Command and Control servers, more commonly referred to as C2 or C&C, are a cornerstone in the cybercriminal's arsenal. These servers facilitate near-invisible communication with compromised devices within a targeted network, playing a crucial role in the remote management of digital attacks. Their ability to discreetly transmit orders and orchestrate data theft positions C2 servers as sophisticated and dangerously effective attack vectors.

Nowadays, all malware that penetrates a network by various means (phishing, brute force credentials or credential theft) makes callbacks to a C2 server to take indstructions, download additional components or exfiltrate data.

In the MITRE ATT&CK framework, the involvement of C2 servers at different stages of the attack is one of the most common strategies.

What are the extended functionalities of C2 servers?

Orchestration of complex attacks :

C2 servers do more than coordinate simple phishing attacks. They orchestrate large-scale malicious campaigns, exploiting systemic and human vulnerabilities to infiltrate and compromise networks. These attacks can be diverse, ranging from the deployment of ransomware to the performance of industrial espionage, testifying to their versatility and dangerousness. In the case of DDoS (Distributed Denial of Service) attacks, C2 servers play the role of orchestra conductor or mastermind for the machines in the zombie network.

Targeted order transmission :

The sophistication of C2 servers enables them to transmit specific commands to infected devices, orchestrating actions that go far beyond simple information gathering. They can modify system configurations, deploy additional malicious software, or even take complete control of devices for malicious purposes.
Remote updates and maintenance: In addition to distributing malware, C2 servers can send updates for existing malware, increasing its effectiveness or further camouflaging it from antivirus software. This ability to maintain and update infections remotely makes C2 servers particularly formidable.

Advanced camouflage techniques :

C2 servers use sophisticated methods to remain undetected, including the use of advanced encryption techniques and anonymous networks. This invisibility allows attackers to remain active in a targeted network for long periods, collecting data and executing commands without being detected. Finally, these servers can regularly change domain and IP address, making detection complex.

Here are a few examples:

The CustomerLoader malware uses C2 servers to download advanced compromise payloads.

The infostealer StealC generates URLs for its C2 servers in a totally random and continuous manner, making them very difficult to track.

Statistics and trends :

At this time, we cannot confirm the number of active servers, however the site https://urlhaus.abuse.ch/browse/page/2/ lists nearly 3 million malicious URLs. The constant evolution of C2 servers and their ability to frequently change domains underlines an alarming reality: cybercrime is constantly changing, making the task of defense all the more complex. Available statistics, while representing a fraction of the true scale of the problem, clearly indicate that malicious URLs number in the millions, with each C2 server having the potential to infect and control hundreds, if not thousands, of devices.

According to the Akamai Group, between 10 and 15% of companies in 2022 will have had web traffic linked to communication with C2 servers.

Nevertheless, this number of infected machines is a good indicator of the scale of a threat, and should not be overlooked in the event of an attack.

To detect the early signs of an attack involving a call to C2 servers, it is important to monitor network traffic, as the volume and destination of network traffic generated by infected machines and directed to the Command & Control server can be significant. This unusual traffic can be used to identify and detect malicious activity.

Most of today's serious malware is executed via Command & Control servers, but there are a number of frameworks that enable organizations to understand attackers' methods and be as reactive as possible.

Proactive defense against C2 servers :

In the face of this insidious threat, monitoring network traffic is an essential first line of defense. Identifying anomalous communications with C2 servers enables early detection of infections. The MITRE ATT&CK framework and other strategic tools provide organizations with the means to understand adversaries' tactics and develop appropriate responses to protect their critical infrastructures.

If our peers have been able to define knowledge bases enabling us to increase our defensive capabilities against attacks using Command & Control servers, it's because the number of such attacks is indeed significant. 

Olfeo: A response to the C2 threat :

In this context, Olfeo stands out for its proactive approach to cybersecurity. By blocking access to unknown and potentially malicious domains, Olfeo creates a secure digital environment, preventing malicious communications from their initial attempt.

Olfeo's Trust-Centric technology, combined with a database continually enriched by artificial intelligence and a dedicated team, ensures secure browsing while facilitating access to the legitimate resources needed for day-to-day business operations. In particular, this approach solves the problem of detecting C2 servers whose domains may change regularly.

Conclusion:

The ubiquity and increasing sophistication of Command and Control servers represent a major challenge to global digital security. However, the adoption of advanced defense strategies, combined with innovative cybersecurity solutions such as those offered by Olfeo, offers an effective solution. By interrupting malicious communication chains and preventing vulnerabilities from being exploited, we can not only detect but also neutralize the threats posed by C2 servers, protecting critical infrastructures and sensitive data from malicious actors.