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BKDR_ZEGOST.YNSK

February 04, 2016
 Analysis by: Rhena Inocencio
 ALIASES:

Backdoor:Win32/Zegost!rfn (Microsoft), a variant of Win32/Farfli.OC (ESET)

 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

Infection Channel:

Downloaded from the Internet

This backdoor may be unknowingly downloaded by a user while visiting malicious websites.

It executes commands from a remote malicious user, effectively compromising the affected system. It connects to a website to send and receive information.

It logs a user's keystrokes to steal information.

However, as of this writing, the said sites are inaccessible. It deletes the initially executed copy of itself. It gathers information and reports it to its servers.

  TECHNICAL DETAILS

File Size:

184,712 bytes

File Type:

EXE

Memory Resident:

Yes

Payload:

Connects to URLs/IPs, Steals information, Terminates processes

Arrival Details

This backdoor may be unknowingly downloaded by a user while visiting malicious websites.

Installation

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

  • %Windows%\1005C8E6\svchsot.exe

(Note: %Windows% is the Windows folder, where it usually is C:\Windows on all Windows operating system versions.)

It drops the following component file(s):

  • %Windows%\Task\At{number}.job - scheduled task

(Note: %Windows% is the Windows folder, where it usually is C:\Windows on all Windows operating system versions.)

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

  • abcstudy.f3322.net:23668abcstudy.f3322.net:23668abcstudy.f3322.net:23668

Autostart Technique

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

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\
Windows\CurrentVersion\Run
1005C8E6 = "%Windows%\1005C8E6\svchsot.exe"

The scheduled task executes the malware every:

  • 1 hour (everyday)

Backdoor Routine

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

  • Download files
  • Perform remote shell command
  • Capture screenshots
  • Perform DDOS attack

It connects to the following websites to send and receive information:

  • abcstudy.f3322.net

Process Termination

This backdoor terminates the following processes if found running in the affected system's memory:

  • avp.exe
  • KSafeTray.exe
  • Rstray.exe
  • 360tray.exe
  • RavMonD.exe
  • QQPCTray.exe
  • KvMonXP.exe
  • egui.exe
  • kxetray.exe

Download Routine

This backdoor accesses the following websites to download files:

  • http://abcstudy.{BLOCKED}2.net:2011/1.exe

Information Theft

This backdoor logs a user's keystrokes to steal information.

Other Details

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

It deletes the initially executed copy of itself

It gathers the following information and reports it to its servers:

  • Processor Speed
  • ComputerName
  • OS Version
  • Drive Information

NOTES:

This malware requires the following files to perform its distributed denial of service (DDoS) attack:

  • {malware path}\DNM.ini
  • {malware path}\DN.ini
  • {malware path}\UDM.ini
  • {malware path}\UD.ini
  • {malware path}\SYM.ini
  • {malware path}\SY.ini
  • {malware path}\SPM.ini
  • {malware path}\SP.ini
  • {malware path}\ICM.ini
  • {malware path}\IC.ini

It executes the following normal processes to add the scheduled tasks:

  • net1.exe
  • net.exe

  SOLUTION

Minimum Scan Engine:

9.800

FIRST VSAPI PATTERN FILE:

12.260.03

FIRST VSAPI PATTERN DATE:

08 Jan 2016

VSAPI OPR PATTERN File:

12.261.00

VSAPI OPR PATTERN Date:

09 Jan 2016

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

Restart in Safe Mode

[ Learn More ]

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
    • 1005C8E6 = "%Windows%\1005C8E6\svchsot.exe"

Step 5

Search and delete these files

[ 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.
  • %Windows%\Task\At{number}.job

Step 6

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