Penetration testing (or pen testing) is an authorized, simulated cyberattack designed to test the security of a production system.Ethical hackers perform penetration tests, emulating the behavior of cybercriminals to evaluate your softwares security and identify any weaknesses. During a pen test, these cybersecurity specialists use a range of techniques to attack a system. Once they have gained access, their goal is to demonstrate the potential damage that somebody could do during a real attack.Penetration testing is an effective way to identify and prioritize security flaws in your software, protecting both your organization and users from cyberattacks. See also: SAST vs DAST: Differences And When to UseWhy is penetration testing important?Cybercriminals typically seek to steal sensitive data, such as company IP, financial information, or users data, and/or disrupt operations. A successful cyberattack can result in serious reputational and financial damage (enough to jeopardize the future of your business) and may also expose you to liability and regulatory penalties.With cyberattacks becoming increasingly common, the importance of software security cannot be overstated. A penetration test provides a realistic assessment of how well your system will withstand a cyberattack and identifies weaknesses that you should address. Why penetration testing matters: risk vs. resilienceWithout penetration testingWith penetration testing Unknown vulnerabilities remain hidden in your code or infrastructure Known exploits are identified before attackers can abuse them High risk of data breaches, IP theft, or operational disruption Stronger defenses built around real attack simulations Financial losses from fines, lawsuits, or ransom demands Demonstrated compliance with ISO27001, HIPAA, and other standards Reputational damage after publicized incidents Customer trust reinforced through visible due diligence Delayed response to incidents you didnt anticipate Faster remediation guided by expert pen test reportsAn external penetration testing service will provide a detailed report of the attempted attacks, the exploits found, and the potential harm that could be inflicted.As a proven security testing technique, penetration testing is recommended by several security standards and regulations, including ISO27001 and HIPAA. Running regular pen tests (and acting on the findings) can be used to demonstrate due diligence and compliance with these standards.Black box, white box, and gray box penetration testingDepending on your goals, you can run penetration tests using a black box, white box, or gray box approach. The different approaches refer to the amount of information provided to the pen testers in advance of the exercise.Black box testingAlso known as opaque box or blind testing, this approach simulates an attack by an outsider. In a black box test, the pen testers are given only the name of the organization or product under test. Its then up to them to glean whatever information they can to mount an attack.To make the test even more realistic, you can run a double-blind pen test, in which employees of your organization are unaware that the test is happening.Gray box testingIn a semi-opaque or gray box test, pen testers are given some information in advance. This might include system diagrams or design documents, or potentially credentials for a part of the system or a related service. Taking a gray box approach simulates an attack following a leak of confidential information or the actions of a disgruntled employee.White box testingWith a transparent or white box approach, pen testers have access to all the source code, binaries, containers, and any other artifacts of the system. While not a realistic attack, a white box penetration test is the quickest way to conduct this type of test and can be useful if you want rapid feedback so you can address security flaws quickly. Once you have addressed any issues, you may want to follow up with a black box test to ensure nothing has been missed.Vulnerability scanning vs. penetration testingAn effective cybersecurity strategy should involve multiple levels of security testing. This includes both automated vulnerability scans, such as Static Application Security Testing (SAST) and Dynamic Application Security Testing (DAST), as well as manual techniques like pen testing.Vulnerability scanners check your source code or software systematically for known security flaws. Because they are reasonably quick to run and require no manual intervention, they are ideal for inclusion in your automated CI/CD pipeline. Vulnerability scanning vs. penetration testingAspectVulnerability scanningPenetration testingTypeAutomatedManualTechniquesSAST, DAST, predefined rule setsSimulated real-world attacks by ethical hackersScopeSource code, known vulnerabilitiesEntire system: code, infrastructure, social engineering, physical securityDetection abilityFast and repeatable; ideal for frequent useSlow; time-intensive due to human effortCostLow; can run in every CI/CD cycleHigh; typically done a few times a yearIdeal use caseContinuous feedback in CI/CD pipelineIn-depth analysis for high-risk releases or compliance needsLimitationsDoesnt test exploit feasibility or user behaviorNot scalable for every