The Complete Guide to External Penetration Testing (2026)
External penetration tests are one of the most common tests we perform. An external penetration test is often the starting point for any company that is trying to understand its risk. With numerous compliance regulations (PCI, GDPR, HIPAA, CMMC, etc) either requiring external penetration tests or “highly recommending” them, we get to perform a lot of them. As such, we decided to put together this blog to inform people on what an external penetration test is, what steps are involved to perform one, give you an idea of the costs associated with this type of test, how to avoid problems that may occur, and finally, how to improve your results. So let’s dive in.
What Is an External Penetration Test?
Simply put, an external penetration test emulates an attacker on the Internet trying to break into your organization. As such, an external penetration test is primarily concerned with your perimeter (Internet-facing) security and is focused on evaluating the strength of the security controls applied to your organization’s Internet-facing systems. The goal of an external penetration test isn’t just to run automated scans. Skilled penetration testers apply the same tactics used by real-world hackers, manually identifying and exploiting vulnerabilities to assess true risk. This approach reduces false positives, highlights critical weaknesses, and provides actionable insights that go beyond basic vulnerability scanning.
An external penetration test answers questions such as:
- What systems and services are accessible from the Internet?
- Is any software on my perimeter out of date or vulnerable?
- Can sensitive information be gathered about my organization through open source intelligence (OSINT)?
- Can a user’s password for email or VPN be easily guessed?
- Is my organization an easy target for an opportunistic attacker?
What Does External Penetration Testing Include?
A thorough external penetration test involves far more than running an automated scanner. Here are the core components of what a qualified external penetration test includes:
Open Source Intelligence (OSINT) / Reconnaissance
We’ll use publicly available resources to try and uncover sensitive information, such as types of technology used by the organization or potential usernames, files that were posted unintentionally, and other items that can be used in the later phases of testing.
Full Port Scan
In order to footprint an organization’s external perimeter, a port scan is used to understand which services are exposed and accepting inbound connections. These scans (usually leveraging tools like masscan and nmap) will take a look at all 65,535 TCP ports and the top 1000 most popular UDP ports.
Vulnerability Scanning
Where some assessments would center around a vulnerability scan, this is really just the beginning of an external penetration test. We use a vulnerability scan to speed up the identification process for some “low-hanging fruit” types of issues and exploitable weaknesses that could lead to a more significant compromise.
Unauthenticated Web Application Testing
Any web applications discovered on your perimeter are assessed from a blackbox (unauthenticated) perspective. Testers evaluate login pages, forms, and publicly accessible content for vulnerabilities such as injection attacks, authentication bypass, information disclosure, and misconfigurations. Note that this is different from a full web application penetration test, see the section below for the distinction.
Manual and Automated Exploit Attempts
This is really the bread and butter of an external penetration test, and the most important part of the assessment. It’s hard to completely cover everything that can happen during this portion of the attack, but it includes looking for vulnerabilities that automated scans can’t find, exploiting issues scans did find, understanding the risks associated with identified vulnerabilities, and noting any mitigating controls.
Password Attacks
Another important portion of external penetration testing is the opportunity for password attacks. These styles of attacks aim to use open source intelligence gathered and noted vulnerabilities, combining them in a way that makes password attacks more likely to succeed while avoiding protections in place. These attacks can help you understand shortcomings in password policies, account lockouts, and multi-factor authentication schemes.
Our External Penetration Testing Methodology
We base our external penetration testing methodology on established industry standards, several of which we’ve listed below. Our team also regularly attends top security conferences and is given dedicated time to stay current with the latest tools and trends. This approach ensures we align with best practices while staying grounded in proven, well-defined frameworks.
Open Web Application Security Project (OWASP) Testing Guide
Technical Guide to Information Security Testing and Assessment (NIST 800-115)
The Penetration Testing Execution Standard (PTES)
Payment Card Industry (PCI) Penetration Testing Guidance
Commonly Used Tools
| Category | Tools |
|---|---|
| Reconnaissance | Recon-ng, theHarvester, Google Dorking, Wayback Machine, Amass, Dehashed |
| Scanning | Nmap, Masscan, Nessus, Shodan |
| Web Application | Burp Suite Pro, Nikto, Dirbuster/GoBuster/Ferox, Sqlmap |
| Exploitation | Metasploit Framework, ExploitDB, Cobalt Strike, custom scripts |
| Password Attacks | Hashcat, MSOLSpray, FireProx, MFASweep, custom scripts |
Phase 1: Planning
Scoping: After initiating the project, scoping/target information will be collected from the client. In the case of external penetration testing, this information will include any applicable IP addresses and URLs in scope, defining any specific compromise goals with the client to help us focus our attacks, and working with the client to gather any information that can help us prevent issues during the test. For instance, knowing the account lockout policy and any web forms to avoid.
