Pen Testing (Penetration Testing): Complete Guide to Methods, Tools & Process

Pen testing (penetration testing) is an authorized simulated cyberattack conducted by ethical hackers to identify security vulnerabilities in systems, networks, and applications before malicious actors can exploit them. By thinking and acting like real attackers, penetration testers help organizations discover weaknesses in their defenses and strengthen security posture proactively.

This comprehensive guide explores everything you need to know about penetration testing, from the five phases and testing methodologies to essential tools, best practices, and how to implement an effective pen testing program.

What is Pen Testing (Penetration Testing)?

Penetration testing, commonly called pen testing or ethical hacking, is a security assessment where authorized professionals attempt to exploit vulnerabilities in computer systems, networks, web applications, or physical security controls to identify weaknesses that could be leveraged by malicious attackers.

Unlike automated vulnerability scans that simply identify potential issues, penetration testing involves skilled security professionals who:

• Think like attackers: Use real-world attack techniques and methodologies
• Chain exploits: Combine multiple vulnerabilities to achieve deeper access
• Validate impact: Determine actual exploitability and business risk
• Test controls: Evaluate effectiveness of existing security measures
• Provide actionable guidance: Deliver prioritized remediation recommendations

Why Penetration Testing is Critical

1. Identifies Real-World Exploitable Vulnerabilities

Automated scanners flag thousands of potential issues, but many are false positives or theoretical risks. Penetration testing validates which vulnerabilities are actually exploitable and how attackers could chain them together for maximum impact.

2. Provides Attacker's Perspective

Pen testers think like adversaries, using the same tactics, techniques, and procedures (TTPs) employed by real threat actors. This perspective reveals blind spots that traditional security assessments miss.

3. Tests Security Control Effectiveness

Organizations invest heavily in firewalls, IDS/IPS, EDR, and other security tools. Penetration testing validates whether these controls actually prevent attacks or can be bypassed.

4. Meets Compliance Requirements

Many regulatory frameworks mandate regular penetration testing:

• PCI DSS: Annual external and internal pen tests after significant changes
• HIPAA: Periodic technical and non-technical evaluations
• SOC 2: Regular security assessments to validate controls
• ISO 27001: Penetration testing as part of ISMS
• GDPR: Regular security testing and evaluation

5. Reduces Breach Risk and Costs

The average data breach costs $4.45 million (IBM, 2023). Proactive penetration testing, costing $5K-$50K, is far more cost-effective than recovering from a real attack.

6. Improves Security Awareness

Pen test findings educate development teams, IT staff, and executives about security risks and the importance of secure configuration, coding practices, and security investments.

Types of Penetration Testing

Penetration tests can target different aspects of an organization's attack surface:

1. Network Penetration Testing

Focus: Network infrastructure, firewalls, routers, switches, IDS/IPS, VPNs, and network segmentation.

What is tested:

• Network architecture and segmentation
• Firewall rule effectiveness
• Router and switch configurations
• Wireless network security
• Network-based attack vectors

Common techniques: Port scanning, vulnerability exploitation, man-in-the-middle attacks, network sniffing, VLAN hopping

2. Web Application Penetration Testing

Focus: Web applications, APIs, authentication mechanisms, and application logic vulnerabilities.

What is tested:

• OWASP Top 10 vulnerabilities (SQL injection, XSS, broken authentication)
• Business logic flaws
• Authentication and session management
• API security
• Input validation and output encoding

Common techniques: SQL injection, cross-site scripting (XSS), CSRF, authentication bypass, parameter tampering

3. Mobile Application Penetration Testing

Focus: iOS and Android applications, mobile APIs, local data storage, and communication security.

What is tested:

• Insecure data storage
• Weak cryptography
• Improper platform usage
• Insecure communication
• Code tampering and reverse engineering

4. Cloud Penetration Testing

Focus: Cloud infrastructure (AWS, Azure, GCP), containers, serverless functions, and cloud-native services.

What is tested:

• IAM misconfigurations
• Publicly exposed resources
• Container security
• Serverless function vulnerabilities
• Cloud storage permissions

5. Social Engineering Testing

Focus: Human vulnerabilities through phishing, pretexting, baiting, and physical intrusion.

