Cactus Ransomware: What You Need to Know

Cactus Ransomware is a formidable threat targeting large commercial organizations. This strain has drawn attention for its advanced evasion tactics against antivirus measures and its ability to exploit known vulnerabilities in VPN appliances to gain initial network access. 

In this comprehensive article, we will explore the Cactus ransomware variant in detail and provide information on the indicators of compromise (IOC) associated with the group’s activity. 

Understanding which industries the ransomware targets and how it operates is essential to improve your cybersecurity and ransomware defenses. 

Cactus ransomware overview

In March 2023 experts get the first signs of Cactus ransomware. The threat emerged as it targeted high-profile organizations, leaving a trail of encrypted files and a distinctive “.cts1” extension, though the trailing number varies between incidents. Its evolution reflects an ongoing effort to stay ahead of security measures, making it particularly challenging to combat.

Cactus is classified as a multifaceted threat, falling into categories such as Ransomware, Crypto Virus, Files Locker, and engaging in double extortion. The group strategically targets VPN appliances, exploiting vulnerabilities for initial access. 

By encrypting files and demanding ransoms, along with double-extortion tactics involving the theft of sensitive data, the cybercriminals seek financial gain.

Cactus encrypts files with AES through the OpenSSL library and protects each key with an embedded RSA public key. It also encrypts its own binary, helping it evade antivirus and network monitoring tools.

How to identify Cactus ransomware: Main IOCs

Indicators of compromise (IOCs) are forensic data points that help identify malicious activity or malware associated with a cyberattack. They include the encryption extension, file hashes, and IP addresses, among other details cybercriminals leave as they infect a machine or system. 

Important: Some of these indicators require technical knowledge of the infected system, so you may need to contact your IT team or a digital forensics service provider.

Cactus ransomware-specific IOCs include:

File Extensions:

• .cts1 (the trailing number can vary; .cts0 marks files caught mid-encryption)

Ransom Note:

• Filename: cAcTuS.readme.txt

Detection Names:

• Avast: Win64:Trojan-gen
• Emsisoft: Generic.Ransom.Cactus.A.6A6CBCEA (B)
• Kaspersky: Trojan-Ransom.Win32.Cactus.d
• Sophos: Mal/Generic-S
• Microsoft: Ransom:Win32/Cactus.LKV!MTB

If you can’t identify the ransomware strain through its IOCs, you can use Proven Data’s free ransomware ID tool to check if the Cactus ransomware is the malware that encrypts your files.

How Cactus ransomware works

Understanding how Cactus ransomware operates is crucial for implementing effective preventive measures and developing strategies for mitigating its impact. In the following step-by-step description, we will delve into the intricacies of Cactus ransomware, shedding light on its infection vectors, encryption process, and the implications for affected systems and data. 

1. Initial Access

A Virtual Private Network (VPN) is a technology that establishes a secure and encrypted connection, or “tunnel,” between a user’s device and a remote server. The primary purpose of a VPN is to ensure the confidentiality and integrity of data transmitted over the Internet, especially when using public networks. 

Cactus ransomware gains entry into systems by exploiting vulnerabilities in Virtual Private Network (VPN) appliances.

VPN providers release updates to patch security vulnerabilities and improve overall performance. Regularly check for updates and apply them promptly.

2. Exploitation

Once inside the network, Cactus ransomware employs lateral movement, spreading across devices within the network. It takes advantage of weaknesses in network security, including weak passwords or unpatched software, to gain control over multiple machines.

3. Execution

Cactus utilizes several tools such as Chisel, Rclone, TotalExec, and Scheduled Tasks to carry out its malicious activities. These tools help the ransomware establish persistence on infected systems, ensuring it can continue its operations even after a system reboot.

4. Data Theft

Before encrypting files, Cactus ransomware exfiltrates sensitive data from compromised systems. It later uses this stolen data as leverage for further extortion or may sell it on underground forums.

5. Encryption

Cactus ransomware employs unique encryption techniques to encrypt the victim’s files. It encrypts files with AES and wraps each key with the attacker's RSA public key, so recovery without the attacker's private key isn't feasible. Notably, the ransomware encrypts its own code, enhancing its ability to evade detection by antivirus and network monitoring tools.

6. Ransom Note

After completing the encryption process, Cactus ransomware leaves a ransom note named “cAcTuS.readme.txt.” This note provides instructions on how victims can negotiate with the attackers, typically directing them to TOX chat, an encrypted messaging platform.

Important: Do not pay the ransom. Paying the ransom does not guarantee that you will get your data back, and it may encourage the attackers to continue their criminal activities. Check our in-depth article on what happens if you pay the ransom.

How to handle a Cactus ransomware attack

Handling a ransomware attack can be complex and requires expertise. Therefore, it is recommended to contact an emergency incident response team such as Proven Data to contain the attack and assess recovery options.

You can also report the attack to law enforcement agencies like the FBI and cybersecurity organizations to help prevent future attacks and catch the perpetrators.

We strongly recommend contacting cybersecurity services to handle ransomware attacks. Proven Data technicians not only retrieve ransomware-encrypted data but also create forensic reports and streamline incident response, minimizing your business downtime and financial loss.

How to prevent ransomware attacks

Preventing Cactus ransomware attacks is always the best cybersecurity tactic. If you are a recent victim, you must follow these tips to avoid a new ransomware attack:

Keep your software up to date

Regularly update your operating system and programs to uphold security standards. Reputable OS providers regularly check their software for vulnerabilities and patch security issues to protect against newly detected threats.

Use reputable antivirus software

Employ reputable antivirus software to bolster protection against malware significantly, and regularly check that it is updated. You can also check your network for vulnerabilities and learn where you need to improve your security system.

Be cautious of suspicious emails

Even though there are no known cases of Cactus using phishing as an attack method, it’s important to exercise caution when dealing with emails from unfamiliar or dubious origins. Refrain from opening files or clicking on links within emails that you are not expecting or that seem suspicious.

Do not download cracked software

Cracked software is the term used to describe illicitly modified or pirated versions of commercial software, typically distributed without proper authorization or licensing. Cybercriminals often hide ransomware executables on cracked-software distribution websites, leading users to unwittingly download and run the malware.

Backup your data

Regularly back up your data to an external hard drive or cloud storage service to prevent complete data loss in case of a ransomware attack. A highly recommended strategy for data loss prevention is the 3-2-1 backup strategy.

The 3-2-1 backup strategy involves creating three total copies of your data: two on different media and one offsite, ensuring redundancy and protection against data loss. And at least one copy offsite to prevent loss due to natural disasters or other local incidents.

Educate yourself and your teams

Educate yourself and your employees about ransomware risks and how to avoid them, such as avoiding suspicious emails or downloads.

Consult cybersecurity professionals

Proven Data offers cybersecurity services to help you keep your data protected against threat actors. From vulnerability assessments to ensure your systems and servers don’t have open doors for cyberattacks, to Incident Response (IR) services for immediate action after a successful attack.