What Is Penetration Testing? Types, Process and Best Practices
Every organization has vulnerabilities. The real question is whether you find them first or an attacker does. Penetration testing answers that question by putting your systems under controlled, authorized attack, so you can see what a real adversary could reach and fix it before it matters.
This guide explains what penetration testing is, how it differs from vulnerability scanning and red teaming, the main types of penetration tests, how a typical engagement runs from scoping to retest, which standards professional testers follow and what to look for when choosing a provider.
What Is Penetration Testing?
Penetration testing (often shortened to pentest) is an authorized, simulated attack against a system, application or network, carried out to find and safely exploit security weaknesses. A penetration tester uses the same techniques as a real attacker, but within an agreed scope, with written permission and with the goal of helping the organization fix what they find.
The key word is exploit. A penetration test does not stop at listing potential issues. It proves which weaknesses are actually exploitable, shows how they can be chained together and demonstrates their business impact: which data could be read, which accounts could be taken over, which systems could be reached.
A penetration test typically answers questions such as:
- Can an outsider get into our network or application?
- Can a regular user access another customer’s data or gain administrator rights?
- If an attacker compromises one laptop, how far can they move inside the network?
- Do our security controls and monitoring actually detect and stop an attack?
Penetration Testing vs. Vulnerability Scanning
The two are often confused, but they answer different questions. A vulnerability scan is automated and broad; a penetration test is manual, deep and focused on real-world impact.
Vulnerability scanning | Penetration testing | |
|---|---|---|
How it works | Automated tools compare systems against known vulnerability signatures | Skilled testers combine tools with manual analysis and exploitation |
What it finds | Known vulnerabilities and missing patches | Exploitable weaknesses, chained attack paths, business logic flaws |
False positives | Common | Findings are verified by exploitation |
Business logic and authorization flaws | Rarely detected | A core focus |
Typical frequency | Weekly or monthly | Annually and after significant changes |
Output | List of potential issues | Evidence-based report with impact and remediation |
The two complement each other. Regular scanning keeps known issues under control between tests; penetration testing finds what scanners cannot. For a deeper comparison, see our guide to vulnerability assessment vs penetration testing.
Penetration Testing vs. Red Teaming
A penetration test tries to find as many exploitable weaknesses as possible within a defined scope and time frame. A red team engagement has a different goal: it simulates a specific, realistic adversary trying to reach a defined objective, such as access to payment systems, while staying undetected for as long as possible. Red teaming tests not only your vulnerabilities but also your detection and response capabilities. Most organizations start with penetration testing and move to red team exercises as their security program matures.
Why Penetration Testing Matters
Security tools, policies and architecture diagrams describe how an environment should behave. A penetration test shows how it actually behaves under attack. The main benefits are:
- Find exploitable weaknesses before attackers do. Testers uncover issues such as broken access control, exposed services, weak credentials and misconfigurations, and prove which ones lead to real compromise.
- Understand business impact, not just technical findings. A good test explains what an attacker could achieve: customer data exposure, financial fraud, ransomware deployment or service disruption.
- Prioritize remediation. With hundreds of scanner findings, teams need to know which handful truly matter. Exploited, evidence-backed findings make prioritization straightforward.
- Validate security investments. A test shows whether your firewall rules, endpoint protection, segmentation and monitoring work as intended.
- Meet compliance and customer requirements. Standards and frameworks such as PCI DSS, ISO/IEC 27001 and SOC 2 expect regular security testing, and enterprise customers increasingly ask for recent penetration test results during vendor reviews.
- Reduce the cost of incidents. Fixing a vulnerability found in a test costs far less than responding to a breach, notifying regulators and customers, and recovering lost trust.
Types of Penetration Testing
Penetration tests are defined by the target. Most organizations need a combination of the types below, depending on what they build and run. You can find an overview of all our penetration testing services on our Offensive Security page.
External Penetration Testing
External testing targets everything reachable from the internet: public IP ranges, VPN gateways, email and DNS services, remote access portals and exposed management interfaces. The question it answers is simple: can an outside attacker get in? See External Penetration Testing.
Internal Network Penetration Testing
Internal testing assumes an attacker already has a foothold, for example through a phishing email or a compromised laptop. Testers look for weak internal services, credential exposure, Active Directory misconfigurations and paths to domain administrator. See Internal Network Penetration Testing.
Web Application Penetration Testing
Web application testing covers authentication, session management, access control, input handling and business logic, typically following the OWASP Web Security Testing Guide. Authorization flaws, where one user can access another user’s data, are among the most common and most damaging findings. See Web Application Penetration Testing.
API Penetration Testing
APIs power mobile apps, single-page applications and partner integrations, and they expose business logic directly. API testing focuses on the OWASP API Security Top 10, including broken object level authorization, mass assignment and token weaknesses, for both REST and GraphQL. See API Security Testing.
Mobile Application Penetration Testing
Mobile testing examines iOS and Android applications and their back-end APIs: insecure local data storage, weak certificate validation, hardcoded secrets, reverse engineering risks and flaws in authentication flows, following the OWASP MASTG. See Mobile Application Penetration Testing.
