Analysis by: Anthony Joe Melgarejo
ALIASES:

Trojan.Win64.Sofacy.i (Kaspersky)

 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: 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 commands from a remote malicious user, effectively compromising the affected system.

  TECHNICAL DETAILS

File Size: 95,744 bytes
File Type: DLL
Memory Resident: Yes
Initial Samples Received Date: 31 Oct 2014
Payload: Connects to URLs/IPs

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:

  • {dropped file path}\advstorshell.dll - detected as BKDR64_SEDNIT.A
  • %User Temp%\tmp.dat - contains systeminfo results
  • %User Temp%\__4964tmp.dat - contains encryption key
  • {dropped file path}\nttmp.dat - backup of advstorshell.dll if it is already existing in the {dropped file path}

(Note: %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 adds the following mutexes to ensure that only one of its copies runs at any one time:

  • DerNaTcMt

It terminates itself if it finds the following processes in the affected system's memory:

  • netsniffer.exe
  • windump.exe
  • winapioverride32.exe
  • tcpview.exe
  • vboxservice.exe
  • procexp.exe
  • wireshark.exe
  • regmon.exe
  • procmon.exe
  • iris.exe
  • petools.exe
  • filemon.exe
  • vboxtray.exe
  • tcpdump.exe
  • apimonitor.exe
  • odb.exe
  • apispy32.exe
  • comview.exe
  • winspy.exe
  • vmtools.exe
  • vmwaretray.exe
  • immunitydebugger.exe
  • syser.exe
  • dumpcap.exe
  • vmwareuser.exe
  • idag64.exe
  • ollydbg.exe
  • windbg.exe
  • idag.exe

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
AdvanceStorageShell = "RUNDLL32.EXE "{dropped file path}\advstorshell.dll,InitW""

Other System Modifications

This backdoor adds the following registry entries as part of its installation routine:

HKEY_CURRENT_USER\Software\Microsoft\
Windows\CurrentVersion\Explorer
Path = "{encrypted CnCs, computer name and OS version}"

HKEY_LOCAL_MACHINE\Software\Microsoft\
Windows\CurrentVersion\Explorer
Path = "{encrypted CnCs, computer name and OS version}"

HKEY_LOCAL_MACHINE\Software\Classes\
CLSID\{2D876AE9-4412-7513-29A6-9436AE031980}\InProcServer32
Default = "{dropped file path}\advstorshell.dll"

HKEY_LOCAL_MACHINE\Software\Classes\
CLSID\{2D876AE9-4412-7513-29A6-9436AE031980}\InProcServer32
Threading Model = Apartment

It adds the following registry keys as part of its installation routine:

HKEY_LOCAL_MACHINE\Software\Classes\
CLSID\{2D876AE9-4412-7513-29A6-9436AE031980}\InProcServer32

Backdoor Routine

This backdoor executes the following commands from a remote malicious user:

  • Downloads and execute arbitrary files

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

  • http://{BLOCKED}rvice24.net/update
  • http://[BLOCKED}oftware24.com/update
  • http://{BLOCKED}pc.org/update

It posts the following information to its command and control (C&C) server:

  • Computer name
  • OS version
  • Running processes
  • System information (result of systeminfo command)
  • Drive(s) information
  • Keylog
  • Registry information

NOTES:

The {dropped file path} can be any of the following:

  • %AppDataLocal%\Microsoft Help
  • %Program Files%\Common\Microsoft Shared\MSInfo

  SOLUTION

Minimum Scan Engine: 9.700

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

Scan your computer with your Trend Micro product to delete files detected as BKDR64_SEDNIT.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.

Step 4

Search and delete these files

[ 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.
  • %User Temp%\tmp.dat
  • %User Temp%\__4964tmp.dat

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
    • AdvanceStorageShell = "RUNDLL32.EXE "{dropped file path}\advstorshell.dll,InitW""
  • In HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Explorer
    • Path = "{encrypted CnCs, computer name and OS version}"
  • In HKEY_LOCAL_MACHINE\Software\Microsoft\Windows\CurrentVersion\Explorer
    • Path = "{encrypted CnCs, computer name and OS version}"

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. Before you could do this, you must restart in Safe Mode. For instructions on how to do this, you may refer to this page If the preceding step requires you to restart in safe mode, you may proceed to edit the system registry.

  • In HKEY_LOCAL_MACHINE\Software\Classes\CLSID
    • {2D876AE9-4412-7513-29A6-9436AE031980}

Step 7

Restart in normal mode and scan your computer with your Trend Micro product for files detected as BKDR64_SEDNIT.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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