Penetration testing: Definition, types, steps, and key insights

Cyber threats don’t always make themselves known in obvious ways. Sometimes the biggest risks to your organization's security come from unnoticed gaps — a misconfigured firewall, an outdated plugin, or a forgotten user account. That's where penetration testing comes in.

Whether you're exploring such a service for the first time or comparing manual and automated testing approaches, this article will cover what penetration testing is, how it works, the different forms it can take, and why it's a vital part of any security strategy.

What is penetration testing (pentesting)?

Penetration testing (pentesting) is a controlled simulation of a cyberattack designed to spot security weaknesses before real attackers can exploit them. Security experts — often called ethical hackers — use the same techniques as malicious actors to test how well a system, network, or application resists the attacks.

For enterprise security, pentesting is critical because it helps identify potential vulnerabilities early. Unlike a real attack, a penetration test is planned beforehand to avoid causing any disruptions during the process. The goal is to identify vulnerabilities, understand how far an attacker could get if they tried to enter the system, and recommend fixes.

Pros of penetration testing

When done regularly and strategically, penetration testing offers several key benefits that go beyond surface-level assessments. By mimicking real-world attack scenarios, it:

• Finds real-world vulnerabilities. Pentests uncover critical security vulnerabilities that typical scans may miss, such as broken authentication flows or logic flaws.
• Tests detection and response capabilities. Pentesting shows how well a company's security features hold up during an active breach and how fast the team reacts.
• Supports compliance efforts. Pentesting helps organizations meet compliance standards that require regular assessments of system defenses and sensitive data protection.
• Reduces long-term risk. Proactive testing can prevent costly incidents by addressing vulnerabilities before attackers exploit them.

Cons of penetration testing

While a powerful security tool, pentesting is not without limitations. From costs to scope constraints, some challenges may impact how and when organizations choose to run tests:

• Only reflects a moment in time. A penetration test captures the state of a target system at one point. Without follow-up, new issues may go unnoticed.
• Qualified specialists are in short supply. Skilled penetration testers are in high demand, and working with a top pentest company can come with a high price tag.
• Potential for disruption. If not scoped carefully, testing against production systems may slow down services or trigger alerts unnecessarily.
• May not cover all threats. Some advanced or long-term threats, such as persistent social engineering pentest tactics, may fall outside the test's scope.
• Budget constraints. Pentesting cost can deter smaller businesses — even though the investment typically outweighs the cost of an actual breach.

Types of penetration tests

Penetration tests can target different layers of a company's infrastructure, depending on its risk profile, systems in use, and compliance needs. Each type of test focuses on a specific environment, simulating real-world attack vectors to spot security weaknesses. Below are the most common types of penetration testing, tailored to specific environments and threat scenarios.

• Network penetration testing identifies vulnerabilities in internal or external network infrastructure, including misconfigured firewalls, open ports, or outdated systems.
• Web application penetration testing evaluates websites and online platforms for issues like broken authentication, insecure inputs, and session mismanagement. Such type is crucial for any business handling user data via online services and is frequently offered by pentest service providers.
• Mobile application penetration testing monitors iOS and Android apps for improper data storage, weak encryption, and unsafe third-party libraries. It ensures sensitive data on user devices is protected from exposure.
• Cloud penetration testing assesses cloud-hosted environments (e.g., AWS, Azure) for misconfigured settings or overly permissive access, helping companies meet compliance and improve their cloud security posture.
• Wireless penetration testing analyzes Wi-Fi networks for threats such as rogue access points, weak encryption protocols, or unauthorized devices within range. It is used to secure on-premise connectivity.
• Social engineering penetration testing simulates phishing attacks, phone-based pretexting, or impersonation to test how easily users might unintentionally give away credentials or grant access — highlighting the human layer of risk.
• Physical penetration testing challenges the effectiveness of physical security systems like access badges, locked areas, or surveillance. It offers a full view of on-site security weaknesses that could allow unauthorized entry.
• External network penetration testing focuses on internet-facing assets like web servers, email gateways, or VPNs. It replicates how a remote attacker might attempt to gain access from outside the organization's network perimeter.
• Internal penetration testing simulates threats originating from within the organization, such as a disgruntled employee or a compromised endpoint. It helps assess how well security features protect internal systems once an attacker has already bypassed the perimeter.
• Application penetration testing analyzes how custom or third-party software handles input validation, access controls, and error conditions. It identifies flaws that may not surface in broader network or infrastructure assessments.

Many companies hire outside experts to tackle these tests, whether once or regularly, to keep their security strong. Usually these experts mix different test types to fit the company's needs and make sure they stay secure long term.

How does penetration testing work?

Penetration testing works by simulating real-world attacks on a system to identify and exploit security weaknesses before malicious actors can. The process involves several stages, from planning and reconnaissance to exploitation and reporting.

Throughout testing, specialized pentesting tools are used to scan and probe the target system's defenses. These tools help testers analyze network traffic, find vulnerabilities, and verify whether security features effectively prevent unauthorized access. The overall goal is to provide actionable insights that help security teams improve the system's defenses.

Stages of pentesting

The penetration testing process is typically divided into five key stages that guide testers from initial information gathering to final reporting.

1. Planning and reconnaissance

In this phase, testers define the scope and goals of the test and collect information about the target system. This process includes identifying potential entry points and gathering data on network infrastructure, web applications, and security features.

2. Scanning

Testers use automated and manual penetration testing tools to analyze the target system for vulnerabilities. This step involves examining how the system responds to various probes, scanning open ports, and assessing network traffic.

3. Gaining access

At this stage, testers attempt to exploit identified vulnerabilities to gain unauthorized access to the target system or sensitive data. This simulates real-world attack methods to evaluate the system's resilience.

