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BKDR_NECURS.XXTV

March 08, 2015
 Modified by: Jaime Benigno Reyes
 ALIASES:

Trojan-Dropper.Win32.Necurs.xje (Kaspersky)

 PLATFORM:

Windows

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

  • Threat Type: Backdoor

  • Destructiveness: No

  • Encrypted: Yes

  • In the wild: Yes

  OVERVIEW


This backdoor is injected into all running processes to remain memory resident.

It modifies registry entries to disable the Windows Firewall settings. This action allows this malware to perform its routines without being deteted by the Windows Firewall.

It runs certain commands that it receives remotely from a malicious user. Doing this puts the affected computer and information found on the computer at greater risk. However, as of this writing, the said sites are inaccessible.

It creates an event. It deletes the initially executed copy of itself.

  TECHNICAL DETAILS

File Size:

84,992 bytes

File Type:

EXE

Memory Resident:

Yes

Initial Samples Received Date:

25 Feb 2015

Payload:

Connects to URLs/IPs, Compromises system security

Installation

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

  • %Windows%\Installer\{GUID}\syshost.exe - if logged in as an Administrator
  • %Application Data%\{GUID}\syshost.exe - if not logged in as an Administrator
  • %User Temp%\{random}.tmp

(Note: %Windows% is the Windows folder, where it usually is C:\Windows on all Windows operating system versions.. %Application Data% is the Application Data folder, where it usually is C:\Documents and Settings\{user name}\Application Data on Windows 2000, Windows Server 2003, and Windows XP (32- and 64-bit); C:\Users\{user name}\AppData\Roaming on Windows Vista (32- and 64-bit), Windows 7 (32- and 64-bit), Windows 8 (32- and 64-bit), Windows 8.1 (32- and 64-bit), Windows Server 2008, and Windows Server 2012.. %User Temp% is the user's temporary folder, where it usually is C:\Documents and Settings\{user name}\Local Settings\Temp on Windows 2000, Windows Server 2003, and Windows XP (32- and 64-bit); C:\Users\{user name}\AppData\Local\Temp on Windows Vista (32- and 64-bit), Windows 7 (32- and 64-bit), Windows 8 (32- and 64-bit), Windows 8.1 (32- and 64-bit), Windows Server 2008, and Windows Server 2012.)

It creates the following folders:

  • %Windows%\Installer\{GUID} - if logged in as an Administrator
  • %Application Data%\{GUID} - if not logged in as an Administrator

(Note: %Windows% is the Windows folder, where it usually is C:\Windows on all Windows operating system versions.. %Application Data% is the Application Data folder, where it usually is C:\Documents and Settings\{user name}\Application Data on Windows 2000, Windows Server 2003, and Windows XP (32- and 64-bit); C:\Users\{user name}\AppData\Roaming on Windows Vista (32- and 64-bit), Windows 7 (32- and 64-bit), Windows 8 (32- and 64-bit), Windows 8.1 (32- and 64-bit), Windows Server 2008, and Windows Server 2012.)

It is injected into all running processes to remain memory resident.

Autostart Technique

This backdoor registers itself as a system service to ensure its automatic execution at every system startup by adding the following registry entries:

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\
Services\syshost32
ImagePath = ImagePath = ""%Windows%\Installer\{GUID}\syshost.exe" /service"

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

HKEY_CURRENT_USER\Software\Microsoft\
Windows\CurrentVersion\Run
syshost32 = "%Windows%\Installer\{GUID}\syshost.exe"

It registers as a system service to ensure its automatic execution at every system startup by adding the following registry keys:

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\
Services\syshost32

Other System Modifications

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

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

(Note: The default value data of the said registry entry is "1".)

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

(Note: The default value data of the said registry entry is "1".)

Backdoor Routine

This backdoor executes the following command(s) from a remote malicious user:

  • download and execute arbitrary file

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

  • http://{BLOCKED}.{BLOCKED}.208.161/docs/index.php

However, as of this writing, the said sites are inaccessible.

Other Details

This backdoor connects to the following URL(s) to check for an Internet connection:

  • Facebook.com
  • Microsoft.com

It connects to the following URL(s) to get the affected system's IP address:

  • http://checkip.dyndns.org
  • http://ipv4.icanhazip.com

It does the following:

  • It performs a netsh.exe command that disables Windows Firewall depending on the OS version.
  • It elevates certain privileges when not in Administrator mode.

It creates the following event(s):

  • Global\NitrGB
  • Local\NitrGB

It deletes the initially executed copy of itself

  SOLUTION

Minimum Scan Engine:

9.750

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

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

Scan your computer with your Trend Micro product and note files detected as BKDR_NECURS.XXTV

Step 4

Restart in Safe Mode

[ Learn More ]

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
    • syshost32 = "%Windows%\Installer\{GUID}\syshost.exe"

Step 6

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\Services
    • syshost32

Step 7

Restore this modified 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\SYSTEM\CurrentControlSet\Services\SharedAccess\Parameters\FirewallPolicy\DomainProfile
    • From: DoNotAllowExceptions = "0"
      To: DoNotAllowExceptions = "1"
  • In HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\SharedAccess\Parameters\FirewallPolicy\StandardProfile
    • From: DoNotAllowExceptions = "0"
      To: DoNotAllowExceptions = "1"

Step 8

Search and delete these folders

[ 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%\Installer\{GUID} - if logged in as an Administrator
  • %Application Data%\{GUID} - if not logged in as an Administrator

Step 9

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