New Medusa Botnet Emerging Via Mirai Botnet Targeting Linux Users – Cyble

A Botnet Capable of Performing DDoS, Ransomware, and Bruteforce Attacks

Since 2016, Mirai has been an active botnet that targets networking devices running Linux with vulnerabilities. The botnet takes advantage of these vulnerabilities in devices such as routers, IP cameras, and IoT devices to exploit them and gain complete control over the machine. With this control, Mirai can carry out various malicious activities, including Distributed Denial of Service (DDoS) attacks and downloading additional malware.

Cyble Research and Intelligence Labs (CRIL) has been keeping a close eye on the actions of the MiraiBot and monitoring its behavior.

Below are the statistics of the Mirai botnet attacks observed in Jan-2023 through the Cyble Global Sensor Intelligence (CGSI).

Figure 1 – Statistics of Mirai Botnet in January 2023

Recently, CRIL uncovered a variant of the Mirai botnet (sha256: 2491bb75c8a3d3b8728ab46a933cd81f8176c1f9d7292faeecea67d71ce87b5c) that was downloading and propagating a new botnet called the “Medusa Botnet”. When run, the Mirai botnet connects to the command and control server and retrieves the “medusa_stealer.sh” file, which it then executes.

The figure below illustrates the malware’s communication with its Command and Control (C&C) IP address.

Figure 2 Malware Comminucating to the CC IP — Figure 2 – Malware Comminucating to the C&C IP

The downloaded medusa_stealer.sh file contains the commands to download and execute Medusa malware files on Linux machines.

The content of the medusa_stealer.sh is shown below.

Figure 3 Content of medusa stealer.sh File — Figure 3 – Content of medusa_stealer.sh File

At the time of analysis, the download links were unavailable. However, based on the C&C communication pattern, researchers at CRIL were able to identify the Python source code of the Medusa botnet. The technical details section provides an overview of the features of the Medusa botnet, which is written in Python.

Technical Analysis

Medusa Botnet Client

The medusa botnet client receives four parameters: method, IP, port, and timeout, as shown below.

Figure 4 Main Function of Medusa bot client — Figure 4 – Main Function of Medusa bot client

Method: This parameter receives various commands from the C&C server to perform malicious activities such as DDoS attacks, Ransomware, brute force Attack, etc.
IP: IP address of the victim
Port: Port Number of the Victim
Timeout: Timeout of the attack

DDoS Attack

The Medusa Botnet has the ability to launch Distributed Denial of Service (DDoS) attacks on various levels of the network hierarchy, including Layer 3, Layer 4, and Layer 7. These attacks can be carried out either by using spoofed IP addresses or the IP address of the victim’s machine where the client is installed. The botnet employs the spoofer() function to generate random IP addresses, making it challenging for the victims to determine the origin of the DDoS attack.

The figure below illustrates the code for the spoofer() function.

Figure 5 Generates Random IP Address — Figure 5 – Generates Random IP Address

The malware can execute the following DDoS attacks on different levels of the network layer.

SPOOFING ATTACK METHODS	NO-SPOOFING ATTACK METHODS
gre_spoof, icmp_spoof, udp_spoof, syn_spoof, ack_spoof, fin_spoof, rst_spoof, psh_spoof, http_get_flood, http_raw_flood, cloudflare_browser_flood	gre_no_spoof, udp_no_spoof, handshake_no_spoof, ack_no_spoof, fin_no_spoof, rst_no_spoof, psh_no_spoof, syn_no_spoof

Ransomware

The Medusa botnet can launch ransomware attacks on target machines using the MedusaRansomware() function. This function searches all the directories for files with the extensions specified in the “extensions” list and then encrypts them by adding the “.medusastealer” extension to their file name.

The ransomware encrypts the victim files with a Python library that allows files to be encrypted with an AES 256-bit encryption key. It will not encrypt system files and already encrypted files.

The figure below shows the list of extensions targeted in the system by MedusaRansomware.

Figure 6 List of extensions encrypted by Ransomware — Figure 6 – List of extensions encrypted by Ransomware

The below figure shows the code snippet of the MedusaRansomware() function used for file encryption.

Figure 7 Code snippet of Ransomware function — Figure 7 – Code snippet of Ransomware function

The Ransomware also sleeps for 24 hours after encrypting the files and forcefully deletes all the files present in the system drives, as shown below.

Figure 8 Commands to destroy system drives — Figure 8 – Commands to destroy system drives

Finally, the ransomware function displays the ransom note containing instructions to recover the victim’s encrypted files, as shown below.

Figure 9 Medusastealer Ransom note — Figure 9 – Medusa Stealer Ransom note

The ransomware code is designed to display a ransom note after the files have been destroyed, and it appears to be faulty in its implementation.

BruteForce Attack and Additional Payload injection

The medusa bot can carry out bruteforce attacks on Telnet services running on internet-connected devices using the ScanWorld function. It performs a brute force attack and injects an additional payload using the following steps:

It starts by defining two lists, username_scanner, and password_scanner, that contain commonly used usernames and passwords.
It then downloads a payload file “client-tcp” using “wget” (URL: hxxps[:]//medusa-stealer[.]cc/payload/client-tcp) and saves it in the variable infection_medusa_stealer. The download link was unavailable during the analysis, so the exact purpose of “client-tcp” is not yet known.
The function then executes the zmap command to scan for internet-connected devices with Telnet services running on port 23 and stores the results in a file “zmap.txt”.
It then reads the IP addresses from “zmap.txt” and tries to connect to the Telnet services running on those IPs.
The function tries all combinations of usernames and passwords for each IP address from the username_scanner and password_scanner lists.
If a Telnet connection is established, the function sends the malicious payload, infection_medusa_stealer, to the connected system using a bruteforce attack.