build; limited frequencyBest when combined withPenetration testing for real-world attack simulationAutomated scans for consistent baseline coverageThis ensures you get regular and rapid feedback on each set of code changes, allowing you to address any new security issues quickly and efficiently.On the other hand, automated security scans can only ever discover the issues theyve been programmed to detect. As a result, they cannot identify new vulnerabilities or combinations of exploits. The fully automated process also carries a higher risk of false positives. This is where pen testing can offer advantages.Penetration testing is a form of manual security testing that involves skilled individuals mounting realistic attacks on your system. In addition to checking for common vulnerabilities, pen testers often chain exploits together, leveraging each small weakness in the same way an attacker would to gain access to a system.Pen testers also look beyond the codebase, exploiting social engineering tactics and physical security gaps to compromise systems. As a result, penetration tests can reveal flaws in your defenses that might go unnoticed by automated security tests.The downside of pen tests is that they are expensive and time-consuming to run. How frequently you run penetration tests will depend on your risk profile and budget, but it is typically a few times a year or less.If youre releasing changes frequently, penetration testing alone is not enough to defend against cyberattacks. However, by combining pen testing with vulnerability scans and other automated security tests, you can leverage the benefits of each approach. Find out more about automated testing from our CI/CD guide.Types of penetration testingPen testing can involve a range of methods. Rather than focusing on a particular type to the exclusion of others, pen testers combine different methods according to the system under test and the organizations requirements.External vs. internalIn an external penetration test, the simulated attack starts from outside the organizations network. The initial target might be a router, external servers, employee computers, or cloud-hosted services. The pen tester aims to find a way in and then see what else they can access and what damage they can do.By contrast, an internal test starts from inside the network. You can use this to simulate an attack by a rogue employee or an attack that could follow a successful phishing attempt.Application testingApplication testing involves looking for vulnerabilities in deployed software, such as web apps, mobile apps, APIs, and IoT devices. Pen testers will look for common security flaws, such as SQL injection, broken authentication, and others listed in the OWASP Top 10.Although vulnerability scans can detect these types of issues, fixes are sometimes deprioritized if they are not considered a significant threat. However, minor exploits can be chained together by a creative pen tester to reveal a viable attack vector.Social engineeringSocial engineering targets the individuals working at an organization. Attack vectors include phishing emails and phone calls to extract valuable information and credentials, tailgating staff entering the building, or cloning office badges (often with the help of photos on social media) and masquerading as an employee or contractor.Physical securityPhysical security can involve searching for vulnerabilities in hardware, such as unpatched servers, or simply gaining entry to premises and then plugging a device into a network socket. Once a pen tester has gained access to the network in this way, they can seek to access key systems with the help of malware or key loggers, and then download or take screenshots of sensitive data.How to do penetration testingMost pen testers will follow a process that includes the following steps.Rules of engagementBefore starting, the pen testers should agree on a brief with the organization that defines the tests target and the rules of engagement. This should include what forms of testing are acceptable and what is off the table (such as phishing attempts on staff or forcing entry to premises), as well as the contact to inform of progress. The brief should also provide any additional context (in the case of a white or gray box test) and specify whether employees are aware that a pen test is being run.Planning and reconnaissanceBased on the brief, the pen testing team will collect as much information as possible about the software. This may include scouring public websites, published documentation, social media accounts, and public repositories to learn more about the software architecture and how its hosted. They will also gather intelligence about the organization and look for ways to get into the network so they can access key systems and data.Once the reconnaissance is complete, the pen testers identify potential attack vectors and prioritize them, while considering how to evade detection at all stages of the exercise.Gaining accessThe pen testing team then attempts to gain access to the system through any means allowed in the brief. During this stage, they may use various tools to automate specific elements of the process, including vulnerability scanners, credential cracking tools, port scanners, and