ALIASES:

RDN/Downloader.a!gc (McAfee); Backdoor.Win32.Nuclear.as (Kaspersky); Backdoor.Nuclear.dg (fs) (Sunbelt); May be infected by unknown virus Win32/DH{MR4DCQgUTxUbCg} (AVG)

 PLATFORM:

Windows 2000, Windows XP, Windows Server 2003

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

  • Threat Type: Backdoor

  • Destructiveness: No

  • Encrypted:

  • In the wild: Yes

  OVERVIEW

This backdoor arrives on a system as a file dropped by other malware or as a file downloaded unknowingly by users when visiting malicious sites.

It deletes itself after execution.

  TECHNICAL DETAILS

File Size: 331,387 bytes
File Type: EXE
Memory Resident: Yes
Initial Samples Received Date: 04 Jun 2013

Arrival Details

This backdoor 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 backdoor drops the following copies of itself into the affected system:

  • %Windows%\WINDOWS\installC.exe

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

It creates the following folders:

  • %Windows%\WINDOWS

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

Autostart Technique

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

HKEY_CURRENT_USER\Software\Microsoft\
Windows\CurrentVersion\Run
installC = "%Windows%\WINDOWS\installC.exe"

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\
Windows\CurrentVersion\Run
installC = "%Windows%\WINDOWS\installC.exe"

Other System Modifications

This backdoor deletes the following files:

  • %Windows%\WINDOWS\installC.exe

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

It adds the following registry keys:

HKEY_CLASSES_ROOT\dllfile\shell\
open\command

It adds the following registry entries:

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\
Active Setup
SOFTWARE\Microsoft\Active Setup = "StubPath"

It deletes the following registry keys:

HKEY_CURRENT_USER\SOFTWARE\Microsoft\
Active Setup

Dropping Routine

This backdoor drops the following files:

  • %Windows%\WINDOWS\installC.sys
  • %User Temp%\_ssf.vbs
  • %User Startup%\installC.lnk

(Note: %Windows% is the Windows folder, which is usually C:\Windows.. %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.. %User Startup% is the current user's Startup folder, which is usually C:\Windows\Profiles\{user name}\Start Menu\Programs\Startup on Windows 98 and ME, C:\WINNT\Profiles\{user name}\Start Menu\Programs\Startup on Windows NT, and C:\Documents and Settings\{User name}\Start Menu\Programs\Startup.)

Other Details

This backdoor deletes itself after execution.

This report is generated via an automated analysis system.

  SOLUTION

Minimum Scan Engine: 9.300

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_CLASSES_ROOT\dllfile\shell\open
    • command

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_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Run
    • installC = "%Windows%\WINDOWS\installC.exe"
  • In HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Run
    • installC = "%Windows%\WINDOWS\installC.exe"
  • In HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Active Setup
    • SOFTWARE\Microsoft\Active Setup = "StubPath"

Step 5

Search and delete these components

[ Learn More ]
There may be some components 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%\WINDOWS\installC.sys
  • %User Temp%\_ssf.vbs
  • %User Startup%\installC.lnk

Step 6

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.
  • %Windows%\WINDOWS

Step 7

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

Step 8

Restore this file from backup only Microsoft-related files will be restored. If this malware/grayware also deleted files related to programs that are not from Microsoft, please reinstall those programs on you computer again.

  • %Windows%\WINDOWS\installC.exe

Step 9

Restore these deleted registry keys/values from backup

*Note: Only Microsoft-related keys/values will be restored. If the malware/grayware also deleted registry keys/values related to programs that are not from Microsoft, please reinstall those programs on your computer.

  • In HKEY_CURRENT_USER\SOFTWARE\Microsoft
    • Active Setup


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