The below figure shows the code snippet of the Scanworld() function used for brute-force attacks on Telnet services.

Figure 10 Scanworld function used for brute force attack — Figure 10 – Scanworld() function used for brute-force attack

The Medusa botnet is equipped to receive commands “FivemBackdoor” and “sshlogin”, allowing for backdoor access and SSH login attempts. However, the lack of corresponding code in the client Python file indicates that the Medusa botnet is either still in its development stage or the analyzed files are incomplete.

Exfiltration

The send_data() function is used to collect various information about the system and sends it to the remote server at “hxxps://medusa-stealer[.]cc/add/bot”. The send_data() function calls the all_data_system() function internally, which collects information such as the username, hostname, IP address, operating system, CPU and RAM usage, Total number of CPU cores, and unique identifier of the system. This collected information is stored in a dictionary variable ‘data’ and returned by the function.

The send_data() function further sends the victim’s stolen information to the remote server using the POST method along with a custom “User-Agent” header “medusa-stealer/1.0”. The below image shows the code snippet of the Send_data() function used for Exfiltration.

Figure 11 Code snippet for Exfiltration — Figure 11 – Code snippet for Exfiltration

Conclusion

With the growing popularity of Linux machines, Threat Actors have improved their methods for attacking these systems. In this scenario, the Threat Actors are using the well-known Mirai Linux botnet to drop a new malware called the Medusa botnet, which not only has DDoS capabilities but can also carry out ransomware attack, brute force attack, download additional payload, and steals sensitive information from the victims’ machine.

Our Recommendations

We have listed some essential cybersecurity best practices that create the first line of control against attackers. We recommend that our readers follow the best practices given below:

Avoid downloading pirated software from warez/torrent websites. The “Hack Tool” present on sites such as YouTube, torrent sites, etc., mainly contains such malware.
Use strong passwords and enforce multi-factor authentication wherever possible.
Update and upgrade your computer, mobile, and other connected devices.
Refrain from opening untrusted links and email attachments without first verifying their authenticity.
Educate employees on protecting themselves from threats like phishing/untrusted URLs.
Block URLs that could be used to spread the malware, e.g., Torrent/Warez.
Monitor the beacon on the network level to block data exfiltration by malware or TAs.
Enable Data Loss Prevention (DLP) Solutions on the employees’ systems.

MITRE ATT&CK® Techniques

Tactic	Technique ID	Technique Name
Discovery	T1518.001	Security Software Discovery
Command and Control	T1071	Application Layer Protocol
Command and Control	T1095	Non-Application Layer Protocol
Command and Control	T1571	Non-Standard Port

Indicators of Compromise (IOCs)

Indicators	Indicator Type	Description
2491bb75c8a3d3b8728ab46a933cd81f8176c1f9d7292faeecea67d71ce87b5c	SHA256	Mirai Binary (medusa_stealer.x86)
54c67bb062d73ae9fabf5f0e1e2136e05cb6e69b	SHA1	Mirai Binary (medusa_stealer.x86)
ed64d941fd8603196c0e31ae58c1992d	MD5	Mirai Binary (medusa_stealer.x86)
hxxp://45.145.167[.]117/medusa_stealer.sh	URL	URL Delivering medusa_stealer.sh File
87b5ba7da8aa64721baca0421a01e01bb1f1ca8a2f73daa3ca2f5857e353c182	SHA256	medusa_stealer.sh File
c059eec897c48b81cfc6a6765e176cc88231c31e	SHA1	medusa_stealer.sh File
e3a08ffb7106ece9612d3aa8078a8287	MD5	medusa_stealer.sh File
2f2759b5933f06c9fdbc87ea941e8ef53ea0e3b715afd57de52ed2927d197c33	SHA256	Malicious Python Script (clientv2.py)
088332f4ff6b6a12f094a429d6f60ec500d3d85b	SHA1	Malicious Python Script (clientv2.py)
336674857b5ede1e09daeff1a14adedc	MD5	Malicious Python Script (clientv2.py)
bce94b214a6bae00b03ada34c66210d9143895d6c0be9e21c10e9951cc469fbf	SHA256	Malicious Python Script (clientv2.py)
dc6ea04feb31eb9539f577d7965d0fb925dd7e52	SHA1	Malicious Python Script (clientv2.py)
ed24c7c0b73887e35f1c12ab0dda98fe	MD5	Malicious Python Script (clientv2.py)
48f5f09ddd7089a9397d26e219eb1a1a937c3238f7ecdc7cdfc5383141d77ad9	SHA256	Malicious Python Script (clientv2.py)
3bcbc498de18d91a1d05e428fa94e4145959fbd2	SHA1	Malicious Python Script (clientv2.py)
14655930fab2319ff9cd5187a0caa242	MD5	Malicious Python Script (clientv2.py)
5799ee35a334f839bb666a0136ca2615390d0b7fb6a14875bafbfab3414045e9	SHA256	Malicious Python Script (clientv2.py)
b2134b18e827402378da09a8dcd9da92509e8131	SHA1	Malicious Python Script (clientv2.py)
1eee2293e51b01300c75b649715e472d	MD5	Malicious Python Script (clientv2.py)
medusa-stealer[.]cc	URL	Medusa C&C Server URL

Source: https://blog.cyble.com/2023/02/03/new-medusa-botnet-emerging-via-mirai-botnet-targeting-linux-users/

Tags: IOT, TOOL, BOTNET, EXFILTRATION, BACKDOOR, EMAIL, PHISHING, MOBILE