Ensiko is a PHP web shell with ransomware capabilities that targets various platforms such as Linux, Windows, macOS, or any other platform that has PHP installed. The malware has the capability to remotely control the system and accept commands to perform malicious activities on the infected machine.

It can also execute shell commands on an infected system and send the results back to the attacker via a PHP reverse shell. It is capable of scanning servers for the presence of other webshells, defacing websites, sending mass emails, downloading remote files, disclosing information about the affected server, brute-force attacks against file transfer protocol (FTP), cPanel, and Telnet, overwriting files with specified extensions, and more.

Technical Details

Webshell Authentication

The malware has the ability to be password-protected. For authentication, the malware displays a Not Found page with a hidden login form as seen in the next two figures:

 

 

 

The password for this sample is “RaBiitch”, while the following figure shows captured network traffic for an authentication request to the web shell panel:

Webshell features

The following is a list of Ensiko’s capabilities:

Features	Description
Priv Index	Download ensikology.php from pastebin
Ransomeware	Encrypt files using RIJNDAEL 128 with CBC mode
CGI Telnet	Download CGI-telnet version 1.3 from pastebin; CGI-Telnet is a CGI script that allows you to execute commands on your web server.
Reverse Shell	PHP Reverse shell
Mini Shell 2	Drop Mini Shell 2 webshell payload in ./tools_ensikology/
IndoXploit	Drop IndoXploit webshell payload in ./tools_ensikology/
Sound Cloud	Display sound cloud
Realtime DDOS Map	Fortinet DDoS map
Encode/Decode	Encode/decode string buffer
Safe Mode Fucker	Disable PHP Safe Mode
Dir Listing Forbidden	Turn off directory indexes
Mass Mailer	Mail Bombing
cPanel Crack	Brute-force cPanel, ftp, and telnet
Backdoor Scan	Check remote server for existing web shell
Exploit Details	Display system information and versioning
Remote Server Scan	Check remote server for existing web shell
Remote File Downloader	Download file from remote server via CURL or wget
Hex Encode/Decode	Hex Encode/Decode
FTP Anonymous Access Scaner	Search for Anonymous FTP
Mass Deface	Defacement
Config Grabber	Grab system configuration such as “/etc/passwd”
SymLink	link
Cookie Hijack	Session hijacking
Secure Shell	SSH Shell
Mass Overwrite	Rewrite or append data to the specified file type.
FTP Manager	FTP Manager
Check Steganologer	Detects images with EXIF header
Adminer	Download Adminer PHP database management into the ./tools_ensikology/
PHP Info	Information about PHP’s configuration
Byksw Translate	Character replacement
Suicide	Self-delete

Figure 5. Code listing Ensiko features (Click to enlarge)

Ransomware Analysis

The malware uses PHP RIJNDAEL_128 with CBC mode to encrypt files in a web shell directory and subdirectories and appends filenames with the “.bak” extension. The following code snippet demonstrates this behavior of the malware:

Figure 6. Code showing encryption behavior (Click to enlarge)

Figure 7. Encryption and decryption code (Click to enlarge)

Figure 9. Log of files being encrypted (Click to enlarge)

The malware also drops an index.php file and sets it as the default page using a .htaccess file; the attacker is also notified of this action via email. The following code snippet shows this behavior:

Tool set

To carry out more tasks on an infected system, the malware can load various additional tools onto an infected system. Most of these tools are loaded from Pastebin. The malware creates a directory called tools_ensikology to store these tools.

There is a technique in which a malicious actor hides code within the exchangeable image file format (EXIF) headers of an image file and uses a PHP function called exif_read_data to extract and run this code on an affected server. The steganologer function identifies images with EXIF headers and labels them as a logger. In the following screenshot, test1.jpg and test2.jpg both have EXIF headers with hidden code and are identified s.

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Backdoor Scan

A backdoor scan checks a given remote host for the existence of a webshell from a hardcoded list.

 

 

More information

Source :https://blog.trendmicro.com/trendlabs-security-intelligence/ensiko-a-webshell-with-ransomware-capabilities/