How does Cerber work?

Cerber is a ransomware virus that was first observed in early 2016. It is considered one of the most dangerous ransomware threats active today due to its sophisticated encryption methods and active development (Security Intelligence). Cerber encrypts files on infected Windows systems and demands a ransom payment in bitcoin in order to decrypt them. It utilizes both ransomware-as-a-service and affiliate programs to maximize infections.

Cerber has continuously enhanced its capabilities since it first emerged. It leverages complex anti-analysis and anti-detection techniques to avoid security software. Each new version of Cerber has introduced additional features, making it more evasive and destructive. Overall, Cerber is regarded as one of the most advanced and concerning ransomware families today due to its active development and far-reaching campaigns (Cylance).

Infection Methods

Cerber primarily spreads through malicious email attachments that contain malware-laden Microsoft Office documents or compressed files. When users open these attachments, exploit kits or macro code execute to download the Cerber malware files onto the victim’s computer [1].

One technique Cerber uses is sending emails with .js or .hta attachments that contain JavaScript or VBScript code to download the malware payloads. Another common method is using Microsoft Office documents infected with malicious macros that run when opened. The macro code reaches out to domains hosting exploit kits to compromise the system and download Cerber [2].

In addition to email attachments, Cerber is distributed through exploit kits on compromised websites utilizing drive-by downloads. When a user visits the infected site, the exploit kit scans for vulnerabilities and silently installs Cerber without any action from the user [3].

Encryption Process

The encryption process is one of the key components of how Cerber operates and causes damage. Cerber uses a combination of RSA and AES encryption algorithms to rapidly encrypt a victim’s files (Malpedia). The malware first generates a pair of RSA public and private keys. The public key is used to encrypt the AES key that will encrypt the actual files. The RSA private key remains with the malware authors to eventually decrypt files if a ransom is paid.

During encryption, Cerber systematically traverses the infected system’s drives and encrypts several hundred file types, focusing on documents, images, audio, video, emails, and source code. It adds extensions like .cerber, .cerber2, .cerber3 to each encrypted file. The encryption process is extremely fast, capable of encrypting gigabytes of data within minutes or hours (Blackberry). This speed prevents victims from quickly reacting and isolating their systems once the attack begins.

Ransom Demands

Cerber ransomware initially demanded ransoms of 1.24 bitcoins, or around $500 at the time, according to Proofpoint [1]. The ransom amount has steadily increased over time. In 2016, Cerber demanded 1.5 to 3 bitcoins, or $1,000 to $3,000. By 2017, the ransom amount rose to 5 bitcoins, or around $5,000 at the time [2].

Once a victim’s files are encrypted, Cerber displays a ransom note with payment instructions. The ransom note is displayed as a text file and explains that the victim’s files were encrypted and how to purchase bitcoins to pay the ransom. Early versions of Cerber played an audio message speaking the ransom note text [3]. The ransom note provides a personal page on the Tor network where victims can enter the decryption key after paying.

Cerber accepts ransom payments in bitcoin cryptocurrency. Victims are instructed to purchase bitcoins through services like and then transfer the bitcoins to the bitcoin wallet address provided on the ransom note page on Tor.

Decryption Challenges

One of the biggest challenges with Cerber ransomware is the lack of decryption tools. Unlike some other ransomware strains, there are currently no free decryption utilities available for Cerber (Source). The criminals behind Cerber are very careful to delete any decryption keys after the time limit expires or if an attempt is made to circumvent the ransom payment (Source).

This presents a major obstacle for victims whose files have been encrypted. Without access to the unique decryption keys held by the attackers, it is virtually impossible to recover encrypted files. Experts recommend avoiding paying the ransom if possible, as there is no guarantee files will be decrypted. However, the lack of decryption options leaves victims with limited alternatives.

Cerber’s strong encryption coupled with the deletion of keys makes recovering files through conventional methods very challenging. Users are advised to have good backups in place to restore encrypted data if impacted by a Cerber infection.

Anti-Analysis Techniques

Cerber utilizes several techniques to evade analysis and make reverse engineering more difficult for security researchers. This includes packing, anti-debugging, and anti-virtualization methods.

