Author: Noel Anthony Llimos   

 

HEUR:Backdoor.Linux.Vpnfilter.a (Kaspersky), Trojan:Linux/VPNFilt (Microsoft)

 PLATFORM:

Linux

 OVER ALL RISK RATING:
 DAMAGE POTENTIAL:
 DISTRIBUTION POTENTIAL:
 REPORTED INFECTION:
 INFORMATION EXPOSURE
Low
Medium
High
Critical

  • Threat Type:
    Trojan

  • Destructiveness:
    No

  • Encrypted:
     

  • In the wild:
    Yes

  OVERVIEW

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

As of this writing, the said sites are inaccessible.

  TECHNICAL DETAILS

File size: 493,448 bytes
File type: ELF
Memory resident: Yes
INITIAL SAMPLES RECEIVED DATE: 25 May 2018

Arrival Details

This Trojan 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 Trojan drops the following files:

  • /var/run/client.crt <--- Used to authenticate request to the C&C Server
  • /var/run/client.key <--- Used to authenticate request to the C&C Server
  • /var/run/client_ca.crt <--- Used to authenticate request to the C&C Server

Download Routine

This Trojan connects to the following URL(s) to download its configuration file:

  • http://photobucket.com/user/katy{BLOCKED}45/library
  • http://photobucket.com/user/lisa{BLOCKED}87/library
  • http://photobucket.com/user/kmi{BLOCKED}2/library
  • http://photobucket.com/user/nik{BLOCKED}d11/library

As of this writing, the said sites are inaccessible.

Other Details

This Trojan does the following:

  • It modifies Cron/Crontab (Linux Script Scheduler) to execute a script periodically. It schedules it to run every 5 minutes.
  • It is capable of downloading different modules from the C&C Server.
  • If it fails to connect to the initial URL, it then proceeds to connect to the following backup URL for the second payload:
    • http://{BLOCKED}wall.com/manage/content/update.php
  • If it fails to connect to the URL, it opens a port that waits for a specific trigger to establish a connection for the author to have access interactively to the infected device.
  • It generates a URL from the configuration file where it will download and save the file using the following names
    • /var/vpnfilter

  SOLUTION

Minimum scan engine: 9.850
First VSAPI Pattern File: 14.274.04
First VSAPI Pattern Release Date: 24 May 2018
VSAPI OPR PATTERN-VERSION: 14.275.00
VSAPI OPR PATTERN DATE: 25 May 2018

Scan your computer with your Trend Micro product to delete files detected as ELF_VPNFILT.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 the following Trend Micro Support pages for more information:


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