
    • %system%\wmpdt86.exe = "%system%\wmpdt86.exe:*:Enabled:Windows Data Recovery"

Step 5

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