Remote Control - secuguru/security-terms GitHub Wiki

Remote control techniques allow attackers to gain control over a compromised system, enabling them to execute commands, exfiltrate data, or install additional malware. Remote control methods include remote code execution (RCE), bind shells, and reverse shells. These techniques are commonly used in the later stages of an attack, once initial access has been established.

1. Remote Code Execution (RCE) and Privilege

• Definition: Remote Code Execution (RCE) occurs when an attacker is able to remotely execute commands on a target system, typically through a vulnerability in software or applications. RCE exploits can allow attackers to run arbitrary code with the same privileges as the application being exploited.
• Privilege Levels:
  • User Privileges: If the code executes with user privileges, the attacker may be limited in their ability to access system resources and files.
  • Administrative Privileges: If the RCE exploit gives administrative or root privileges, the attacker gains unrestricted control over the system, allowing them to install additional tools, manipulate system settings, and move laterally within the network.
• Security Implications: RCE is a highly dangerous vulnerability, as it allows attackers to bypass authentication and execute commands directly on the system. The impact of RCE depends on the privilege level attained, with administrative RCE posing the highest risk.

2. Bind Shell

• Definition: A bind shell is a type of shell that opens a port on the target machine and listens for incoming connections from the attacker. Once the connection is established, the attacker can issue commands on the compromised system.
• How It Works:
  • Opening a Port: The compromised system opens a specific port and waits for an incoming connection.
  • Attacker Connects: The attacker connects to the open port using a client (like Netcat), gaining command-line access to the compromised system.
• Security Implications: Bind shells can be detected by monitoring for unusual open ports or listening services on a system. Firewalls and intrusion detection systems (IDS) can help detect or block bind shells, especially if the open port is uncharacteristic for that device.

3. Reverse Shell

• Definition: In a reverse shell, the compromised system initiates a connection back to the attacker’s system. This allows the attacker to bypass certain firewall restrictions, as outgoing connections are typically less restricted than incoming ones.
• How It Works:
  • Connection Back to C2: The compromised system connects to a port on the attacker’s command-and-control (C2) server.
  • Attacker Gains Access: Once connected, the attacker can issue commands on the compromised system, much like with a bind shell.
• Security Implications: Reverse shells are harder to detect and block than bind shells, as they exploit outbound connections that are often allowed through firewalls. Network monitoring for unusual outbound connections and IDS rules can help detect reverse shell activity.

Comparing Bind Shells and Reverse Shells

Aspect	Bind Shell	Reverse Shell
Connection	Target system waits for an incoming connection	Target system initiates a connection to attacker
Firewall Evasion	More easily blocked by firewalls, as it requires an open port	Easier to bypass firewalls, as outbound connections are often allowed
Usage	Commonly used in simpler setups; easy to detect	Preferred for bypassing firewall restrictions

Summary

• Remote Code Execution (RCE) enables attackers to execute arbitrary commands remotely, with the impact dependent on the privileges gained. RCE exploits can grant either user-level or administrative access.
• Bind Shells create a listening service on the target machine, waiting for the attacker to connect, which can be blocked by firewalls but provides direct access once established.
• Reverse Shells initiate a connection from the target to the attacker’s C2 server, allowing attackers to bypass firewall restrictions on incoming connections.

Remote control techniques are powerful tools in an attacker’s arsenal, enabling continued control over compromised systems. To defend against these methods, organizations should prioritize patching vulnerabilities that allow RCE, use firewalls to block unusual connections, and monitor network traffic for signs of unauthorized connections, especially to external C2 servers.