Cloud Penetration Testing
Cloud testing targets AWS, Azure and Google Cloud environments, where most serious issues come from identity and configuration rather than software bugs: over-privileged IAM roles, public storage buckets, exposed secrets and privilege escalation paths across accounts. See Cloud Penetration Testing.
Kubernetes and Container Penetration Testing
Container platforms introduce their own attack surface: over-privileged service accounts, privileged containers, missing network policies and weak admission control. Testing shows whether a compromised workload can take over the cluster. See Kubernetes Penetration Testing.
Wireless Penetration Testing
Wireless testing assesses Wi-Fi encryption and authentication, guest network isolation and the risk of rogue access points that could give an attacker a way into the internal network from the parking lot. See Wireless Network Testing.
Social Engineering Testing
People are often the easiest way in. Social engineering tests use controlled phishing campaigns, phone-based pretexting and sometimes physical access attempts to measure how employees respond and how quickly incidents are reported. See Social Engineering Testing.
AI and LLM Application Testing
Applications built on large language models face new risks such as prompt injection, sensitive data leakage and agents that can be manipulated into misusing their tools. Testing follows the OWASP Top 10 for LLM Applications. See AI & LLM Security Testing.
Software Supply Chain Testing
Modern software depends on CI/CD pipelines, package registries and third-party components. Supply chain testing looks for ways an attacker could tamper with builds, steal pipeline secrets or inject malicious dependencies. Our analysis of the supply chain attack on Trivy, KICS and LiteLLM shows why this matters. See Software Supply Chain Penetration Testing.
Black Box, Gray Box and White Box Testing
Besides the target, a penetration test is defined by how much information the testers receive in advance.
Approach | What testers know | Simulates | Strength | Limitation |
|---|---|---|---|---|
Black box | Only the target name or URL | An external attacker with no inside knowledge | Realistic outside view | Time spent on discovery, lower coverage |
Gray box | User accounts, basic documentation | An attacker with some access, or a malicious user | Best balance of realism and coverage | Requires test accounts and preparation |
White box | Source code, architecture, credentials | A well-informed insider, or a deep review | Maximum coverage and depth | Less representative of an outside attacker |
For most web, API and mobile applications, gray box testing gives the best value: testers receive accounts for each user role, so they can spend their time testing authorization and business logic instead of guessing how the application works. White box testing, often combined with a secure code review, is the most thorough option for critical applications.
The Penetration Testing Process, Step by Step
Every provider has its own methodology, but professional engagements follow the same overall flow.
1. Scoping and Rules of Engagement
The engagement starts by agreeing on what will be tested and how: target systems and IP ranges, user roles, testing windows, out-of-scope systems, contacts for emergencies and how critical findings will be communicated. All of this is captured in a written authorization. Testing without it is not a penetration test; it is unauthorized access.
2. Reconnaissance
Testers gather information about the target: domains and subdomains, exposed services, technologies in use, employee information relevant to the scope, leaked credentials and public code repositories. Good reconnaissance often reveals forgotten assets that nobody knew were exposed.
3. Scanning and Enumeration
Using automated tools and manual techniques, testers map open ports, services, application endpoints and user roles, and identify potential vulnerabilities. This is where a vulnerability scan would end.
4. Exploitation
Testers attempt to exploit the identified weaknesses in a controlled way to confirm they are real and to measure their impact: bypassing authentication, accessing other users’ data, executing code or extracting sensitive information. Exploitation is done carefully to avoid disrupting production systems.
5. Post-Exploitation and Lateral Movement
Once initial access is achieved, testers examine how far an attacker could go: escalating privileges, moving to other systems, reaching sensitive data and testing whether segmentation and monitoring stop them. This step turns individual findings into a realistic attack path.
6. Reporting
Findings are documented with evidence, risk ratings, business impact and clear remediation guidance, alongside an executive summary for leadership. Critical issues are usually reported immediately during testing rather than waiting for the final report.
7. Remediation and Retest
The engagement is not finished when the report is delivered. After your team fixes the findings, testers verify the fixes and update the report. A retest confirms that vulnerabilities are actually closed and gives auditors and customers evidence of remediation.
Penetration Testing Methodologies and Standards
Professional testers do not improvise. They follow recognized methodologies so that tests are consistent, repeatable and comparable over time:
- PTES (Penetration Testing Execution Standard): defines the phases of an engagement, from pre-engagement interactions to reporting.
- NIST SP 800-115: NIST’s technical guide to information security testing and assessment.
- OWASP Web Security Testing Guide and ASVS: the reference for testing web applications and the requirements they should meet.
- OWASP API Security Top 10 and OWASP MASTG: guidance for API and mobile application testing.
- OSSTMM: a methodology focused on measuring operational security.
- MITRE ATT&CK: a knowledge base of real adversary techniques, used to map findings and plan realistic attack scenarios, especially in internal and red team testing.
When you evaluate a provider, ask which of these they follow and how they adapt them to your environment.
