What is penetration testing?

Penetration testing (often called pentesting) is a controlled cybersecurity assessment in which authorized security professionals simulate real-world attacks against a system, network, application, or organization to identify vulnerabilities before malicious attackers can exploit them.

Understanding penetration testing

Penetration testing, unlike malicious hacking, is performed ethically and with permission, with the goal of finding vulnerabilities before real attackers do. According to CISA, a pen test “can be conducted from an external and/or internal view.”

A penetration test works by actively attempting to exploit vulnerabilities in a safe and structured way to determine how much real-world damage could occur if those weaknesses were targeted.

It aims to answer three critical questions:

• What vulnerabilities exist in the system?
• Can those vulnerabilities actually be exploited?
• What is the potential impact if they are exploited?

How penetration testing works

According to IBM, penetration testing follows a structured process designed to mimic the tactics, techniques, and procedures used by real-world attackers. The steps are as follows:

Pre-testing stage

Before a pen test is conducted, “the testing team and the company set a scope for the test.” The scope defines the systems to be tested, specifies the testing schedule, and outlines the methods available for penetration testers. “The scope also determines how much information the pen testers will have ahead of time:

• In a black-box test, pen testers have no information about the target system. They must rely on their own research to develop an attack plan, as a real-world hacker would.
• In a white-box test, pen testers have total transparency into the target system. The company shares details like network diagrams, source codes, credentials, and more.
• In a gray-box test, pen testers get some information but not much. For example, the company might share IP ranges for network devices, but the pen testers have to probe those IP ranges for vulnerabilities on their own.”

Once the scope has been determined, the tester chooses a pen test method. “Common ones include OWASP's application security testing guidelines, the Penetration Testing Execution Standard (PTES), and the National Institute of Standards and Technology (NIST) SP 800-115.”

The procedure often follows the same general steps regardless of the pen test method a testing team chooses.

Reconnaissance

During this stage, the “testing team gathers information on the target system.” To do this, the testers “use different recon methods depending on the target.”

Reconnaissance may include identifying domain names, IP addresses, network architecture, technologies in use, and publicly available information that could help an attacker gain access. The information gathered helps testers understand potential attack surfaces and develop a strategy for the assessment.

Scanning and vulnerability discovery

In this step, penetration testers use the information gathered during the reconnaissance phase to identify vulnerabilities in the system that can be exploited. They use a combination of automated tools and manual techniques to scan systems for weaknesses.

This stage focuses on identifying vulnerabilities such as outdated software, misconfigured systems, weak authentication mechanisms, exposed services, and application security flaws.

Exploitation

After identifying potential vulnerabilities, testers attempt to exploit them in a controlled manner. Common attacks include SQL injections to extract sensitive data, cross-site scripting to embed malicious code, denial-of-service assaults to disrupt services by overwhelming them, social engineering tactics to deceive employees, brute force attempts to crack passwords, and man-in-the-middle attacks to intercept sensitive information.

Escalation

After successfully exploiting a vulnerability, penetration testers often attempt to move deeper into the environment to determine how far an attacker could progress after gaining an initial foothold. This process, sometimes referred to as vulnerability chaining, involves linking multiple vulnerabilities together to access additional systems, data, or resources. During this phase, testers also evaluate whether they can maintain access to the environment while escalating their privileges and avoiding detection by security controls. The objective is to simulate the behavior of sophisticated attackers, including advanced persistent threats (APTs), which are known for establishing long-term access within a network and moving laterally across systems over extended periods. This helps organizations understand the potential consequences of a breach and identify weaknesses in monitoring and incident detection capabilities.

Reporting and remediation

The final stage involves documenting the findings and providing recommendations for remediation. IBM notes that penetration testing reports typically include details about discovered vulnerabilities, evidence of successful exploitation, the potential business impact, and prioritized recommendations for addressing the identified risks. These reports provide organizations with a roadmap for strengthening their security posture and reducing the likelihood of future attacks.

By following this structured approach, penetration testing provides a realistic assessment of an organization's ability to withstand cyberattacks and helps security teams focus their efforts on the vulnerabilities that pose the greatest threat.

Types of penetration tests

While all penetration tests involve simulating a cyberattack, different tests focus on different parts of an organization's technology environment. According to IBM, penetration testing can take several forms depending on the assets being evaluated and the security risks an organization faces:

Application penetration testing

Application penetration tests focus on identifying vulnerabilities in software applications, including websites, web applications, mobile applications, cloud-based applications, Internet of Things (IoT) applications, and application programming interfaces (APIs). Testers search “for vulnerabilities that are listed in the Open Web Application Security Project (OWASP) Top 10. The OWASP Top 10 is a list of the most critical vulnerabilities in web applications. The list is periodically updated to reflect the changing cybersecurity landscape, but common vulnerabilities include malicious code injections, misconfigurations, and authentication failures. Beyond the OWASP Top 10, application pen tests also look for less common security flaws and vulnerabilities that may be unique to the app at hand.”

Network penetration testing

Network penetration testing evaluates the security of an organization's network infrastructure. IBM notes that these assessments are generally divided into two categories: external and internal testing. External tests simulate attacks originating outside the organization and focus on internet-facing assets such as servers, websites, routers, and employee devices. Internal tests simulate threats from malicious insiders or attackers who have already obtained valid credentials, helping organizations understand how far an attacker could move within the network if an initial compromise occurred.

Hardware penetration testing

Hardware penetration tests examine devices connected to the network, including laptops, mobile devices, IoT devices, and operational technology (OT). In a hardware penetration test, the tester looks for “software flaws, like an operating system exploit that allows hackers to gain remote access to an endpoint.” Additionally, they may look for “physical vulnerabilities, like an improperly secured data center that malicious actors might slip into.”

Personnel penetration testing

People are often considered one of the most significant cybersecurity risks, contributing to 95% of data breaches. Personnel penetration testing assesses employees' susceptibility to social engineering attacks. Testers may conduct phishing, voice phishing (vishing), or SMS phishing (smishing) exercises to determine whether employees can recognize and appropriately respond to malicious communications. These assessments may also include evaluations of physical security practices, such as attempts to gain unauthorized access to facilities through impersonation or tailgating techniques.

Read also: Different types of phishing and how to prevent them

Tips and best practices

To get the most value from penetration testing, organizations should treat it as an ongoing security practice rather than a one-time exercise.

• Test regularly: Conduct penetration tests periodically and after major system changes to identify new vulnerabilities.
• Define a clear scope: Establish which systems, applications, and networks will be tested before the engagement begins.
• Use a comprehensive approach: Assess networks, applications, cloud environments, endpoints, and, where appropriate, human factors through social engineering tests.
• Integrate testing into broader security efforts: Penetration testing should complement vulnerability management, employee training, and incident response planning.

See also: HIPAA Compliant Email: The Definitive Guide (2026 Update)

FAQS

How is penetration testing different from a vulnerability assessment?

A vulnerability assessment identifies potential security weaknesses, while a penetration test goes a step further by attempting to exploit those weaknesses to determine their real-world impact.

Who should conduct a penetration test?

Penetration tests should be performed by qualified cybersecurity professionals with the necessary expertise and authorization to test systems safely and ethically.

Does a successful penetration test mean a system is secure?

No. A penetration test provides a snapshot of security at a specific point in time. New vulnerabilities can emerge as systems change and threats evolve, which is why regular testing is important.