Beware of Phobos Ransomware Delivered via Office Document

Researchers discovered an Office document with a VBA script intended to spread the Phobos ransomware known as FAUST. The FAUST version can sustain persistence in a given environment and generates multiple threads for efficient execution. 

A well-known family of malicious malware called Phobos ransomware is created to encrypt files on a victim’s PC. Since being introduced in 2019, it has taken part in multiple cyberattacks. 

Usually, this ransomware adds an encrypted file with a unique extension on the computer and requests a cryptocurrency ransom for decryption.

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The attackers used the Gitea service to save multiple files encoded in Base64, each containing a malicious binary. These files start a file encryption attack when they are injected into the memory of a system.

Phobos Ransomware Spreading Via Office Document

According to Fortinet analysis, the XLAM document that was found has a VBA script embedded in it. PowerShell is launched by the script when the document is opened.

The data is then downloaded from Gitea in Base64 encoding, which can be decoded to create a clean XLSX file. After that, this file is automatically opened and saved in the TEMP folder, tricking users into believing that the process is finished and safe to use.

The attacker creates a region of memory in the target process, adds malicious code, and makes a call to the entry point of the payload.

The FAUST ransomware, a variant of phobos family, creates info.txt and info.hta files inside the directories containing the encrypted files and appends the “.faust” extension to every encrypted file. These files are used as a way to get in touch with the attackers to start ransom negotiations.

Similar to how Phobos versions typically behave, the FAUST ransomware retains the decryption function for configuration.

“It also initiates multiple threads to perform various tasks. These tasks include deploying encryption, scanning logical drives, searching for network/sharing resources, scanning files individually, and explicitly seeking database-related files”, Fortinet Shared with Cyber Security News.

Final Words

The threat actor was also using a fileless attack to deploy shellcode onto the victim’s machine, which allowed the final FAUST payload to be delivered.

EKING and 8Base are two of the ransomware variants from the Phobos family that FortiGuard Labs has discovered and documented.

Hence, users need to be cautious and not open document files from unknown sources to protect their devices from possible malware threats.