Most teams come to this with the same worries: internet-facing assets nobody inventoried, flat networks, an audit on the calendar, a thin security team, and a scanner report full of findings with no clue which ones matter. Exposure is real. The Verizon 2026 DBIR found vulnerability exploitation was the initial access route in 31% of breaches, with credential abuse at 13%.
This guide covers testing types and scope, the seven stages, common findings, planning, reporting, remediation, and retesting.
Key Takeaways
- Pentesting validates weaknesses through controlled exploitation; scanning only flags possible ones.
- External and internal tests answer different questions, so pick by threat model.
- Black, gray, and white box describe tester knowledge, not test position.
- The report and fix-and-retest cycle matter as much as the test.
What Is Network Penetration Testing?
Network penetration testing is a controlled, authorized assessment of network infrastructure, devices, services, and access controls. Testers use realistic attacker techniques. The NIST glossary notes that such tests can combine vulnerabilities to gain greater access.
Depending on objectives, a scope may include:
- Internet-facing assets, firewalls, VPNs, and routers
- Cloud connections and remote access paths
- Internal segments and wireless networks
- Identity-related controls such as Active Directory
Every test needs written permission, approved rules of engagement, defined exclusions, emergency contacts, and safeguards against unnecessary disruption.
Penetration Testing vs. Vulnerability Scanning
Scanning identifies known weaknesses at scale. Penetration testing confirms which ones are exploitable, chains them together, and shows business impact.
A scanner reports a missing patch. A pentest shows how that patch gap becomes a foothold, how the foothold yields a service-account credential, and how that credential reaches a file server and then backup infrastructure. That chain is what DeepSeas RED traces in its network tests.
Why a Pentest Is Not a Complete Security Program
A pentest is a point-in-time snapshot. It cannot replace:
- Patch management and secure configuration
- Identity controls
- Continuous monitoring
- Incident response and governance
A clean report reflects conditions on the test date, not next quarter. Pair periodic tests with ongoing monitoring.
Network Penetration Testing Types and Scope
External vs. Internal Network Penetration Testing
External testing simulates an attacker outside the perimeter. It covers public IP addresses, exposed services, firewalls, VPN gateways, remote access, and cloud-hosted assets, including ones the security team doesn't know exist.
Internal testing assumes an attacker, insider, compromised account, or infected endpoint already has access. It evaluates discovery, privilege escalation, lateral movement, trust relationships, and segmentation.
Black-Box, Gray-Box, and White-Box Testing
These terms describe starting knowledge. The PCI Security Standards Council defines them this way:
| Model | Tester knowledge | Useful for |
|---|---|---|
| Black box | No prior knowledge of internal design | Modeling an outside attacker and observable attack surface |
| Gray box | Partial knowledge, such as credentials | Authenticated access and insider risk |
| White box | Full diagrams and configurations | Defensive depth and efficient coverage |
Any of these can be run externally or internally. They are separate choices.
Choosing the Right Scope and Perspective
Let business drivers set scope:
- Recent infrastructure changes or cloud migration
- Known incidents
- Compliance requirements
- Mergers or acquisitions
- Remote access expansion
- Sensitivity of the systems involved
Combined engagements are common. An external test followed by an internal test shows how far an outside breach could travel. Teams also pair network tests with cloud, wireless, application, OT, or social engineering assessments where those risks apply.
The 7 Stages of Network Penetration Testing
The Seven-Stage Workflow
The seven stages follow the Penetration Testing Execution Standard (PTES). NIST SP 800-115 uses four phases (planning, discovery, attack, reporting), so treat seven as a common framework, not a universal one.
- Planning and authorization. Define objectives, assets, threat scenarios, stakeholders, legal approval, exclusions, success criteria, and communication procedures before any testing.
- Reconnaissance and attack-surface discovery. Identify approved domains, IP ranges, technologies, exposed services, and remote access points without exceeding scope.
- Scanning and enumeration. Find live hosts, open ports, service versions, and authentication surfaces, controlling scan intensity.
- Vulnerability validation and controlled exploitation. Confirm whether high-value findings are exploitable. Capture evidence, avoid destructive actions, and avoid unnecessary access to sensitive data.
- Post-exploitation and lateral-movement assessment. Determine what an attacker could reach, whether privileges expand, and whether segmentation, identity controls, or monitoring limit the damage.
- Impact analysis and reporting. Translate technical findings into business risk in a prioritized report.
- Remediation support and retesting. Help fix issues, then verify that material weaknesses were closed.
What Testers Should Document
Good records make the report reproducible and useful to engineers and executives alike. Capture:
- Timestamps and affected assets
- Attack paths and supporting evidence
- Access obtained and assumptions made
- Safety decisions and limitations
Documenting each step also shows exactly where an attack chain could have been broken.
