Pivoting in Internal Networks

Pivoting in Internal Networks: Traversing the Labyrinth

Introduction

In the realm of cybersecurity, gaining initial access to a network is often only the first step for an attacker. To reach their target – be it sensitive data, critical infrastructure, or specific systems – they frequently need to move laterally within the network. This process, known as pivoting, involves leveraging a compromised system as a stepping stone to access other systems that might not be directly accessible from the attacker's initial foothold. Pivoting is a crucial technique for penetration testers to simulate real-world attack scenarios, and for defenders to understand potential attack paths.

This article delves into the concept of pivoting in internal networks, outlining its prerequisites, advantages, disadvantages, features, and techniques, providing code snippets where relevant to illustrate practical implementation.

Prerequisites for Pivoting

Before embarking on a pivoting operation, certain prerequisites must be met. These are foundational to successfully navigating the internal network:

1. Compromised System (Pivot Point): The cornerstone of pivoting is a compromised system within the network. This system serves as the launchpad for further exploration and exploitation. The type of access gained to this system significantly influences the pivoting options available. Local administrator privileges are generally preferred for installing tools and configuring routing, but even user-level access can be valuable.

2. Network Connectivity: The compromised system must have network connectivity to other systems within the target network. This includes the ability to communicate over various protocols, such as TCP, UDP, and ICMP. If the compromised system is segmented or heavily firewalled, pivoting becomes significantly more challenging.

3. Local Reconnaissance: Gathering information about the internal network from the compromised system is crucial. This involves identifying network segments, IP address ranges, active services, and other hosts. Common tools for this purpose include ipconfig (Windows), ifconfig (Linux/Unix), netstat, nmap, arp, and custom scripts.

4. Credentials (Optional but Highly Beneficial): Acquired credentials from the compromised system, such as stored usernames and passwords, can be leveraged to gain access to other systems. This can significantly streamline the pivoting process and allow for more discreet access. Tools like Mimikatz (Windows) are often used for credential extraction.

5. Pivoting Tools: Appropriate tools need to be installed on, or accessible through, the compromised system. These tools enable the attacker to tunnel traffic, perform port forwarding, and conduct further reconnaissance. Examples include SSH tunnels, Metasploit's Meterpreter, socat, and specialized pivoting frameworks.

Advantages of Pivoting

Pivoting offers several advantages, both for attackers and penetration testers:

• Bypassing Network Segmentation: Pivoting allows access to systems that are not directly reachable from the outside network due to firewalls or network segmentation. By hopping through the compromised system, these security measures can be circumvented.
• Hiding Origin: The true origin of an attack can be masked, making attribution more difficult. The compromised system acts as an intermediary, obscuring the attacker's source IP address.
• Exploiting Internal Trust Relationships: Internal systems often trust each other more than they trust external systems. Pivoting leverages this trust to gain access to sensitive resources. For example, a database server might trust connections originating from a web server, even if that web server has been compromised.
• Access to Internal Resources: Pivoting provides access to internal resources such as databases, file servers, and applications that are not exposed to the internet. This can be crucial for data exfiltration or further compromise.
• Increased Attack Surface: By gaining access to more systems, the attacker expands their attack surface within the network. This increases the likelihood of finding vulnerabilities that can be exploited for further lateral movement.

Disadvantages of Pivoting

Despite its advantages, pivoting also presents some challenges:

• Performance Bottlenecks: Traffic must be routed through the compromised system, which can create a performance bottleneck, especially if the system has limited resources or network bandwidth.
• Increased Risk of Detection: Pivoting activities often generate unusual network traffic patterns, which can be detected by intrusion detection systems (IDS) or security information and event management (SIEM) systems.
• Complexity: Setting up and managing pivoting infrastructure can be complex, requiring a thorough understanding of network protocols and security tools.
• Dependence on Compromised System: The success of pivoting depends entirely on the compromised system remaining operational. If the system is detected and taken offline, the pivoting operation is disrupted.
• Tool Dependency: Pivoting is often reliant on specific tools that may be blocked or detected by security software. The attacker must be prepared to adapt and use alternative tools.

Features of Pivoting Techniques

Several features distinguish different pivoting techniques. Understanding these features helps in selecting the most appropriate technique for a given situation:

• Port Forwarding (SSH Tunneling): This is a common technique used to forward traffic from a local port on the attacker's machine to a remote port on a system accessible through the compromised system. SSH provides encryption for secure port forwarding.

   ssh -L 8080:target_system:80 user@compromised_system

This command forwards traffic to port 8080 on the attacker's local machine to port 80 on target_system, which is accessible through compromised_system.

• Proxying: A proxy server on the compromised system can be used to route all traffic from the attacker's machine through the compromised system. Tools like socat can be used to create simple proxy servers.

   socat TCP-LISTEN:8080,fork TCP:target_system:80

This command listens on port 8080 and forwards traffic to target_system on port 80.

• Reverse Port Forwarding: This is used when the attacker's machine is behind a firewall and cannot initiate connections to the compromised system. The compromised system initiates a connection to the attacker's machine and forwards traffic through that connection.

   ssh -R 8080:localhost:80 user@compromised_system

This command configures the compromised_system to listen on its port 8080 and forward traffic to the attacker's machine on port 80 (localhost in the context of the reverse tunnel).

• Double Pivoting: In complex scenarios, multiple pivoting steps may be required to reach the target system. This involves compromising a system, using it to compromise another system, and repeating the process until the target is reached.

• Dynamic Port Forwarding (SOCKS Proxy): This allows the attacker to create a SOCKS proxy server on the compromised system. The attacker can then configure their applications to use this proxy, allowing them to access a wide range of services on the internal network.
  

   ssh -D 1080 user@compromised_system

This command creates a SOCKS proxy server on port 1080.

Pivoting Tools and Frameworks

Several tools and frameworks facilitate pivoting:

• Metasploit Framework: Metasploit's Meterpreter payload offers powerful pivoting capabilities, including port forwarding, proxying, and routing. It also provides a wide range of post-exploitation modules for further compromise.
• SSH: SSH is a versatile tool for creating secure tunnels for port forwarding and proxying. It's often pre-installed on Linux and Unix systems.
• Socat: Socat is a powerful command-line utility for establishing bidirectional data transfer between two endpoints. It can be used for port forwarding, proxying, and other network manipulation tasks.
• Chisel: A fast TCP tunnel, transported over HTTP, secured via SSH.
• Proxychains: Proxychains forces any TCP connection made by any given application to follow a chain of proxies. It supports different proxy types such as HTTP, SOCKS4, and SOCKS5.

Conclusion

Pivoting is a crucial technique for attackers and penetration testers alike. By leveraging compromised systems as stepping stones, it allows access to otherwise unreachable resources and expands the attack surface within a network. Understanding the prerequisites, advantages, disadvantages, features, and available tools is essential for effectively performing and defending against pivoting attacks. As networks become increasingly complex and segmented, pivoting will continue to be a vital skill for both offensive and defensive security professionals. Defenders should focus on hardening systems, implementing strong network segmentation, and monitoring for suspicious activity to mitigate the risk of pivoting attacks. Regular vulnerability assessments and penetration testing exercises are also crucial for identifying and addressing potential weaknesses in the network security posture.