Rules of Engagement: Before testing begins, we hold a project kick-off meeting to review the scope, timeline, testing objectives, any exclusions, and to address questions. This is your opportunity to flag any systems that need special handling.
Phase 2: Execution
Reconnaissance: Once the test has officially begun, a start notification will be sent to the client. The first phase will involve open-source intelligence gathering, which includes a review of publicly available information and resources. The goal of this phase is to identify any sensitive information that may be helpful during the following phases of testing, which could include email addresses, usernames, software information, user manuals, forum posts, etc. Additionally, this step will include searching for sensitive information that should not be publicly available, such as internal communications, salary information, or other potentially harmful information.
Threat Modeling: For this assessment, the threat modeling phase serves to evaluate the types of threats that may affect the targets that are in scope. The types of attacks and likelihood of these threats materializing will serve to inform risk rankings/priorities that are assigned to vulnerabilities throughout the assessment. This phase of the assessment should also include host and service discovery, combining the passive methods of detection from step 1 with active enumeration. The ultimate goal of an external penetration test is to emulate an attacker on the Internet trying to break into your network. As such, during this stage, we will evaluate the targets in scope and determine an attack path that emulates real-world attacks.
Vulnerability Analysis: The vulnerability analysis phase will encompass the discovery and enumeration of all in-scope targets/applications. For each service discovered, automated and manual techniques will be used to attempt to find vulnerabilities with the in-scope targets. The engineer will attempt to identify the version of the service and investigate for previously published vulnerabilities. The engineer will also test the unauthenticated portion of web applications for vulnerabilities listed in the OWASP Top 10. Finally, each service will be manually inspected and tested for default credentials or other vulnerabilities that might be missed in an automated scan.
Exploitation: This phase will involve taking all potential vulnerabilities identified in the previous phases of the assessment and attempting to exploit them as an attacker would. This helps to evaluate the realistic risk level associated with the successful exploitation of the vulnerability, analyze the possibility of exploit/attack chains, and account for any mitigating controls that may be in place. Additionally, we’ll identify any false positives during this activity. Triaxiom will exploit automatically identified vulnerabilities and evaluate issues requiring manual identification and exploitation. Finally, for each login prompt discovered, default passwords and other password attacks will be attempted to try to gain access to in-scope systems.
Post-Exploitation: After successful exploitation, analysis will continue, including infrastructure analysis, pivoting, sensitive data identification, data exfiltration, and identification of high-value targets/data. We’ll use the information collected here in the prioritization and criticality ranking of identified vulnerabilities.
Phase 3: Post-Execution
Reporting: After completing the active portion of the assessment, Triaxiom will formally document the findings. The output provided will generally include an executive-level report and a technical findings report. The executive-level report is written for management consumption and includes a high-level overview of assessment activities, scope, most critical/thematic issues discovered, overall risk scoring, organizational security strengths, and applicable screenshots. The technical findings report, on the other hand, will include all vulnerabilities listed individually, with details as to how to recreate the issue, understand the risk, recommended remediation actions, and helpful reference links.
Quality Assurance: All assessments go through a rigorous technical and editorial quality assurance phase. This may also include follow-ups with the client to confirm or deny environment details, as appropriate.
Presentation: We walk you through the full report, answer questions, make any necessary updates, and schedule retesting if applicable.
What Is NOT Included in an External Penetration Test?
An external penetration test evaluates the risk from an outside attacker, but does not cover every possible attack vector. Two important areas are typically not included:
Authenticated Web Application Testing
An external penetration test includes unauthenticated web application testing, evaluating what an attacker can see and do without logging in. It does not include authenticated testing, where a tester is provided valid credentials and evaluates the application from the inside. A full web application penetration test evaluates role-based access controls, business logic flaws, e-commerce checkout security, and other application-layer risks that require authentication to discover.
| Testing Area | External Pen Test | Web App Pen Test |
|---|---|---|
| Unauthenticated testing | Included | Included |
| Login page attacks | Included | Included |
| Authenticated access testing | Not included | Included |
| Role-based access control | Not included | Included |
| Business logic / checkout | Not included | Included |
| Full OWASP Top 10 coverage | Partial | Full |
Social Engineering
No matter how well-secured your perimeter is, an employee clicking a malicious link can give an attacker a direct path into your internal network, bypassing all perimeter controls. Social engineering (phishing, spear-phishing, and vishing) is a separate engagement type and is not part of a standard external penetration test.
