Analysis by: Maria Emreen Viray

ALIASES:

Backdoor.PHP.WebShell.gd (KASPERSKY)

 PLATFORM:

Windows, Linux

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

  • Threat Type: Backdoor

  • Destructiveness: No

  • Encrypted:

  • In the wild: Yes

  OVERVIEW

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 does not have any propagation routine.

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

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

  TECHNICAL DETAILS

Tamaño del archivo 159,795 bytes
Tipo de archivo PHP
Residente en memoria No
Fecha de recepción de las muestras iniciales 27 Oct 2020

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.

Propagation

This Backdoor does not have any propagation routine.

Backdoor Routine

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

  • Execute arbitrary commands
  • Execute specific command line commands
  • Execute port scanning
  • Download files from specified URL
  • Steal information specified in gathered data
  • Execute SQL commands
  • Create reverse shell
  • Download files through FTP
  • Brute force database credentials
  • Add user accounts
  • Inject code into specific files
  • XOR encode strings
  • Manage files (create directory, create files, delete, query)
  • Manage registry entries (create, delete)
  • Upload/download files

Rootkit Capabilities

This Backdoor does not have rootkit capabilities.

Information Theft

This Backdoor gathers the following data:

  • Server Time Started
  • Server domain name
  • Server IP Address
  • Server OS text encoding
  • Server Engine
  • IP Address of infected machine
  • Web Service Port
  • File Path
  • Server Admin
  • Disk free space
  • Existence of/Ability to do the following in the server:
    • Allow file to be opened using URL
    • Allows dynamic loading of linked libraries
    • Display error message
    • Automatically define register_globals in global variables
    • magic_quotes_gpc
    • max memory allowed by program
    • memory_limit POST max bytes
    • max allowed upload file size
    • max running time of program
    • phpinfo() function
    • Graphics processing GD Library
    • IMAP email system
    • MySQL database
    • SyBase database
    • Oracle database
    • Oracle 8 database
    • PREL compatible syntax PCRE
    • PDF document support
    • Postgre SQL database SNMP
    • Network Management protocol
    • Zlib/Compressed file support
    • xML analysis
    • FTP
    • ODBC database connection
    • Session support
    • Socket Support

Other Details

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

It requires being hosted on a web server in order to proceed with its intended routine.

NOTES:

This Backdoor does the following:

  • It requires the following password to be accessed by users:
    • YGHFK
  • It uses the following URLs and files as placeholders in the given backdoor commands:
    • for URL used in Code injection:
      • http://{BLOCKED}bap.org/ad.js?{6 Random Characters}
    • for Download files from specified URL:
      • http://{BLOCKED}bap.org/a.exe (saves file as {Directory pointed by __FILE__ PHP environment variable}\a.exe)
    • for FTP server used in Download files through FTP:
      • {BLOCKED}.{BLOCKED}.222.1 (saves file as C:\silic.exe)
    • for string used for XOR encode strings:
      • http://{BLOCKED}bap.org/hello.exe

  SOLUTION

Motor de exploración mínimo 9.800
Primer archivo de patrones de VSAPI 17.240.04
Primera fecha de publicación de patrones de VSAPI 08 Dec 2021
Versión de patrones OPR de VSAPI 17.241.00
Fecha de publicación de patrones OPR de VSAPI 09 Dec 2021

Step 1

Before doing any scans, Windows 7, Windows 8, Windows 8.1, and Windows 10 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

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.  
  • {Directory pointed by __FILE__ PHP environment variable}\a.exe
  • C:\silic.exe

Step 4

Scan your computer with your Trend Micro product to delete files detected as Backdoor.PHP.WEBSHELL.SBGIFLD. 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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