December 9, 2023

Threat researchers have found a new feature-rich malware that can encrypt files on any system running PHP, making it a high risk for Windows, macOS, and Linux web servers.

The malware received the name Ensiko and is a web shell written in PHP. Attackers can use it to remotely control a compromised system and run a host of malicious activities.

Ensiko’s large list of capabilities, the file-encryption component stands out as it can be used for ransomware attacks against servers.

Researchers found that it uses the symmetric Rijnadel-128 cipher in CBC mode to encrypt files.

Ensiko encrypts files in a web shell directory and subdirectories and appends the .BAK extension to processed files.

The malware can be password protected for secure access and avoid a takeover like it happened last week with Emotet when someone replaced the malware payloads with memes.

Authenticating to this web shell is not straightforward. The developer hid the login form on a “Not Found” page. For the analyzed sample, the access key is “RaBiitch.”

To expand capabilities, Ensiko can load several tools, which the malware downloads from Pastebin and stores them in a directory named “tools_ensikology.”

One of the functions of the malware is called Steganologer, which can identify image files that have code in their metadata (EXIF headers). The code is then extracted and executed on the compromised server.

Ensiko can also check if a web shell from a predefined list is present on a remote host. Another scanning function called Remote File Check allows the operator to look for arbitrary files on a remote system.

Another function in this malicious tool allows recursive overwrite of all files with a specified extension in a directory of a web shell.

Ensiko’s capabilities do not stop at this, though. The malware lets threat actors run brute-force attacks on FTP, cPanel, and Telnet, thus enabling them extended access.

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