BKDR_NECURS.AC

April 09, 2013
 Analysis by: Adrianne Chester Camat
 ALIASES:

Trojan:Win32/Necurs (Microsoft)

 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:

  • Threat Type: Backdoor

  • Destructiveness: No

  • Encrypted: Yes

  • In the wild: Yes

  OVERVIEW

Infection Channel:

Downloaded from the Internet, Dropped by other malware

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 executes then deletes itself afterward.

It connects to a website to send and receive information. However, as of this writing, the said sites are inaccessible.

It connects to certain URLs. It may do this to remotely inform a malicious user of its installation. It may also do this to download possibly malicious files onto the computer, which puts the computer at a greater risk of infection by other threats.

It creates an event.

  TECHNICAL DETAILS

File Size:

262,144 bytes

File Type:

EXE

Memory Resident:

Yes

Initial Samples Received Date:

08 Apr 2013

Payload:

Connects to URLs/IPs, Drops files

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 files:

  • %System%\drivers\{random}.sys - detected as RTKT_NECURS.AC

(Note: %System% is the Windows system folder, which is usually C:\Windows\System32.)

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

  • %Windows%\Installer\{Random GUID}\syshost.exe

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

It creates the following folders:

  • %Windows%\Installer\{Random GUID}

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

It executes then deletes itself afterward.

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 = ""%Windows%\Installer\{Random GUID}\syshost.exe" /service"

It creates the following registry entries to enable automatic execution of dropped component at every system startup:

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\
Windows\CurrentVersion\Run
syshost32 = %Windows%\Installer\{Random 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

It registers its dropped component as a system service to ensure its automatic execution at every system startup. It does this by creating the following registry entries:

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\
Services\{random}

Backdoor Routine

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

  • {BLOCKED}.ntp.org
  • {BLOCKED}.ntp.org

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

Download Routine

This backdoor connects to the following malicious URLs:

  • http://{BLOCKED}touls.tv/cgi-bin/meta.cgi
  • http://{BLOCKED}iwse.eu/cgi-bin/meta.cgi
  • http://{BLOCKED}valetoday.ws/cgi-bin/meta.cgi
  • http://{BLOCKED}.229.126/cgi-bin/meta.cgi
  • http://{BLOCKED}.229.131/cgi-bin/meta.cgi
  • http://{BLOCKED}.229.134/cgi-bin/meta.cgi

Other Details

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

  • facebook.com
  • microsoft.com

It creates the following event(s):

  • Global\NitrGB
  • Local\NitrGB

NOTES:
This backdoor elevates certain privileges when not in administrator mode.

It tries to delete the following Alternate Data Stream:

  • %System%\Installer\{Random GUID}\syshost.exe:Zone.Identifier

It hooks to the following System Service Descriptor Table (SSDT):

  • NtOpenThread
  • NtOpenProcess

  SOLUTION

Minimum Scan Engine:

9.300

FIRST VSAPI PATTERN FILE:

9.844.05

FIRST VSAPI PATTERN DATE:

08 Apr 2013

VSAPI OPR PATTERN File:

9.845.00

VSAPI OPR PATTERN Date:

08 Apr 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

Remove malware/grayware files dropped/downloaded by BKDR_NECURS.AC

     RTKT_NECURS.AC

Step 3

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

Step 4

Restart in Safe Mode

[ Learn More ]

Step 5

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
  • In HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services
    • {random}

Step 6

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

Step 7

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\{Random GUID}

Step 8

Restart in normal mode and scan your computer with your Trend Micro product for files detected as BKDR_NECURS.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 9

Scan your computer with your Trend Micro product to delete files detected as BKDR_NECURS.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 10

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. DATA_GENERIC
  • In the Look In drop-down list, select My Computer then press Enter.
  • Once located, select the file then press SHIFT+DELETE to delete it.

    • • For Windows Vista and Windows 7 users:

    1. Click Start>Computer.
    2. In the Search input box, type the following:
      DATA_GENERIC
    3. Once located, select the file then press SHIFT+DELETE to delete it.
      *Note: Read the following Microsoft page if these steps do not work on Windows 7.


    Did this description help? Tell us how we did.