How Remote Access Trojans (RATs) Work: Anatomy of a Stealthy Cyber Threat

To understand how RATs work, let’s break down their lifecycle into key stages: infiltration, installation, communication, and execution.

1. Infiltration: How RATs Enter a System

The first step in a RAT attack is gaining access to the victim’s system. Attackers use a variety of methods to deliver RATs, including:

• Phishing Emails:
  Attackers send emails disguised as legitimate messages, often containing malicious attachments or links. When the victim opens the attachment or clicks the link, the RAT is downloaded and installed.

• Malicious Downloads:
  RATs can be hidden in pirated software, games, or other downloadable files. Users who download and install these files unknowingly infect their devices.

• Exploiting Vulnerabilities:
  Attackers exploit security vulnerabilities in software or operating systems to deliver RATs without user interaction. For example, they might use a known vulnerability in a web browser to install the RAT when the victim visits a compromised website.

• Social Engineering:
  Cybercriminals use psychological manipulation to trick users into installing RATs. For example, they might pose as tech support and convince the victim to download a “necessary update” that is actually a RAT.

• Removable Media:
  RATs can be spread through infected USB drives or other removable media. When the victim plugs the device into their computer, the RAT is automatically installed.

2. Installation: Gaining a Foothold

Once the RAT has infiltrated the system, it needs to install itself and establish persistence. This involves:

• Dropping Payloads:
  The initial file that delivers the RAT (often called a “dropper”) extracts and installs the main RAT payload onto the victim’s system.

• Modifying System Settings:
  To ensure it remains active, the RAT may modify system settings, such as adding itself to the startup folder or creating new registry entries. This allows the RAT to restart automatically whenever the system boots up.

• Disabling Security Software:
  Some RATs are designed to disable antivirus programs or firewalls to avoid detection.

3. Communication: Connecting to the Attacker

After installation, the RAT establishes a connection with the attacker’s command-and-control (C2) server. This communication channel allows the attacker to send commands to the RAT and receive data from the infected system. To avoid detection, RATs often use stealthy communication techniques, such as:

• Encrypted Traffic:
  Encrypting the data exchanged between the RAT and the C2 server makes it harder for security tools to detect malicious activity.

• Domain Generation Algorithms (DGAs):
  Some RATs use DGAs to generate a list of random domain names for communication. This makes it difficult for security researchers to block the C2 servers.

• Legitimate Services:
  RATs may use legitimate services like cloud storage platforms or social media sites to communicate with the attacker, blending in with normal traffic.

4. Execution: Carrying Out Malicious Activities

Once the connection is established, the attacker can remotely control the infected system. Common activities include:

• Data Exfiltration:
  The RAT can steal sensitive data and send it back to the attacker. This might include passwords, financial information, or confidential documents.

• Surveillance:
  The attacker can monitor the victim’s activity by capturing keystrokes, taking screenshots, or activating the webcam and microphone.

• System Manipulation:
  The attacker can execute commands on the infected system, such as deleting files, installing additional malware, or disrupting operations.

• Lateral Movement:
  The RAT can spread to other devices on the same network, creating a larger attack surface and increasing the potential damage.