Packing refers to compressing or encrypting the malware code to hide it from antivirus engines and other detection methods. Cerber is packed with a custom packer that security firm Hexacorn analyzed in detail here.

Anti-debugging techniques detect when the malware binary is executed in a debugger and can terminate execution or employ other deception methods. Cerber checks for the presence of common debuggers like OllyDBG and uses other anti-debug tricks detailed in this analysis.

Anti-virtualization looks for signs the malware is running in a virtual machine rather than on a real system. Cerber uses several techniques to detect virtual environments and sandboxes, making analysis in VM environments difficult, as covered in this report.

Command and Control

Cerber utilizes various methods for command and control (C2) communication with the operators behind the ransomware. According to research from Cyber Threat Intelligence [1], Cerber initially used HTTP for C2 but later versions switched to UDP for increased stealth. Specifically, Cerber communicates with C2 servers via UDP port 6892 [2]. An analysis of the Cerber infrastructure shows the ransomware reaching out to a series of domains hardcoded into the malware [3]. These domains act as proxies to obscure the true C2 servers. Cerber relies on Domain Generation Algorithms (DGAs) to dynamically generate domain names for resiliency. If one C2 domain is taken down, the malware simply tries the next DGA-generated domain.

Notable Campaigns

In March 2017, a massive spam campaign called Blank Slate spread Cerber ransomware to victims globally. The attackers registered new domains as soon as they became available and used them to send waves of spam messages with Cerber hidden inside Microsoft Office document attachments (Blank Slate Spam Campaign Spreads Cerber Ransomware). This campaign impacted thousands of victims across various industries and countries.

Another large Cerber campaign in 2020 exploited a vulnerability in Atlassian Confluence to infect targets. This campaign successfully compromised over 2,000 Confluence servers by exploiting CVE-2022-26134 (Cerber Ransomware Exploits CVE-2023-22518). Many notable companies and organizations were severely impacted, with some reporting losses of millions of dollars due to data encryption and ransom demands.

In addition to campaigns targeting vulnerabilities, Cerber operators have continuously evolved their social engineering and distribution tactics. This includes malicious scripts, fake resumes, delivery order scams, and other techniques to maximize the ransomware’s reach (Cerber Crypto-Ransomware Now Uses Malicious Script Files). Overall, Cerber has cemented itself as one of the most widespread and damaging ransomware strains over the past several years.

Mitigation Strategies

There are several key ways to mitigate the impact of a Cerber ransomware attack and improve the chances of recovery:

Backups are vital to recovering encrypted files after an attack. Regular backups to disconnected devices or cloud services ensure access to clean file versions that can be restored after cleanup. Air-gapped backups are ideal as Cerber cannot reach external drives that are disconnected from infected systems. Testing backups regularly also helps verify that files can be successfully recovered when needed.

Security software that incorporates behavioral analysis and machine learning can detect and block ransomware activity. Solutions that monitor system changes and flag unauthorized encryption events provide protection against Cerber infestations. Perimeter defenses like firewalls can further reduce the risk of malicious traffic reaching endpoints.

User education helps prevent risky activities that enable ransomware. Training staff to identify social engineering attacks, unsafe links and attachments diminishes the chances of Cerber gaining access. Instituting least privilege access and separating privileges can also limit damage if credentials are compromised.

According to security experts, combining robust backups, advanced endpoint protection, access controls and user education provides the most effective ransomware resilience against threats like Cerber (TrendMicro, 2023).

The Future of Cerber

Security experts predict that Cerber will continue to evolve in sophistication and scale. According to Trend Micro, Cerber developers are actively updating the malware to add new capabilities and evade detection (1). For example, Cerber has implemented a fast-changing hash mechanism that generates new hashes every 15 seconds, making traditional signature-based detection ineffective (2).

Experts predict Cerber will continue to be offered as Ransomware-as-a-Service, allowing more cybercriminals to easily deploy it. It may also increase integration of evasion techniques like anti-analysis and anti-sandboxing. Ransom amounts are likely to keep rising as well. To combat these trends, organizations will need advanced behavior-based detection, proactive threat hunting, and comprehensive backup/recovery strategies.