What is tested:

• Employee susceptibility to phishing emails
• Phone-based social engineering (vishing)
• Physical security controls
• USB drop attacks
• Credential harvesting effectiveness

6. Physical Penetration Testing

Focus: Physical security controls, building access, and on-premises security.

What is tested:

• Badge/card access systems
• Security guard effectiveness
• Lock picking and tailgating
• Surveillance system blind spots
• Server room and data center security

7. Internal vs External Testing

External Pen Test: Simulates attacks from outside the network perimeter (internet-facing systems), mimics external threat actors.

Internal Pen Test: Simulates attacks from inside the network, mimics malicious insiders or compromised accounts after initial breach.

Testing Approaches: Black Box, White Box, Grey Box

Pen tests vary based on how much information the tester receives about the target systems:

Black Box Testing (Zero Knowledge)

Information provided: Minimal to none, only company name and public information.

Simulates: External attacker with no insider knowledge

Pros:

• Most realistic external attack scenario
• Tests security from true outsider perspective
• Reveals what attackers can discover publicly

Cons:

• Time-intensive reconnaissance phase
• May miss internal vulnerabilities
• Lower coverage due to limited knowledge

Best for: Testing external defenses, evaluating exposure to outside threats

White Box Testing (Full Knowledge)

Information provided: Complete system information, source code, architecture diagrams, credentials, network maps.

Simulates: Malicious insider or comprehensive security assessment

Pros:

• Most comprehensive coverage
• Efficient use of testing time
• Identifies maximum number of vulnerabilities
• Better for code review and logic flaws

Cons:

• Less realistic attack scenario
• Doesn't test reconnaissance defenses
• More expensive due to depth of analysis

Best for: Comprehensive security assessments, pre-production testing, code-level vulnerability analysis

Grey Box Testing (Partial Knowledge)

Information provided: Limited information, some credentials, partial documentation, user-level access.

Simulates: Privileged user, partner with limited access, or attacker who has gained initial foothold

Pros:

• Balances realism with efficiency
• Focus on critical systems faster
• Simulates common breach scenarios
• Most popular approach

Cons:

• Less realistic than black box
• Less comprehensive than white box

Best for: Most organizational assessments, balancing realism and coverage

The 5 Phases of Penetration Testing

Professional penetration testing follows a structured methodology:

Phase 1: Reconnaissance (Information Gathering)

Objective: Gather as much information as possible about the target organization, systems, and people.

Techniques:

• Passive reconnaissance: OSINT (Open Source Intelligence), Google dorking, social media mining, WHOIS lookups, DNS enumeration
• Active reconnaissance: Port scanning, service enumeration, network mapping, banner grabbing

Information collected:

• IP ranges and network architecture
• Domain names and subdomains
• Email addresses and employee names
• Technologies and software versions
• Public-facing services and applications

Tools: Maltego, theHarvester, Shodan, Censys, Recon-ng, Nmap, Whois

Phase 2: Scanning (Vulnerability Assessment)

Objective: Identify potential vulnerabilities, open ports, services, and entry points.

Techniques:

• Port scanning: Identify open ports and services
• Vulnerability scanning: Automated detection of known vulnerabilities
• Service enumeration: Detailed analysis of running services
• Network mapping: Understand network topology

Tools: Nmap, Nessus, OpenVAS, Qualys, Burp Suite, Nikto, SQLMap

Phase 3: Gaining Access (Exploitation)

Objective: Exploit identified vulnerabilities to gain unauthorized access to systems or applications.

Techniques:

• Exploiting known vulnerabilities (CVEs)
• SQL injection and XSS attacks
• Password attacks (brute force, credential stuffing)
• Social engineering
• Privilege escalation

Goals:

• Initial foothold on target systems
• Escalate privileges to administrator/root
• Access sensitive data
• Lateral movement to other systems

Tools: Metasploit Framework, SQLMap, Hydra, Cobalt Strike, Empire, BeEF

Phase 4: Maintaining Access (Persistence)

Objective: Determine if persistent access can be maintained, simulating advanced persistent threats (APTs).