Common Findings on External Penetration Tests
After performing hundreds of external penetration tests, certain findings appear consistently across organizations of all sizes and industries. Here are the most common vulnerabilities we uncover:
Missing or Weak Multi-Factor Authentication (MFA)
The absence of MFA on Internet-facing login portals (particularly VPN, webmail, and external portals) is one of the most critical and most common findings we identify. When MFA is not enforced, password attacks become significantly more dangerous. An attacker who obtains or guesses a single set of credentials has a direct path into your network. Learn more about why MFA is so important.
Password Spraying Vulnerabilities
Password spraying is one of the most effective attacks we perform during external penetration tests. Unlike traditional brute-force attacks that target one account with many passwords, password spraying tries a single commonly used password across many accounts, avoiding lockout thresholds entirely. Read our detailed writeup on what a password spraying attack is and see a real-world password spraying vulnerability walkthrough from one of our engagements.
Outdated or Unpatched Software
Internet-facing software that has not been patched is a prime target. This includes web servers, firewalls, remote access tools, and content management systems. Patching Internet-facing systems promptly is one of the highest-impact things you can do to reduce your external risk.
Excessive Attack Surface
Many organizations expose far more services to the Internet than they realize. Open ports, forgotten test servers, development environments, and legacy applications that were never decommissioned all increase your attack surface and give attackers more opportunities. Every unnecessary service exposed to the Internet is a liability.
Sensitive Information Exposed via OSINT
During reconnaissance, we routinely discover sensitive organizational information that has been inadvertently made public, including employee email formats, software stack details, configuration files, and occasionally credentials in public code repositories. This information dramatically lowers the bar for an attacker before they have touched a single system.
SSL/TLS Misconfigurations
Weak encryption configurations, including support for deprecated protocols (SSL 3.0, TLS 1.0/1.1), weak cipher suites, and invalid or expired certificates, are common findings. These issues can expose data in transit to interception and reflect poorly on compliance posture for frameworks like PCI DSS.
Default Credentials
Network devices, administrative interfaces, and web applications that still use vendor-default usernames and passwords are an immediate critical finding. Default credentials are publicly documented and are one of the first things an attacker tries. We test every discovered login interface for default credentials as part of our standard methodology.
How to Reduce Your Attack Surface Before Testing
One of the most consistent themes we see across external penetration tests is an unnecessarily large attack surface. Here are the most impactful steps you can take:
- Remove unnecessary hosts: Every Internet-facing system should have a documented business justification. If it does not need to be Internet-facing, move it behind the firewall.
- Remove unnecessary services: A web server should serve web traffic only. Disable and block everything else at the firewall.
- Block traffic to unnecessary ports: Closed but reachable ports indicate firewall rules need updating. Traffic should never reach a port unless a service is intentionally listening there.
- Remove default content: Default help pages, configuration interfaces, and templates should never exist in production Internet-facing environments.
- Enforce MFA on all login interfaces: Multi-factor authentication is one of the single highest-impact controls you can implement.
- Ensure strong transport encryption: All exposed login interfaces should use HTTPS with TLS 1.2+ and strong cipher suites.
- Implement account lockout policies: All login interfaces should enforce lockout after a defined number of failed attempts.
Should You Test During Business Hours or After Hours?
A common scoping question is whether testing should be conducted after hours to minimize disruption. For most organizations, the answer is no, after-hours testing increases cost without meaningfully reducing risk. Your Internet-facing systems are already under continuous attack from automated scanners and real threat actors. If they cannot withstand a controlled, professional penetration test, that is critical information you need. Experienced testers avoid disruptive actions, throttle scanning traffic, and ask about fragile systems during kick-off so they can be handled appropriately.
After-hours testing is appropriate for highly regulated environments, systems with zero tolerance for disruption, or specific compliance requirements. But for the vast majority of organizations, business-hours testing is perfectly appropriate, less costly, and ensures your team is on hand to respond if anything unexpected occurs.
What Can Go Wrong During External Penetration Testing?
For 99% of our engagements, an external penetration test goes exactly as planned. Here are the uncommon issues that can arise and how to mitigate them:
System or Network Outage
Active exploitation of vulnerabilities carries residual risk. Fragile or unpatched systems may react unpredictably.
Mitigation: Flag any legacy or business-critical Internet-facing systems during the kick-off call so the team can handle them with appropriate caution or schedule testing for off-hours.
Data Corruption
Certain vulnerability classes (particularly SQL Injection) carry a risk of inadvertent data modification.
Mitigation: Verify that your organizational backups and restoration procedures are current before testing begins.