network analyzers.If permitted by the rules of engagement, they may use social engineering techniques to gain access to premises and attempt to install malware on devices within the network so they can continue the attack remotely.Maintaining accessOnce inside, pen testers attempt to escalate privileges and access critical systems or demonstrate the potential to disrupt them.Remaining undetected throughout this process is crucial if somebody discovered a real hacker, they could avert the attack. The longer a pen tester can remain undetected, the higher the risk that an advanced persistent threat could be carried out.Covering tracksBefore concluding, pen testers remove all traces of their activity. This both tests the organizations ability to detect intrusions and ensures nothing remains for real attackers to exploit. This might involve removing any hardware or malware they have planted, and reverting any configurations to their original state.ReportingFinally, the pen testers will write a report detailing what they attempted, the defenses that worked, how they managed to gain access, and the damage they could have caused. They may provide evidence of how far they penetrated the defenses by placing a file in a secure location or taking a screenshot of sensitive data. They will also suggest recommendations on how you can enhance your security and prevent similar attacks in the future.Popular penetration testing toolsAlthough penetration testing is a form of manual security testing, pen testers typically use many tools to simulate an attack, just as a malicious actor would. By using these tools on your systems, you can also detect potential vulnerabilities and address them before theyre exploited.Reconnaissance toolsDuring the reconnaissance phase, pen testers may use network scanners, like Nmap, to scan IP addresses and ports to find out more about the system design and identify potential entry points. Network packet analyzers, such as Wireshark, are used to gain a deeper understanding of the systems in use and look for sensitive data or credentials being transmitted without encryption.Credential crackingTools designed to crack encryption protocols or mount brute force attacks, such as Hydra and John the Ripper, are frequently used to try to gain access to systems. Other options include installing key loggers on employees devices or using phishing emails to trick users into divulging their credentials.Exploitation toolsTools such as Metasploit, Burp Suite, and OWASP ZAP enable pen testers to automate common attacks including SQL injection, cross-site scripting, and fuzzing. Having identified a vulnerability, pen testers may then chain several exploits together to mount a more sophisticated attack.Business perspective: the ROI of penetration testingPenetration testing is often seen as a technical requirement, but it can also be viewed as a business safeguard. A successful cyberattack can lead to downtime, reputational damage, regulatory fines, or loss of sensitive data. In some cases, the financial impact may exceed the cost of a structured penetration testing program.While vulnerability scans are useful for identifying known issues, penetration testing simulates how an attacker might exploit multiple weaknesses in combination. This type of testing can uncover risks that are difficult to detect through automation alone.For organizations operating in regulated industries, penetration testing may also support compliance with standards such as ISO27001, HIPAA, and PCI DSS. In this context, it can be used to demonstrate due diligence and reduce legal exposure.When penetration testing pays for itselfAlthough penetration tests can be expensive to run, they are often justified in scenarios with elevated risk. These include:Launching a new product or major architectural changeStoring or processing sensitive information, such as personal data or payment detailsPreparing for a security certification or compliance auditFollowing a publicized security incident affecting a competitor or similar companyExpanding into new infrastructure environments, such as third-party APIs or cloud servicesIn such cases, the cost of remediation after a breach may significantly outweigh the cost of identifying and fixing issues earlier through targeted testing.Combining pen testing with automated security scanningPenetration testing offers detailed insight into your security posture, but it is not designed for continuous use. To maintain security at scale, its best used in combination with automated tools.For example, vulnerability scanners can be integrated into your CI/CD pipeline to provide regular feedback on source code and deployed software. This allows you to identify common issues quickly, without the need for manual intervention.Read also: What Is a CI/CD Pipeline?Pen testers, on the other hand, can focus on exploring complex attack paths, misconfigurations, or issues that are specific to your architecture. This combination ensures broader coverage while making efficient use of internal or third-party security resources.Tools such as OWASP ZAP or Snyk can be added to your build process, while platforms like TeamCity allow you to automate scanning tasks and generate reports at each deployment stage.Setting up TeamCity Snyk plugin