Techniques:

• Installing backdoors
• Creating rogue accounts
• Modifying system files
• Deploying web shells
• Establishing command and control (C2) channels

Purpose: Demonstrate how attackers could maintain long-term access for data exfiltration, espionage, or future attacks.

Tools: Meterpreter, web shells, PowerShell Empire, custom malware

Phase 5: Analysis and Reporting

Objective: Document findings, assess business impact, and provide actionable remediation recommendations.

Report components:

• Executive summary: High-level findings for non-technical stakeholders
• Technical details: Vulnerability descriptions, exploitation steps, evidence
• Risk ratings: CVSS scores and business impact assessment
• Remediation guidance: Specific, actionable fix recommendations
• Timeline and scope: Testing dates, systems tested, methodologies used

Deliverables:

• Comprehensive written report
• Executive presentation/debrief
• Prioritized remediation roadmap
• Retest after fixes (often included)

Pen Testing Methodologies and Standards

Professional penetration testing follows established frameworks to ensure thoroughness and consistency:

OWASP Testing Guide

Focus: Web application security testing

Coverage: Comprehensive methodology for testing web app vulnerabilities including the OWASP Top 10

PTES (Penetration Testing Execution Standard)

Focus: General penetration testing framework

Coverage: Seven phases from pre-engagement to reporting, widely adopted by industry

NIST SP 800-115

Focus: Technical guide to information security testing

Coverage: Government standard for security assessment and penetration testing

OSSTMM (Open Source Security Testing Methodology Manual)

Focus: Comprehensive security testing across all channels

Coverage: Human, physical, wireless, telecommunications, and data networks

MITRE ATT&CK Framework

Focus: Adversary tactics, techniques, and procedures

Coverage: Real-world attack patterns used to guide testing and validate detection capabilities

Essential Penetration Testing Tools

1. Kali Linux

Type: Operating system and toolkit

Description: Debian-based Linux distribution pre-loaded with 600+ security tools, the de facto standard for pen testing.

2. Metasploit Framework

Type: Exploitation framework

Description: Most popular penetration testing framework with thousands of exploits, payloads, and auxiliary modules.

3. Burp Suite

Type: Web application security testing

Description: Industry-standard proxy tool for web app testing, intercepts and modifies HTTP traffic, automated scanning.

4. Nmap

Type: Network scanning

Description: Network discovery and security auditing, port scanning, service detection, OS fingerprinting.

5. Wireshark

Type: Network protocol analyzer

Description: Packet capture and analysis tool, deep inspection of network traffic.

6. John the Ripper / Hashcat

Type: Password cracking

Description: Password hash cracking tools, dictionary attacks, brute force, rainbow tables.

7. SQLMap

Type: SQL injection automation

Description: Automated SQL injection detection and exploitation tool.

8. Cobalt Strike

Type: Adversary simulation and red team operations

Description: Commercial platform for post-exploitation and covert operations (often used in advanced engagements).

9. Nessus / OpenVAS

Type: Vulnerability scanners

Description: Automated vulnerability scanning and assessment tools.

10. Social Engineering Toolkit (SET)

Type: Social engineering attacks

Description: Framework for conducting social engineering assessments including phishing and credential harvesting.

Pen Testing vs Vulnerability Scanning vs Red Teaming

Bottom line: Vulnerability scanning identifies "what could be wrong," penetration testing proves "what is actually exploitable," and red teaming tests "how well you can detect and respond to real attacks."

How to Conduct a Penetration Test

Organizations implementing penetration testing should follow this process:

Step 1: Define Objectives and Scope

• What systems/applications will be tested?
• What is in-scope vs out-of-scope?
• What testing approach (black/white/grey box)?
• What business goals drive the test?
• Are there any constraints or restrictions?

Step 2: Establish Rules of Engagement

• Testing timeframe and schedule
• Authorized testing methods
• Escalation procedures and emergency contacts
• Data handling and confidentiality requirements
• Notification requirements

Step 3: Obtain Written Authorization

Critical legal protection, document explicitly states authorization to conduct security testing. Include:

• Specific systems and IP ranges authorized
• Testing dates and duration
• Authorized personnel
• Legal protections and liability limitations

Step 4: Execute Testing

Follow the five phases (reconnaissance, scanning, exploitation, persistence, analysis) using appropriate methodologies and tools.