What a Good Penetration Test Report Includes
The report is what you are really paying for. A strong report is useful to two audiences: leadership, who need to understand risk, and engineers, who need to fix the issues. It should include:
- Executive summary: overall risk level, the most important findings and what they mean for the business, in non-technical language.
- Scope and methodology: what was tested, when, from where and under which constraints.
- Attack narrative: how individual weaknesses were chained into a path to sensitive data or systems.
- Detailed findings: for each issue, a description, affected assets, risk rating (for example using CVSS), step-by-step reproduction, evidence such as requests and screenshots, and business impact.
- Remediation guidance: specific, practical fixes, not generic advice such as “apply best practices”.
- Retest results: confirmation of which findings have been fixed.
Be cautious with reports that are mostly exported scanner output with a cover page. If a report has no evidence of manual exploitation and no attack narrative, it is a vulnerability scan, not a penetration test. For a detailed walkthrough, see what to expect in a penetration test report.
How Often Should You Run a Penetration Test?
The common baseline is at least once a year and after every significant change. PCI DSS, for example, requires internal and external penetration testing at least every 12 months and after significant infrastructure or application changes, and ISO/IEC 27001 expects technical vulnerabilities to be managed through regular testing.
In practice, frequency should follow how fast your environment changes:
- Before launching a new application, API or major feature
- After significant changes, such as a new authentication system, a cloud migration or a major infrastructure redesign
- After a security incident, to confirm the attacker’s path is closed
- Before a funding round, acquisition or major customer contract, when security due diligence is likely
- Continuously or quarterly for fast-moving SaaS products, often combined with automated testing in the CI/CD pipeline
An annual test of an application that ships every week leaves long gaps. For those environments, combine periodic manual testing with DevSecOps practices that catch issues as code is written.
How to Prepare for a Penetration Test
A well-prepared test produces better results in the same amount of time. Before testing starts:
- Define clear goals. Compliance evidence, a pre-launch check and an assessment of your most critical asset each call for a different scope.
- List everything in scope. Domains, IP ranges, applications, API documentation and cloud accounts. Missing assets mean missing findings.
- Prepare test accounts. Provide accounts for each user role, including two accounts per role so testers can check whether one user can reach another’s data.
- Choose the environment carefully. Testing in production is the most realistic; a staging environment that mirrors production is safer for destructive tests. Agree on this explicitly.
- Inform the right people. Your security operations team, hosting provider and key stakeholders should know a test is running, unless detection is part of what you are testing.
- Take backups of critical systems and data.
- Name an emergency contact on both sides who can be reached during testing hours.
- Plan remediation time. Reserve engineering capacity after the report so findings are actually fixed before the retest.
How to Choose a Penetration Testing Provider
The quality of a penetration test depends almost entirely on the people doing it. When comparing providers, look at:
- Manual testing depth. Ask how much of the engagement is manual and how they test authorization and business logic. Automated scanning alone is not a penetration test.
- Tester experience and certifications. Certifications such as OSCP, OSWE, CRTO or GPEN indicate hands-on skills; ask who will actually perform the test.
- Methodology. The provider should be able to explain which standards they follow and how they adapt them to your environment.
- Sample report. Request a redacted example. It shows more about quality than any sales presentation.
- Research and community work. Teams that publish vulnerability research and CVE analyses, such as our wp2shell and GitLab GraphQL analyses, tend to bring current attack knowledge to every engagement.
- Retest and support. Check whether retesting is included and whether testers are available to answer your developers’ questions.
- Data handling and confidentiality. Ask how findings, credentials and evidence are stored, encrypted and deleted after the engagement.
Red flags: a very low fixed price with no scoping call, a promise to test everything in one or two days, a report delivered without any evidence of exploitation, or a provider unwilling to share who will perform the work.
Common Penetration Testing Mistakes to Avoid
- Scoping too narrowly. Testing only the main website while APIs, mobile apps and admin panels stay out of scope leaves the real attack surface untested.
- Treating the test as a checkbox. A test run only to produce a compliance document rarely leads to real improvement.
- Not fixing the findings. The same issues appearing in next year’s report is a common and costly pattern. Track every finding to closure.
- Skipping the retest. Without verification, you do not know whether a fix actually works.
- Testing once and assuming you are secure. A penetration test is a snapshot. New code, new infrastructure and new vulnerabilities change the picture constantly.
- Ignoring low and medium findings. Attackers chain small issues together. Several medium findings can add up to a critical attack path.
Frequently asked questions
Conclusion
Penetration testing shows you your organization the way an attacker sees it. Done well, it goes beyond a list of vulnerabilities: it proves what is exploitable, explains the business impact and gives your teams a clear path to fix the issues that matter most.
The most effective approach is to treat penetration testing as part of a continuous security program: test before launches and after major changes, fix and retest every finding, and combine manual testing with automated checks throughout development.
Ready to see what an attacker would find? Explore our penetration testing services or talk to our team to scope your first engagement. If you want your own engineers to learn these techniques, see our penetration testing training programs.
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