Common Network Vulnerabilities and What Testing Reveals
The CISA and NSA misconfiguration advisory lists ten common problems seen in real assessments. It is an observation list, not a prevalence ranking. Here is how they show up in testing.
Exposed Ports, Services, and Internet-Facing Assets
- Unnecessary exposed services and outdated protocols
- Insecure remote administration
- Forgotten public assets
- Weak VPN setups
- Cloud or firewall rules that broaden access by accident
Edge devices are frequent targets. CISA's list of routinely exploited vulnerabilities includes Citrix NetScaler (CVE-2023-3519, CVE-2023-4966) and Fortinet SSL-VPN (CVE-2023-27997).
Weak Authentication, Credentials, and Privileges
Testers look for:
- Weak password policies
- Reused or default credentials
- Excessive privileges and exposed admin interfaces
- Incomplete or inconsistent MFA
- Service accounts and access that survives role changes or departures
CISA's advisory describes a printer accessible with default credentials, then privileged domain accounts used for lateral movement and domain compromise.
Misconfigured Firewalls, Routers, Switches, and Services
- Insecure management interfaces
- Overly permissive rules
- Unsafe defaults and weak encryption settings
- Misconfigured DNS or DHCP
- Unneeded device features
- Missing administrative access restrictions
Poor Segmentation and Lateral-Movement Paths
Internal testing reveals whether a compromised workstation, guest network, or vendor connection can reach payment environments, healthcare systems, critical servers, or operational technology. Flat networks turn one foothold into many.
Outdated Systems, Legacy Protocols, and Weak Detection
Expect unpatched operating systems, unsupported appliances, insecure legacy protocols, thin logging, and missing alerting. A test often exposes the gap between stated controls and what actually happens.
Modern and Specialized Environments
Scope may need to cover hybrid cloud, distributed offices, wireless, BYOD, remote workers, third-party connections, and managed services. OT/ICS and production systems demand extra safety planning and specialized expertise. NIST SP 800-82 Rev. 3 calls for offline testing of scanning tools before production use.
How to Plan, Report, and Act on a Network Penetration Test
Before Testing: Scope, Rules of Engagement, and Readiness
Run through this checklist:
- Written authorization signed by the team leader and senior management
- In-scope and out-of-scope assets
- Test windows and production restrictions
- Emergency stop procedures and stakeholder contacts
- Data-handling expectations
- Coordination with your SOC or managed security provider
Reading the Report and Prioritizing Findings
A useful report includes:
- Executive summary and methodology
- Scope and limitations
- Attack narrative with evidence
- Affected assets and severity rationale
- Business impact and remediation recommendations
- A clear line between confirmed findings and observations
From Remediation to Continuous Improvement
- Assign an owner to every finding.
- Prioritize by risk and document compensating controls.
- Retest fixes. PCI DSS v4.0.1 requires repeat testing to verify corrections.
- Update configurations and policies.
- Use continuous monitoring to catch new exposure between tests.
Cadence depends on your obligations. PCI DSS requires internal and external tests at least every 12 months and after significant changes. CMMC Level 3 says annually or when significant security changes are made. HIPAA's current rule requires risk analysis and periodic evaluation, but it does not mandate an annual pentest.
When to Use an External Security Partner
An independent provider helps when you lack offensive skills, need an objective assessment, face an audit or customer security review, or want findings tied to broader GRC work.
DeepSeas is one example. It has nearly 30 years of cyber defense experience, ISO Lead Auditor-certified specialists, and offensive security services for enterprise, mid-market, regulated, government, and education organizations.
Its network testing covers networks, Active Directory, APIs, wireless, and cloud, and includes free remediation testing within six months.
Frequently Asked Questions
What is penetration testing in networking?
It is an authorized simulation of attacks against network infrastructure. The goal is to find exploitable weaknesses and demonstrate their potential impact.
What are the main three types of penetration testing?
Black-box, gray-box, and white-box, which describe how much the tester knows up front. Internal and external are separate scope classifications.
What are the 7 stages of penetration testing?
Planning and authorization, reconnaissance, scanning and enumeration, validation and exploitation, post-exploitation and lateral movement, impact analysis and reporting, then remediation and retesting.
How is network penetration testing different from vulnerability scanning?
Scanning automatically flags potential weaknesses. Pentesting validates which are exploitable and what they enable.
How often should an organization perform network penetration testing?
Follow risk, compliance duties, major changes, incidents, and exposure shifts. PCI DSS sets at least every 12 months, and periodic tests should complement continuous monitoring.
