Post-exploitation is the art of the 'what next?' for cyber attackers, a critical phase where they leverage access to dig deeper, escalate privileges, and extract valuable data.
First Published 29th February 2023
Post exploitation.
4 min read | Reflare Research Team
Imagine yourself as a new junior red-team member. Over the past several months, you have learned the art of scanning and mapping target networks. You have also received certification acknowledging your prowess in not only finding heap overflow vulnerabilities using AFL fuzzer, but also in mastering the art of exploit writing.
Now, here is the problem. You know how to find vulnerabilities and exploit them, but once you get your foot into the target network – what do you do after that? So, you asked your senior – and he said to you, “My friend, now is the fun part. Now is the time for post-exploitation.”
Post-exploitation, a term frequently mentioned in cybersecurity circles, refers to the series of actions that attackers undertake after gaining initial access to a computer system or network. This phase is critical as it determines the actual impact of a breach, ranging from data theft to persistent access for future attacks. In this article, we aim to demystify the concept of post-exploitation and introduce key terms associated with it.
What is Post-Exploitation?
Post-exploitation represents the actions carried out by an attacker after successfully breaching a system's defences. Unlike initial access, which focuses on breaching the perimeter, post-exploitation is about what the attacker does once inside. This can include escalating privileges, stealing data, installing backdoors, or spreading to other systems.
This is the phase where the depth of an attacker's skills and tools come into play, and the choice of actions largely depends on the attacker's objectives and the opportunities presented by the compromised system.
Tools such as Empire and Meterpreter – a payload within the Metasploit framework – offer extensive capabilities for post-exploitation, including privilege escalation, lateral movement, and persistence (we will explain what these fancy words mean in a bit).
Empire, for example, is known for its PowerShell and Python agents that enable a wide range of tactics from executing commands to exfiltrating data, all while maintaining stealth.
Meterpreter, on the other hand, provides a dynamic, in-memory execution platform that allows attackers to manage the compromised system, pivot to other systems, and access the network's resources without writing to the disk, thereby evading detection.
However, for the purposes of this article, we will not delve into the specifics of these tools. Our focus is to provide a high-level overview of the post-exploitation phase by introducing the key jargon and concepts associated with it.
Key Terms in Post-Exploitation
In discussing post-exploitation, it is crucial to understand the commonly used terms you will likely encounter among colleagues or industry peers. Therefore, we have compiled a list of essential jargon, aiming to explain the terms and highlight the key differences between those that might initially seem similar.
Privilege Escalation: Privilege escalation is a critical step in the post-exploitation phase of a cyber attack, where an attacker expands their control over the compromised system by gaining higher-level permissions, which is essential for executing commands that require administrative rights, accessing sensitive data, and ensuring the persistence of the attacker's presence within the system. It encompasses two primary types: vertical and horizontal. Vertical Privilege Escalation, or Privilege Elevation, involves elevating the attacker's current account permissions from a lower level to a higher level, often to an administrative or root account, aiming to gain more power and control over the system through exploiting vulnerabilities in the operating system, misconfigurations, or using stolen credentials that belong to a higher-privileged account. Conversely, Horizontal Privilege Escalation does not involve increasing the attacker's current level of permissions but rather entails moving laterally across accounts at the same permission level to access the data or functionalities specific to a different user account that the attacker does not originally control, possibly through guessing or cracking passwords, session hijacking, or exploiting flaws in application logic.
Lateral Movement: Lateral movement refers to the strategy used by attackers to navigate through a network after gaining initial access. Unlike privilege escalation, which focuses on elevating an attacker's permissions vertically (to higher levels of authority) or horizontally (across the same level of authority but to different user accounts), lateral movement is about spreading their foothold across multiple systems within the network. This step is essential for attackers seeking to identify and exploit valuable targets, extend their influence within the victim's environment, and maintain persistence. Techniques for lateral movement include using stolen credentials to access other machines, exploiting vulnerabilities in network protocols, and leveraging tools that enable remote control and execution of code on other hosts within the network. The goal is to increase the attacker's access and control over the network without necessarily increasing their privilege level on any single system.
Pivoting: Pivoting stands out from lateral movement and privilege escalation by specifically utilising a compromised system as a strategic base for attacking additional systems within the network, especially those not directly reachable from the attacker’s initial entry point. Unlike lateral movement, which involves spreading across multiple systems at the same network layer to extend the attacker's foothold, pivoting is a technique for deep network navigation. It enables the attacker to access isolated, segmented, or higher-security areas by "tunnelling" or "relaying" their actions through the initially compromised system. This method allows for the exploration and exploitation of parts of the network that are beyond direct access due to network segmentation or stricter security measures. In contrast to privilege escalation, which is focused on increasing the attacker's permission level within the network, pivoting is about leveraging the current position to penetrate deeper into network segments or to bypass security controls, without necessarily changing the attacker’s privilege level on any system. Pivoting is essential for accessing restricted network areas, exploring deeper network layers, and maximising attack impact by reaching sensitive or strategically important systems.
Persistence: Ensuring continued access to a compromised system, even after reboots or security updates. Techniques for persistence might include creating new accounts, modifying existing ones, or installing malware that automatically starts.
Exfiltration: The act of stealing data from the compromised system. Exfiltration can be as simple as copying files to a remote server or as complex as encrypting data for stealthy removal.
C2 (Command and Control) Communications: Refers to the communication between compromised systems and the attacker's infrastructure. C2 channels are used to control malware, exfiltrate data, and issue commands to compromised systems.
Beacon: A type of malware communication method used in post-exploitation to signal back to the attacker's command and control (C2) servers. Beacons typically operate at predetermined intervals, sending back information about the compromised system's status or receiving instructions for further actions. This low-and-slow approach helps evade detection by blending in with normal network traffic.
Implant: Refers to malware or any malicious code that is placed on a compromised system during the post-exploitation phase. Implants are designed to establish persistence, facilitate deeper network penetration, or gather sensitive information. Unlike beacons, which primarily communicate with C2 servers, implants can perform a wide range of functions, including opening backdoors, capturing keystrokes, or downloading additional payloads.
Credential Dumping: Extracting account information, like usernames and passwords, from a system. These credentials can be used for lateral movement or to access other systems and resources.
Defence Evasion: Techniques used to avoid detection by security software and analysts. This can include disabling security tools, modifying system logs, or using encryption to hide malicious activities.
If you don't know, now you know
Post-exploitation is a critical phase in the cybersecurity attack lifecycle, highlighting the actions attackers take after gaining initial access. Understanding the concepts and jargon of post-exploitation is crucial for both attackers in simulating realistic threats and defenders in securing systems against sophisticated attacks. For ethical hackers and penetration testers, knowledge of post-exploitation techniques helps assess the security posture of systems and networks.
By simulating attacker actions after gaining access, they can identify vulnerabilities in the post-exploitation phase and recommend mitigations to prevent real attacks. For cybersecurity professionals, understanding post-exploitation is essential for defending against advanced threats. It is not enough to stop initial access attempts; defenders must also be prepared to detect and respond to post-exploitation activities.
This involves monitoring for unusual behaviour, auditing system and network logs, and implementing strict access controls. As cybersecurity threats continue to evolve, so will the strategies and techniques used in post-exploitation, making ongoing education and vigilance essential to any security strategy.