4. Maintaining access

After gaining entry, testers try to maintain control within the system to assess how long an attacker could remain undetected. Generally, this phase helps reveal weaknesses in internal security controls.

5. Analysis and reporting

The final stage involves preparing a detailed penetration testing report that outlines the vulnerabilities found, exploitation methods used, and recommended remediation steps. Such a report helps security teams to strengthen their defenses.

Access levels for pentesters

Access levels define how much information pentesters have about the target system before starting their work. The type of access and information provided impacts their approach, the depth of testing, and the types of vulnerabilities they can uncover.

Opaque box

In the opaque box scenario, testers begin with no prior knowledge of the system — only what is publicly available or discoverable from outside. It simulates a real external attacker who has no inside help.

Pentesters rely on tools and creative techniques to map the target and find weaknesses, such as open ports, exposed services, or security flaws visible from the outside. While this method effectively tests perimeter defenses and external network security, it can miss vulnerabilities hidden deeper in the system or within internal processes.

Semi-opaque box

In the semi-opaque box scenario, testers receive limited information, such as user credentials, network diagrams, or system architecture overviews. This data gives them partial insight into the environment, allowing a more targeted and efficient testing process. With some knowledge of the system's layout, testers can combine external attacks with internal probing, focusing on areas likely to be vulnerable.

This approach often mimics the position of an insider or a user with limited access and helps uncover security weaknesses that a purely external test might overlook. It also aligns well with many penetration testing services aiming to balance depth and cost.

Transparent box

With the transparent box access level, testers get full access to all system details, including source code, configurations, and network maps. This deep level of access enables a thorough security assessment that can find hidden vulnerabilities in software, infrastructure, and processes.

Testers can review code for security flaws, check access controls, and examine how data flows within the system. Transparent box testing is ideal when organizations want a complete picture of their security posture or prepare for high-stakes audits and compliance checks. It requires advanced skills and specialized tools but offers the most comprehensive results.

What happens after a pentest?

After penetration testing is complete, the testers provide a detailed report summarizing their findings. The report outlines identified vulnerabilities, exploited weaknesses, and the potential impact on the system. It also includes recommendations for remediation to strengthen security.

Organizations use this report to prioritize fixes and improve their security posture. Additionally, pentests often trigger follow-up actions such as retesting, patch deployment, and updates to security policies or procedures. Effective communication between penetration testers and security teams is essential to ensure vulnerabilities are addressed and systems remain protected.

Penetration testing as a service (PTaaS)

Penetration testing as a service (PTaaS) is a model where organizations outsource their penetration testing needs to specialized providers who deliver ongoing testing and reporting via cloud platforms. This service uses both manual checks and automated tools to keep the computer system's security under constant watch.

PTaaS offers several benefits — it provides real-time insights, allows faster identification of security weaknesses, and offers flexibility in testing frequency. Companies can access expert penetration testers without building an in-house team, making it cost-effective for many businesses.

However, PTaaS also has drawbacks. It might not be as customizable as fully manual tests. Moreover, some sensitive setups may need tighter control than what cloud platforms can offer. Additionally, the quality of PTaaS depends heavily on the vendor's expertise and responsiveness.

Manual pentesting vs. automated testing

Manual penetration testing involves security experts = exploring a system to identify vulnerabilities using their knowledge, experience, and creativity. Such an approach allows for a deeper investigation of complex security weaknesses and can uncover issues that automated tools might miss.

Automated testing relies on software tools that scan systems for known vulnerabilities and common security flaws. These tools work faster and can check more targets regularly, but they might miss some hidden problems or give false alarms.

While automated pentest tools provide efficiency and scale, manual pentesting remains essential for uncovering nuanced vulnerabilities and understanding the overall security posture. Many companies use a combination of both methods to balance accuracy and speed in their penetration testing process.

Penetration testing vs. vulnerability scanning

Penetration testing and vulnerability scanning both aim to improve security but differ in scope and depth. Vulnerability scanning uses automated tools to identify known security flaws across systems, providing a broad overview of potential risks.

Pentesting goes further by exploiting vulnerabilities to assess their impact, simulating real-world attacks. This hands-on approach reveals how security weaknesses can be combined to gain unauthorized access or cause damage.

While vulnerability scanning is useful for regular checks and compliance, pentesting offers a deeper understanding of security gaps and their practical consequences. Together, they form complementary parts of a strong security strategy.

Penetration testing as a profession

Penetration testing is a growing field driven by the rising demand for skilled specialists who can identify and address security weaknesses. Businesses struggle to find qualified testers who combine technical knowledge with problem-solving skills.

From a business perspective, investing in pentest talent helps protect sensitive data and maintain trust. Salaries for testers reflect this demand, with competitive pay making it an attractive profession for cybersecurity experts.

Becoming a penetration tester typically requires specialized training and certifications, such as pentest certification courses, to ensure practitioners follow industry standards and methodologies. While it can be challenging work, companies view penetration testers as critical assets in their security teams.

Why is it crucial to conduct penetration testing regularly?

Regular penetration testing is essential for maintaining a strong security system because it helps organizations identify and fix critical security vulnerabilities before attackers exploit them. Security threats continuously evolve, and ongoing testing ensures that defenses keep up with new risks.

Pentest helps sensitive data, computer systems, and network infrastructure. It complements other strategies like attack surface management and data breach monitoring, all crucial for keeping a company safe.

By prioritizing pentest services, businesses reduce their threat exposure and strengthen their overall security posture. This approach is vital for protecting company assets and maintaining customer trust in today's digital environment.