Penetration Testing definition
Penetration testing is an authorized, simulated cyberattack on a system, application or network, performed by security professionals to find exploitable vulnerabilities before real attackers do. Testers use the same techniques as attackers, within an agreed scope and rules, and deliver a report describing confirmed weaknesses, their business impact and how to fix them.
Types of penetration testing
Penetration tests are scoped to a specific target, because each type of system has different attack surfaces, tools and techniques. Organizations usually test their most exposed and most sensitive systems first, then rotate through the rest of their environment over time, retesting whenever major changes are released or new regulations apply.
- Web application testing: authentication, access control, injection and business logic flaws.
- API testing: authorization, data exposure and rate limiting.
- Mobile application testing: insecure storage, network traffic and backend APIs.
- Network testing: external and internal infrastructure, services and segmentation.
- Cloud configuration testing: identity, storage and network settings in AWS, Azure or GCP.
- Social engineering: phishing and physical access tests.
The penetration testing process
A test begins with scoping and rules of engagement: which systems are included, which techniques are allowed, testing windows and emergency contacts. Testers then gather information about the target, map its attack surface, and identify potential vulnerabilities with a mix of automated tools, such as Burp Suite or Nmap, and manual analysis. Manual work is essential, because many serious flaws, especially in business logic and access control, are invisible to scanners.
Next, testers attempt to exploit findings to confirm they are real and to measure impact, for example by accessing another customer's data. They document each issue with evidence, a risk rating and remediation guidance. After fixes, a retest verifies that vulnerabilities are closed. Findings that cannot be fixed immediately should get compensating controls and a tracked deadline.
Black box, grey box and white box testing
In black box testing, testers start with no internal knowledge, like an external attacker. Grey box testing provides limited information, such as user accounts with different roles, which is the most common approach for web applications because it tests realistic authorization scenarios efficiently. White box testing gives full access to source code, architecture and documentation, allowing the deepest coverage in the available time. The right choice depends on goals, budget and the threats you are most concerned about.
How often should you run penetration tests?
Many organizations test critical applications at least annually and after significant changes, such as new features handling payments or personal data, major architecture changes or cloud migrations. Standards and customer requirements, including PCI DSS and many enterprise vendor assessments, expect regular testing. Fast-moving teams increasingly supplement periodic tests with continuous scanning, bug bounty programs and security testing in their CI/CD pipelines, so issues are caught between formal tests. Testing staging environments that mirror production keeps risk to live users low.
What a good penetration test report includes
A useful report has an executive summary in business terms, a clear scope statement, and findings ranked by risk, each with reproduction steps, evidence and specific remediation advice. It separates confirmed exploits from informational observations instead of padding the report with scanner output. Nexzem's penetration testers deliver reports written for both leadership and developers, followed by a retest once fixes are in place.