Discovering You Have Already Been Compromised
It is uncommon, but we have discovered during testing that a client’s systems were already compromised by a real attacker. If this occurs, we immediately stop testing, notify your point of contact, and assist with response and remediation.
Mitigation: Implement continuous monitoring of Internet-facing systems to detect potential breaches as early as possible.
How Much Does an External Penetration Test Cost?
The cost of an external penetration test is primarily driven by the time a qualified engineer spends evaluating your environment. Scope (specifically, the number of IP addresses on your Internet perimeter with at least one open port accepting connections) is the biggest single cost driver.
| Organization Size | External Hosts (Live IPs) | Approximate Cost Range |
|---|---|---|
| Small | Fewer than 10 | ~$5,000 |
| Medium | 10–50 | $8,000–$15,000 |
| Large | 50+ | $15,000–$20,000+ |
Additional factors that affect pricing include the testing approach (black box vs. gray box vs. white box), whether after-hours testing is required, and the number of reports required at the end. Be cautious of unusually low quotes for even a small environment are almost certainly automated vulnerability scans, not true penetration tests.
Frequently Asked Questions About External Penetration Testing
Most external penetration tests are completed within 3–5 business days of active testing. The full engagement, which includes scoping, kick-off, testing, reporting, and final presentation, typically spans 2–3 weeks from start to finish.
At a minimum, annually. Most compliance frameworks including PCI DSS, FedRAMP, and CMMC require at least annual testing, and many also require retesting after significant infrastructure changes.
A vulnerability scan is an automated tool that identifies known vulnerabilities based on software versions and signatures but does not exploit them or validate real risk. An external penetration test includes manual testing, active exploitation, OSINT gathering, password attacks, and a full analysis of what an attacker could actually accomplish. Vulnerability scans produce false positives and can miss complex issues or business risks, while penetration tests validate real risk.
This depends on the service providers you use and the contracts you have with them. We have some clients who like to start the test without notifying their MSSP or SOC to ensure alerts are properly working, and others that notify them well in advanced. During our kickoff call, which happens the week prior to the penetration test, your lead engineer will talk through this with you and cover any concerns you might have.
While we can never say never, in the vast majority of cases, no. Simply put, these systems are on the Internet and are being scanned constantly, so if any of the testing would cause a problem, you likely would have already experienced them. Additionally, our experienced testers take precautions to avoid service disruption. Flag any fragile or legacy systems during the kick-off call so the team can handle them appropriately.
Partially. An external penetration test includes unauthenticated web application testing. It does not include authenticated testing, role-based access control evaluation, or the comprehensive OWASP Top 10 coverage of a dedicated web application penetration test.
At a company level, there really is only one organizational penetration testing certification, and that is CREST. However, as this is a trust relationship, evaluate whether the penetration test company is securing your data properly with something like a SOC 2 Type II certification. For the penetration testers themselves, look for industry penetration testing certifications that include practical exams such as OSCP, CRTO, PNPT, etc. These reflect demonstrated, hands-on competence rather than just exam knowledge.
Following the penetration test you will receive three reports. The first is an executive summary that covers the areas you performed well, areas we recommend for improvement, and a detailed attack walkthrough showing how we gained access. Second, you will get a technical findings report that will detail every finding, where we found it, and how to fix it. Finally, we optionally provide a certification letter, which is meant for you to provide to third parties to demonstrate you had a penetration test performed. Here is a video that goes over all the reports.
Yes, for many frameworks. PCI DSS explicitly requires external penetration testing at least annually and after significant infrastructure changes. FedRAMP, CMMC Level 2+, and NIST 800-53 also include penetration testing requirements. HIPAA and ISO 27001 strongly imply it, and the FTC Safeguards Rule now explicitly requires it for the financial institutions it covers.
Confirm your backups are current, document any fragile or legacy systems on your perimeter, notify your IT and security team and any monitoring providers, and ensure a point of contact is available during testing. Do not harden your environment beforehand as the goal is to assess your real-world security posture.
The cost of an external penetration test is primarily driven by the time a qualified engineer spends evaluating your environment. The number of IP addresses on your Internet perimeter with at least one open port accepting connections, is the biggest single cost driver. For smaller organizations this can cost around $5,000 but for larger organizations with many locations this can cost significantly more.
Ready to Get Started?
Triaxiom Security performs external penetration tests for organizations of all sizes from small businesses with a handful of Internet-facing systems to large enterprises with complex perimeter environments. Our engineers hold industry-leading certifications and have performed hundreds of external penetration tests across a wide range of industries and compliance frameworks.
If you have questions about scoping, pricing, or how an external penetration test fits into your broader security program, contact us today! We are happy to discuss your specific situation and help you make the most informed decision for your organization.
