The Challenge
Your firewall blocks external attacks, and your IDS monitors traffic at the boundary. But what happens when someone's already inside your network?
This question confronts every fraud risk manager protecting cardholder data environments. The challenge isn't hypothetical. Social engineering can get an attacker past your perimeter. Phishing can put credentials in the wrong hands. A compromised vendor account opens a door. Once inside, how quickly can they move laterally? How long before they reach your CDE?
Penetration testing teams regularly encounter organizations that invest heavily in perimeter defenses but lack visibility into their internal security posture. Their testing methodology addresses a specific gap: what can an adversary accomplish after initial access?
The Environment and Constraints
Internal penetration tests operate under different constraints than external assessments. The scope must be carefully defined upfront. Which network segments are in scope? Are testers simulating a compromised employee account, a contractor with VPN access, or an attacker who's breached a workstation?
The testing team uses three approaches:
Black Box testing provides no internal knowledge. Testers start as an outsider would, with no network maps or credentials. This method is thorough but time-consuming.
White Box testing gives testers full access to network schematics, IP addresses, and source code. It's faster and more comprehensive but doesn't simulate a realistic attack path.
Gray Box testing positions the tester as a privileged user. This "live" approach balances realism with efficiency.
For compliance-driven organizations, constraints include maintaining business continuity during testing and ensuring the test itself doesn't trigger false positives in fraud detection systems or create audit trail gaps.
The Approach Taken
VikingCloud's methodology breaks internal testing into six phases, each designed to answer specific questions fraud risk managers need answered.
Planning and Preparation establishes what you're actually testing. Is this about password strength across your payment operations team? Access controls around your transaction database? The ability to escalate privileges from a customer service account to an administrator role?
Information Gathering maps the internal network. Testers identify systems, services, and data flows. In payment environments, this phase reveals how cardholder data moves between authorization systems, settlement processes, and reporting databases.
Vulnerability Assessment identifies weaknesses before exploitation. Testers document poor encryption practices, single-factor authentication on sensitive systems, outdated software in the CDE, and misconfigurations that create unintended access paths.
The techniques used during assessment mirror real attacks: brute-force password attacks, privilege escalation attempts, database control testing, man-in-the-middle attacks, communication eavesdropping through protocol poisoning, port scanning, and testing both hardware vulnerabilities (routers, IoT devices, workstations, printers) and software vulnerabilities (operating systems, outdated programs).
Exploitation tests how far an attacker can go. Can they access unencrypted PANs in application logs? Move from a compromised workstation to a database server? Extract encryption keys from memory? The goal isn't just to find vulnerabilities but to understand their business impact.
Documentation captures what worked and what failed. Every vulnerability gets recorded with its severity, exploitability, and potential impact on your fraud controls and compliance posture.
Vulnerability Resolution translates findings into actionable remediation. This isn't a generic report. It's a prioritized action plan based on what testers actually achieved during exploitation.
Results and Metrics
Internal penetration tests reveal specific security gaps that external testing misses. Testers analyzing potential threats through social engineering, password theft, and phishing consistently discover:
- Poor encryption practices that leave cardholder data readable in memory or logs
- Weaknesses in access and identity controls that allow lateral movement
- Low password security, including single-factor authentication on systems handling sensitive data
- Outdated software or security protocols in production environments
- Accidental system misconfigurations that create unintended trust relationships
- Evidence of intentional internal damage or policy violations
The documentation phase produces measurable outcomes: time to initial compromise, number of systems accessed, sensitivity of data extracted, and persistence mechanisms established. These metrics help fraud risk managers quantify internal risk exposure.
What They Would Do Differently
Organizations that run internal penetration tests for the first time often discover they've been testing the wrong things. They've focused on perimeter security while internal segmentation remained weak. They've invested in endpoint detection but haven't tested whether those controls actually prevent lateral movement.
The testing approach itself evolves. Pure Black Box testing, while realistic, consumes time without providing the comprehensive coverage compliance frameworks require. Most organizations shift toward Gray Box testing that simulates a compromised insider while maintaining testing efficiency.
Integration with regular security audits improves over time. Initial tests run as one-time projects. Mature programs incorporate internal penetration testing into quarterly or semi-annual security reviews, with each test building on previous findings.
The scope definition becomes more precise. Early tests try to cover everything. Later tests focus on specific attack paths: "Can someone in customer service access cardholder data they shouldn't see?" or "If our payment gateway is compromised, what else can an attacker reach?"
Takeaways for Your Team
Internal penetration testing is essential if you're managing fraud risk in a payment environment. PCI DSS requires testing of security controls, and internal testing validates whether those controls actually work under adversarial conditions.
Run both internal and external tests. External testing shows how attackers get in. Internal testing shows what they can do once they're in. Neither perspective alone gives you the complete picture.
Define scope based on your threat model. If your biggest risk is compromised customer service accounts, test from that starting point. If you're concerned about vendor access, simulate that scenario.
Use the findings to drive specific improvements. Generic recommendations don't reduce fraud risk. Prioritize based on what testers actually accomplished: which systems they compromised, what data they accessed, how long it took.
Don't assume your controls work until you test them under realistic conditions. Your firewall might be excellent. Your internal segmentation might be nonexistent. You won't know until someone tries to move laterally through your network with adversarial intent.
The gap between perimeter security and internal security posture creates the conditions for fraud. Internal penetration testing exposes that gap before an attacker exploits it.
