What Is Penetration Testing? Pen Testing Types, Process & Benefits

Penetration testing — often called pen testing or ethical hacking — is an authorized, simulated cyber attack designed to identify exploitable security weaknesses before real attackers find them. This guide covers what penetration testing actually is, the different types and methodologies, what a good engagement looks like end-to-end, the deliverables you should expect, and how to evaluate providers.

What is penetration testing?

Penetration testing — pen testing for short — is the authorized practice of attempting to gain unauthorized access to an organization's systems, applications, networks or facilities using the same techniques a real attacker would. The goal is to identify exploitable weaknesses, demonstrate impact and provide an actionable remediation plan. Pen testing is performed by ethical hackers under a written contract that defines scope, rules of engagement and disclosure obligations.

Penetration testing vs vulnerability assessment vs red team

• Vulnerability assessment — automated, broad, scanner-driven. Output: a list of potential issues.
• Penetration test — human-led, narrow, validates impact. Output: a prioritized list of exploitable issues.
• Red team — adversary simulation across the whole org. Output: an answer to "would we notice?".

The 5 main types of penetration testing

1. Network penetration testing

External and internal. Tests perimeter and internal network segments — exposed services, misconfigured firewalls, default credentials, vulnerable services and lateral movement paths.

2. Web application penetration testing

OWASP-aligned testing of websites, web apps and APIs. Covers authentication, authorization, business logic, input validation and the API surface. See our deep dive on web pentesting.

3. Mobile application penetration testing

iOS and Android. Tests local data storage, IPC, certificate pinning, client-side logic and the mobile-specific API surface. Aligned with OWASP MASVS.

4. Cloud penetration testing

AWS, Azure and GCP. Tests IAM misconfiguration, exposed storage, metadata service abuse, container escape and lateral movement across accounts. Each cloud provider has its own rules of engagement.

5. Social engineering and physical

Phishing, vishing, smishing, USB drops and physical intrusion. Tests the human and physical layers that technical tests miss entirely.

Black-box, grey-box and white-box

These describe the information given to the tester. Black-box: nothing but the target. Grey-box: limited credentials and architecture overview. White-box: full source, credentials and documentation. Grey-box is the default for most engagements; white-box for first-time tests of critical systems; black-box for periodic adversary-simulation cycles.

Pen testing methodologies

• PTES — Penetration Testing Execution Standard. End-to-end engagement structure.
• OWASP WSTG — Web Security Testing Guide. The reference for web app testing.
• OWASP MASVS / MSTG — mobile app verification and testing standards.
• OSSTMM — Open Source Security Testing Methodology Manual. Network-focused.
• NIST SP 800-115 — federal guidance on technical security testing.

The 5 phases of a pen test engagement

1. Scoping and rules of engagement

Define targets, allowed techniques, attack windows, escalation paths and contractual constraints. Get written authorization.

2. Reconnaissance

Passive (OSINT) and active (scanning, enumeration) information gathering.

3. Exploitation and post-exploitation

Validate vulnerabilities with working proofs of concept; demonstrate impact through lateral movement, privilege escalation and access to sensitive data — within scope.

4. Reporting

Executive summary, technical findings with reproduction steps, evidence, business impact, remediation guidance and references.

5. Retest

After fixes, re-verify each finding and reissue the report with status. No retest = incomplete engagement.

Why penetration testing matters

• Validates that controls work in practice, not just on paper.
• Required by PCI DSS, ISO 27001, SOC 2, HIPAA and most cyber insurance carriers.
• Surfaces business logic and chained-vulnerability issues scanners cannot find.
• Generates the evidence sales teams need to close enterprise deals.
• Builds the muscle of "think like an attacker" inside engineering.

How much does penetration testing cost?

European market ranges in 2026: a focused web app pentest €8K–€20K; external network €5K–€15K; mobile app €10K–€18K; cloud account audit €15K–€30K; full multi-target engagement for a mid-sized SaaS €40K–€80K. Price varies with scope, tester seniority and report quality. Cheap pen tests usually mean automated scans rebranded — ask to see a sample report before signing.