The installation phase of the cyber kill chain marks a crucial turning point in an attack. After the successful exploitation of a vulnerability, the attacker’s goal shifts toward establishing a persistent presence on the victim’s system. During this phase, malicious code is installed to maintain access, often silently, enabling the attacker to proceed with further actions such as command and control, data exfiltration, or lateral movement. Understanding this phase is essential in cybersecurity because it represents the stage where temporary access becomes long-term compromise.

Installation techniques vary depending on the sophistication of the threat actor, the target environment, and the nature of the payload. In most modern cyberattacks, installation involves placing malware, backdoors, remote access tools (RATs), or trojans onto the compromised machine. The malware is designed to evade detection, remain persistent across reboots, and potentially update itself or fetch additional components from a command-and-control server. This step enables attackers to solidify their position inside a network and operate with greater stealth and control.

One of the most common forms of malware installed during this phase is a remote access trojan (RAT). RATs allow threat actors to control the victim system remotely, often with full administrative privileges. Tools like njRAT, DarkComet, and QuasarRAT have been widely used in targeted attacks. These tools can log keystrokes, capture screenshots, activate webcams, and download or upload files. While some of these RATs are publicly available and marketed for legitimate purposes, they are frequently weaponized by cybercriminals and used in both criminal and state-sponsored campaigns.

Advanced persistent threats (APTs) often employ sophisticated tools like Cobalt Strike or custom malware frameworks such as PlugX, Gh0st RAT, or Mimikatz. Cobalt Strike is especially popular for its modular approach. It allows the deployment of Beacon, a payload that can establish persistence, conduct privilege escalation, and maintain encrypted communications with the attacker’s infrastructure. In the installation phase, Cobalt Strike is used to deploy malware that can hide in memory, use signed binaries to avoid detection, or utilize living-off-the-land binaries (LOLBins) to blend in with normal system activity.

Persistence mechanisms are a vital part of installation. Threat actors use techniques like modifying registry keys, creating scheduled tasks, installing services, or leveraging Windows Management Instrumentation (WMI) to ensure their malicious code survives reboots and remains active over time. On Linux systems, attackers might add entries to crontab, modify systemd service files, or install rootkits. These persistence strategies allow attackers to maintain access even if initial infection vectors are identified and removed.

A real-world example of the installation phase is the infamous Stuxnet worm. Once Stuxnet exploited the target’s vulnerabilities, it installed highly customized payloads designed to manipulate industrial control systems (ICS). The installation included multiple drivers signed with stolen digital certificates to evade antivirus detection and ensured persistence on infected systems. Stuxnet’s level of stealth and its multi-layered installation process highlighted how state-sponsored actors can develop complex malware capable of long-term residence within highly secure environments.

Another notable case is the NotPetya attack in 2017. While initially believed to be ransomware, NotPetya’s goal was destruction rather than financial gain. After exploiting vulnerabilities and using stolen credentials to move laterally, the malware installed itself in a way that mimicked legitimate processes. Its installation included wiping key system components, ensuring that infected machines were rendered unusable. This attack demonstrated how installation can be used not just for persistence but also for sabotage.

Cybersecurity defenses against the installation phase include endpoint protection platforms (EPP), endpoint detection and response (EDR) solutions, and behavioral analysis tools. These technologies monitor for abnormal activities such as new service installations, registry changes, and unauthorized system modifications. EDR solutions, for example, can detect when a process attempts to persist after a reboot or uses suspicious techniques to hide its presence.

Application whitelisting and system hardening can also reduce the attack surface during the installation phase. By allowing only approved software to run and reducing unnecessary privileges, organizations can limit the ability of attackers to successfully install malicious code. Regular audits and integrity checks on critical system files help detect unauthorized changes that may indicate malware installation.

Security awareness training is another layer of defense. In many attacks, installation begins with user interaction, such as enabling macros in malicious Office documents or running unknown executables. Educating users about social engineering tactics and suspicious behavior can prevent attackers from gaining the initial foothold required to install their payloads.

In summary, the installation phase of the kill chain is where threat actors move from temporary access to entrenched presence. By installing malware, establishing persistence, and hiding their activity, attackers prepare the environment for the next stages of the attack lifecycle. Tools like Cobalt Strike, njRAT, and Mimikatz are commonly used in this phase to ensure control and stealth. Real-world incidents like Stuxnet and NotPetya highlight the critical nature of installation in advanced cyber threats. Preventing successful installation is one of the most effective ways to disrupt the kill chain and defend against long-term compromise in cybersecurity.