Step 5: Document Everything

Maintain detailed records of:

• Every action taken
• Vulnerabilities discovered
• Exploitation steps and evidence
• Systems accessed
• Data encountered

Step 6: Deliver Report and Debrief

Present findings to stakeholders with clear, actionable recommendations prioritized by risk.

Step 7: Retest After Remediation

Validate that fixes effectively address vulnerabilities, many engagements include one retest cycle.

Reporting and Remediation

An effective penetration testing report should include:

Executive Summary

• High-level findings in business terms
• Overall risk assessment
• Key recommendations
• Statistics (vulnerabilities by severity, exploitation success rate)

Technical Findings

For each vulnerability:

• Vulnerability name and description
• Risk rating: Critical/High/Medium/Low with CVSS score
• Affected systems: Specific hosts, applications, or services
• Evidence: Screenshots, logs, command outputs
• Impact analysis: What attacker could achieve
• Remediation guidance: Specific steps to fix
• References: CVE IDs, security advisories, best practices

Remediation Roadmap

Prioritized plan for addressing findings:

• Immediate (0-30 days): Critical vulnerabilities with high exploitability
• Short-term (30-90 days): High-risk issues
• Medium-term (90-180 days): Medium-risk issues
• Long-term (180+ days): Low-risk issues and security enhancements

How Often Should You Pen Test?

Industry best practices:

Annual Penetration Testing (Minimum)

Conduct comprehensive penetration tests at least once per year, this is the baseline for most compliance frameworks.

After Significant Changes

Perform targeted pen tests after:

• Major infrastructure changes
• New application deployments
• Network architecture modifications
• Major system upgrades or patches

Compliance-Driven Testing

• PCI DSS: Annual and after significant changes; quarterly for some environments
• HIPAA: Periodic testing as part of risk management
• SOC 2: Regular testing aligned with audit cycle

Continuous Security Validation

Mature organizations implement:

• Quarterly pen testing: Different areas each quarter
• Continuous vulnerability assessment: Automated scanning
• Purple team exercises: Collaborative security testing
• Bug bounty programs: Crowdsourced ongoing testing

Choosing a Penetration Testing Provider

When selecting a penetration testing firm or consultant, evaluate:

1. Credentials and Certifications

Look for:

• Individual certifications: OSCP, GPEN, CEH, GWAPT, OSCE
• Company certifications: CREST, CHECK, Tiger Scheme
• Compliance: SOC 2 Type II, ISO 27001

2. Experience and Expertise

• Years in business and number of engagements performed
• Industry-specific experience
• Technology stack expertise (cloud, mobile, IoT, etc.)
• References and case studies

3. Methodology and Approach

• Adherence to recognized standards (PTES, OWASP, NIST)
• Testing depth and thoroughness
• Manual testing vs automated scanning reliance
• Customization capabilities

4. Reporting Quality

• Request sample reports
• Evaluate clarity and actionability
• Executive and technical audience appropriateness
• Remediation guidance quality

5. Communication and Support

• Responsiveness during engagement
• Escalation procedures for critical findings
• Post-test support and retest offerings
• Executive debrief and Q&A sessions

6. Insurance and Legal Protections

• Errors and omissions (E&O) insurance
• Cyber liability coverage
• Clear contracts and legal safeguards

Penetration Testing Best Practices

For Organizations Commissioning Pen Tests:

1. Define clear objectives aligned with business risk
2. Establish realistic scope, don't test everything at once if budget limited
3. Obtain stakeholder buy-in, ensure IT, security, and leadership support
4. Notify key personnel (but consider limited notification for realistic testing)
5. Plan for disruption, testing can cause temporary service impacts
6. Prioritize remediation, act on findings quickly, especially critical issues
7. Retest after fixes, validate that remediation is effective
8. Integrate into SDLC, test applications before production deployment
9. Combine with other assessments, vulnerability scans, code reviews, architecture reviews
10. Track metrics over time, measure security posture improvement

For Penetration Testers:

1. Always obtain written authorization, never test without explicit permission
2. Understand business context, know what systems are critical
3. Follow established methodologies, be thorough and repeatable
4. Document everything, maintain detailed evidence
5. Communicate findings promptly, escalate critical issues immediately
6. Write clear, actionable reports, provide value beyond finding problems
7. Respect confidentiality, protect client data and findings
8. Stay current, continuously learn new techniques and vulnerabilities
9. Think like an attacker, but act ethically and professionally

Frequently Asked Questions

What is pen testing?

