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What is a Command and Control Server? How Does It Control a Compromised System?
A Command-and-Control (C&C) server is used by an attacker or cybercriminal to deliver orders to malware-infected devices and receive stolen data from a target network. Many campaigns have been discovered employing cloud-based services as C&C servers to blend in with normal traffic and evade detection, such as webmail and file-sharing applications.
The headquarters or command centers where malware employed in targeted attacks reports back, allowing stolen data or damaging commands to be retained, are known as C&C servers. Establishing C&C links is essential for attackers to move laterally within a network. C&C servers also function as the command and control center for botnet computers. It may be used to transmit commands that can be used to steal data, propagate malware, disrupt online services, and more.
Botnet command and control systems can employ one of three models: centralized, peer-to-peer [P2P], or random. Aside from allowing attackers to steal data, having C&C software on a server might cause legitimate applications to fail and future resources to be misused.
In the recent decade, malicious network assaults have become more common. Command and control, often known as C2 or C&C, is one of the most destructive assaults, which is frequently carried out using DNS. The attacker begins by infecting a machine that may or may not is protected by a firewall.
Through a phishing e-mail that convinces the recipient to click on a link to a malicious website or open an attachment that executes malicious malware.
By exploiting security flaws in browser plugins.
Through the use of infected software.
After establishing connectivity, the infected system sends a signal to the attacker's server, asking for its next command. The infected machine will carry out the attacker's C2 server's orders and may also install other malware. The attacker now has full control over the victim's computer and can run whatever code he wants.
The harmful virus will often propagate to other machines, forming a botnet (a network of infected computers). An attacker who isn't granted access to a company's network can take full control of it this way.
How Does a C&C Server Exploit a Compromised System?
A C&C server can exploit a compromised system in the following ways −
Theft of Personal Information
Financial papers and other sensitive firm data can be copied or transmitted to an attacker's site.
Shutdown
An attacker can bring down a company's network or shut down one or more devices.
Reboot
Infected systems may shut down and reboot regularly, causing disruption to normal corporate activities.
Distributed Denial of Service
By flooding the servers or networks with internet traffic, DDoS assaults overwhelm them. An attacker can tell each bot in the botnet to make a request to the specific IP address, causing traffic congestion for the targeted server. As a result, genuine traffic to the attacked IP address is refused access, similar to traffic clogging a freeway. This form of assault can be used to bring down a website.
Using Fake Domain Names That Appear to be Authentic
The use of domain names that resemble a pattern of genuine software or e-mail services, replicating typical naming of online advertisement services or sites that are relevant to a current campaign, is one of the most prevalent tactics used for building C&C servers.
How Do C&C Servers Conceal Their Location
APT organizations frequently employ intermediary servers to boost the stealth and availability of C&C servers (also known as proxies). These servers act as proxies, masking the Command and Control server's true destination.
The use of dynamic DNS services such as VoIP, DynDNS, and others is a well-known strategy for concealing C&C locations. Because no real contact information is required to register domain names using these providers, attackers may remain anonymous. In addition, domain names and IP mappings can be altered fast if the target's infrastructure blocks the initial IP. Short caching (TTL) settings connected with such domains make this possible.
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