Your Introduction to Assumed Breach Penetration Testing

Assumed Breach Penetration Testing (ABPT) is a specialized security assessment that starts from the premise that an attacker has already successfully bypassed perimeter defenses. Instead of focusing on how a threat actor gains initial access, like with traditional external or internal penetration tests, the assumed breach model begins after that point, simulating an attacker who already has a foothold inside the network.

This method mirrors the real-world tactics of sophisticated adversaries such as Advanced Persistent Threat (APT) groups, ransomware operators, or insider threats who can move laterally across systems, escalate privileges, and extract sensitive data once inside.

The Objectives of ABPT

The primary goal of assumed breach testing is to evaluate the following:

• Detection capabilities: How efficiently and thoroughly your security teams can identify and respond to unauthorized activity post-compromise.

• Lateral movement paths: Whether threat actors can move from the compromised entry point to other high-value assets (such as, but not limited to, domain controllers and sensitive databases).

• Privilege escalation weaknesses: Whether misconfigurations or unpatched vulnerabilities allow attackers to gain higher-level access.

• Data exfiltration risks: How easily threat actors could extract sensitive information without being noticed.

This approach is especially valuable for organizations that already have mature security controls and want to test the effectiveness of their defense-in-depth, SIEM, and EDR solutions under realistic breach scenarios.

How Assumed Breach Penetration Testing Compares to "Traditional" Network Penetration Testing

Assumed breach engagements are often customized to reflect a specific threat model. Common examples include:

• Compromised domain-joined workstation: Can the threat actor move laterally from an employee’s computer to the domain admin?

• Stolen credentials: What happens if a threat actor acquires valid (but limited) credentials via phishing?

• Compromised cloud environment: Can lateral movement be performed in a hybrid or multi-cloud setting?

• Insider threat simulation: Can a malicious insider exfiltrate data from finance or HR systems undetected?

When Should Your Organization Consider Assumed Breach Testing?

Assumed breach testing is best suited for organizations that have already conducted traditional penetration tests( both external and internal) and are looking to go beyond surface-level vulnerabilities. It is particularly valuable when the objective is to evaluate how security controls perform after an initial breach has occurred. For organizations seeking a deeper understanding of how far an attacker could move laterally or escalate privileges once inside, this type of engagement provides more realistic and impactful insights than conventional testing alone.

It's also frequently leveraged for environments with a mature Security Operations Center (SOC) or a managed detection and response (MDR) service in place. In these scenarios, assumed breach testing allows teams to validate whether detection technologies are properly tuned and whether alerts are being generated and escalated quickly and thoroughly: it helps organizations move beyond simply having tools in place, toward ensuring those tools can detect stealthy adversarial behavior in practice.

Companies preparing for ransomware readiness assessments, cyber incident simulations, or tabletop exercises will also benefit from assumed breach engagements. These tests introduce a real-world element to simulated events, showing not only how an attacker might gain access, but how far they could go if left unchecked, providing data that can feed directly into risk modeling and crisis planning.

Lastly, assumed breach testing is a powerful tool for demonstrating security resilience to stakeholders such as executive leadership, boards of directors, and auditors. It delivers tangible evidence of security posture beyond checklists and compliance, aligning cybersecurity investments with measurable outcomes that matter to business continuity and reputation.

What Are the Tools and Tactics Used in ABPT?

Assumed breach tests leverage Red Teaming tools and tactics that mimic advanced adversaries. These commonly include:

• Cobalt Strike or similar C2 frameworks

• Mimikatz for credential harvesting

• BloodHound for Active Directory path analysis

• Living-off-the-land binaries (LOLBins) to evade detection

• Custom payloads designed to avoid triggering antivirus or EDR

Defensive measures such as EDR/XDR telemetry, Windows Event Logging, and SIEM correlation rules are often tested during the engagement.

At Packetlabs, we model the risk of an attacker breaching your IT environment and then pivoting into operational technology (OT) systems, testing your segmentation, monitoring, and access controls along the way.

Conclusion

The final report from an assumed breach test typically includes:

• A step-by-step narrative of the simulated attacker’s path

• The showcasing of successful exploitation or privilege escalation

• Remediation recommendations to close gaps in lateral movement, privilege access, and response time

• Mapping to MITRE ATT&CK techniques for alignment with known adversarial behaviors

• A collaborative debrief with internal security teams to share lessons learned and top takeaways

When Assumed Breach Penetration Testing with Packetlabs, we focus on the paths that matter... straight to your "crown jewels." By eliminating audit noise, we test your detection, response, and containment where it counts the most, delivering faster, more cost-effective engagements.