Pen testing (penetration testing) is an authorized simulated cyberattack on a computer system, network, or web application to identify exploitable vulnerabilities. Ethical hackers use the same tools and techniques as malicious attackers to find security weaknesses before real criminals can exploit them.

What are the 5 phases of penetration testing?

The 5 phases are:

1. Reconnaissance: Information gathering about targets
2. Scanning: Identifying vulnerabilities and entry points
3. Gaining Access: Exploiting vulnerabilities
4. Maintaining Access: Determining persistence potential
5. Analysis and Reporting: Documenting findings and recommendations

What is the difference between black box, white box, and grey box testing?

• Black box testing: No internal knowledge provided, simulates external attacker
• White box testing: Complete system knowledge provided, simulates insider or comprehensive assessment
• Grey box testing: Partial knowledge provided, simulates privileged user with limited access

How much does penetration testing cost?

Penetration testing costs vary widely based on scope and complexity:

• Basic web app test: $3,000-$10,000
• Network penetration test: $10,000-$50,000
• Comprehensive assessment: $25,000-$100,000+

Factors affecting cost include number of systems, testing depth, duration, whether it includes social engineering, and if remediation retesting is included.

What's the difference between penetration testing and vulnerability scanning?

Vulnerability scanning is automated scanning that identifies potential security issues, fast and broad but produces many false positives. Penetration testing is manual exploitation by security experts who validate vulnerabilities, chain exploits, and prove actual impact, more thorough but time-intensive and expensive. Think of scanning as "what might be wrong" and pen testing as "what attackers can actually exploit."

How long does a penetration test take?

Duration varies by scope:

• Web application: 3-10 days
• Network (external): 5-15 days
• Network (internal): 7-21 days
• Comprehensive (network + apps): 2-6 weeks

This includes reconnaissance, exploitation, and reporting phases.

How often should you conduct penetration testing?

Industry best practice recommends:

• Annual minimum: Comprehensive pen test once per year
• After significant changes: New systems, major updates, infrastructure changes
• Before major launches: New product releases or services
• Compliance-driven: PCI DSS requires annual external testing and after significant changes

Mature organizations conduct quarterly testing of different areas.

Is penetration testing legal?

Penetration testing is legal ONLY when conducted with explicit written authorization from the system owner. Unauthorized access to computer systems violates laws like the Computer Fraud and Abuse Act (US), Computer Misuse Act (UK), and similar laws globally. Always obtain proper authorization, define scope clearly, and work within rules of engagement.

What certifications do penetration testers have?

Common penetration testing certifications include:

• OSCP: Offensive Security Certified Professional, hands-on, highly respected
• CEH: Certified Ethical Hacker, entry to mid-level
• GPEN: GIAC Penetration Tester, comprehensive technical knowledge
• GWAPT: GIAC Web Application Penetration Tester, web app focus
• OSCE: Offensive Security Certified Expert, advanced exploitation
• CREST: UK-based certification framework for pen testers

Can I do my own penetration testing?

Yes, but consider:

• Legal authorization: You must own the systems or have explicit permission
• Skills required: Effective pen testing requires deep technical expertise
• Tools and infrastructure: Proper testing environment and toolsets
• Objectivity: External testers provide unbiased perspective
• Compliance: Many frameworks require independent third-party testing

For critical systems or compliance requirements, professional penetration testing is recommended.

What should I do with penetration testing results?

1. Triage findings: Prioritize by risk and business impact
2. Address critical issues immediately: Patch or mitigate high-risk vulnerabilities within 30 days
3. Create remediation plan: Timeline for addressing all findings
4. Assign ownership: Designate responsible parties for each fix
5. Track progress: Monitor remediation completion
6. Retest: Validate that fixes are effective
7. Update processes: Implement controls to prevent recurrence
8. Report to stakeholders: Keep leadership informed of security posture