BKDR_GRAVITYRAT.A

April 30, 2018
 Analysis by: Patrick Angelo Roderno
 ALIASES:

Backdoor.MSIL.Agent.zmx (KASPERSKY); W32.Golroted (NORTON); Gen:Heur.Bodegun.1 (BITDEFENDER)

 PLATFORM:

Windows

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

  • Threat Type: Backdoor

  • Destructiveness: No

  • Encrypted: No

  • In the wild: Yes

  OVERVIEW

Infection Channel:

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 connects to a website to send and receive information.

  TECHNICAL DETAILS

File Size:

933,376 bytes

File Type:

EXE

Memory Resident:

No

Initial Samples Received Date:

22 Dec 2016

Payload:

Connects to URLs/IPs, Drops files, Steals information

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 creates the following folders:

  • %AppDataLocal%\Microsoft\Sys_Files
  • %AppDataLocal%\Microsoft\002\003

(Note: %AppDataLocal% is the Application Data folder found in Local Settings, where it is usually C:\Documents and Settings\{user name}\Local Settings\Application Data on Windows 2000, Windows Server 2003, and Windows XP (32- and 64-bit); C:\Users\{user name}\AppData\Local 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.)

Backdoor Routine

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

  • http://{BLOCKED}date.{BLOCKED}pdates.com:46769/Gvty@/1ns3rt_39291384.php
  • http://{BLOCKED}tes.{BLOCKED}soft.com:46769/Gvty@/1ns3rt_39291384.php
  • http://{BLOCKED}server.{BLOCKED}pdates.eu:46769/Gvty@/1ns3rt_39291384.php

Dropping Routine

This Backdoor drops the following files:

  • %AppDataLocal%\Microsoft\Sys_Files\c#$k.txt - infection marker of the backdoor

(Note: %AppDataLocal% is the Application Data folder found in Local Settings, where it is usually C:\Documents and Settings\{user name}\Local Settings\Application Data on Windows 2000, Windows Server 2003, and Windows XP (32- and 64-bit); C:\Users\{user name}\AppData\Local 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 drops the following file, into which it saves gathered information:

  • %AppDataLocal%\Microsoft\Sys_Files\$K&n.txt - contains the names of all files with specific extensions in the affected system
  • %AppDataLocal%\Microsoft\Sys_Files\fupld.txt - files uploaded to the C&C server
  • %AppDataLocal%\Microsoft\Sys_Files\ftoup.txt - files to be uploaded to the C&C server
  • %AppDataLocal%\Microsoft\Sys_Files\fupva.txt - number of uploaded files

(Note: %AppDataLocal% is the Application Data folder found in Local Settings, where it is usually C:\Documents and Settings\{user name}\Local Settings\Application Data on Windows 2000, Windows Server 2003, and Windows XP (32- and 64-bit); C:\Users\{user name}\AppData\Local 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.)

Download Routine

This Backdoor saves the files it downloads using the following names:

  • %AppDataLocal%\Microsoft\002\003\{Payload Name}

(Note: %AppDataLocal% is the Application Data folder found in Local Settings, where it is usually C:\Documents and Settings\{user name}\Local Settings\Application Data on Windows 2000, Windows Server 2003, and Windows XP (32- and 64-bit); C:\Users\{user name}\AppData\Local 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.)

Information Theft

This Backdoor gathers the following data:

  • MAC Address
  • PC Name
  • Username
  • IP Address
  • Current Date
  • Files with the following extensions in all fixed drives:
    • .docx
    • .doc
    • .pptx
    • .ppt
    • .xlsx
    • .xls
    • .rtf
    • .pdf

Other Details

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

  • http://{BLOCKED}.{BLOCKED}.153.99:46769/Gvty@/ip.php

  SOLUTION

Minimum Scan Engine:

9.850

FIRST VSAPI PATTERN FILE:

14.216.06

FIRST VSAPI PATTERN DATE:

27 Apr 2018

VSAPI OPR PATTERN File:

14.217.00

VSAPI OPR PATTERN Date:

28 Apr 2018

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

Identify and terminate files detected as BKDR_GRAVITYRAT.A

[ Learn More ]
  1. Windows Task Manager may not display all running processes. In this case, please use a third-party process viewer, preferably Process Explorer, to terminate the malware/grayware/spyware file. You may download the said tool here.
  2. If the detected file is displayed in either Windows Task Manager or Process Explorer but you cannot delete it, restart your computer in safe mode. To do this, refer to this link for the complete steps.
  3. If the detected file is not displayed in either Windows Task Manager or Process Explorer, continue doing the next steps.

Step 4

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.  
  • %AppDataLocal%\Microsoft\Sys_Files
  • %AppDataLocal%\Microsoft\002

Step 5

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