Assumed Breach: Testing Your Defenses from the Inside Out

Introduction: The Inevitable Truth – A Breach is Not “If,” But “When”

In our previous deep dive, “The Insider Threat Unmasked: Rogue Device Testing with Kali Linux (No Credentials)“, we explored the critical vulnerabilities exposed when an attacker gains physical access to your internal network, even without credentials. That scenario highlights the importance of foundational internal controls. But what happens once those initial, often robust, perimeter defenses are bypassed? What if an attacker successfully phishing an employee, or a piece of malware slips through your email gateway?

The modern cybersecurity paradigm acknowledges a sobering truth: a breach is less about “if” and more about “when.” Sophisticated threat actors, whether nation-states, organized crime, or determined individuals, are increasingly capable of finding novel ways to penetrate even the most well-defended perimeters. This reality has given rise to the Assumed Breach testing methodology, a pragmatic and highly effective approach to internal penetration testing.

This second post in our series will take you inside the Assumed Breach test. We’ll explore how cybersecurity experts deliberately bypass the perimeter to simulate an attacker who has already gained an initial foothold. By operating from the perspective of a standard breached account and machine, this test reveals exactly how resilient your internal network is to lateral movement, privilege escalation, and data exfiltration, providing invaluable insights into your incident detection and response capabilities. Prepare to confront the internal realities of your security posture.

The Inevitable Truth: Why “Assumed Breach”?

The shift towards an “assumed breach” mentality is not a sign of surrender, but rather a strategic evolution in cybersecurity. For decades, the focus was predominantly on building an impenetrable “castle and moat” defense, concentrating resources on stopping attackers at the perimeter. While perimeter security remains vital, the escalating sophistication of cyberattacks, coupled with the increasing complexity of enterprise networks (cloud integrations, remote work, BYOD), has rendered the “unbreachable” perimeter an illusion.

Here’s why the “assumed breach” philosophy has become indispensable:

1. 1. Sophisticated Initial Access: Attackers employ advanced techniques like zero-day exploits, highly convincing spear-phishing campaigns, supply chain attacks (as seen with SolarWinds), and social engineering tactics that can bypass even cutting-edge perimeter defenses. It’s difficult to stop every single attempt.

1. 1. Insider Threats: Whether malicious or unintentional, insiders pose a significant risk. An assumed breach test can simulate a compromised insider account, focusing on the damage they could inflict from within.

1. 1. Third-Party Risk: Compromise of a trusted third-party vendor or partner can provide a direct pathway into your network.

1. 1. Focus on Internal Resilience: Rather than expending all resources on preventing entry (which is never 100% guaranteed), the “assumed breach” model dedicates resources to identifying how quickly an attacker can achieve their objectives once inside, and critically, how effectively you can detect and contain them.

1. Maximizing Testing Efficiency: By starting from an internal foothold, penetration testers can immediately dive into the most complex and critical phases of an internal attack – lateral movement, privilege escalation, and data exfiltration – without spending valuable time trying to breach the external defenses. This ensures the testing budget is utilized where it matters most: validating internal controls and incident response.

In essence, “assumed breach” acknowledges that initial compromise is a real possibility and shifts the focus to minimizing the impact and preventing significant data loss or system disruption. It forces organizations to build and test robust internal detection, containment, and response mechanisms, fundamentally strengthening their overall security posture.

The Assumed Breach Scenario: A Realistic Starting Point

An Assumed Breach test is deliberately designed to mimic the starting point of a real-world attacker who has successfully gained initial access. The penetration testing team doesn’t try to break through your firewalls or exploit your external web applications. Instead, they are granted a pre-defined level of access, making the engagement highly efficient and focused.

Common starting points for an Assumed Breach scenario include:

• • Compromised Standard User Account and Machine: This is the most common and realistic scenario. The testing team is provided with:
    
    • • Credentials for a standard, non-privileged domain user. This simulates a successful phishing attack where an employee’s credentials were stolen.
    • • Access to a typical employee workstation. This simulates a successful malware infection on an endpoint, which then acts as the initial pivot point for the attacker. The workstation might be physically separate or accessed via a secure remote desktop connection established by the client for the test.

• • Compromised Server: In some cases, the starting point might be access to a non-critical internal server with limited privileges, mimicking a scenario where a less critical system was initially exploited or misconfigured.

• Segmented Network Access: For testing network segmentation, the tester might be placed directly onto a specific internal network segment (e.g., a development network or IoT network) to see if they can break out into more sensitive zones.

The key here is that the starting access is not administrative and the initial machine is not a critical server. It represents a typical entry point for an attacker aiming to expand their foothold and move towards high-value targets. This ensures the test accurately reflects the real challenges your internal defenses face once an initial compromise has occurred.

Key Phases and Tactics of an Assumed Breach Test

Once the initial access is granted, the Assumed Breach test unfolds much like a real adversary’s post-compromise activities. The Red Team or penetration testers will systematically attempt to escalate privileges, move laterally, collect data, and establish persistence, leveraging a variety of sophisticated techniques. The MITRE ATT&CK® framework is often used by testers to map their activities to known adversary tactics, ensuring comprehensive coverage and clear reporting.

1. 1. Internal Reconnaissance & Mapping:
      
      • • Objective: Understand the internal network topology, identify critical assets, discover active users and groups, and locate sensitive data.
      • • Tactics:
          
          • • Network Scanning (Internal): Using tools like Nmap or Masscan to scan internal IP ranges for open ports and services, but often doing so stealthily to avoid detection by internal network security monitoring.
          • • Active Directory Enumeration: Querying Active Directory (AD) for information on users, groups, computers, domain controllers, trusts, and policies. Tools like BloodHound, ADExplorer, AdFind are common here. This maps potential attack paths to high-value targets.
          • • Share Enumeration: Discovering network shares (SMB, NFS) and attempting to access them for sensitive documents or configuration files.
          • • DNS Reconnaissance: Querying internal DNS servers to identify internal hostnames and services.
          • • Cloud Enumeration (Hybrid Environments): If the network is hybrid, attempting to enumerate connected Azure/AWS/GCP resources from the internal network.

1. 1. Privilege Escalation:
      
      • • Objective: Gain higher levels of access on the initial compromised machine or other systems (e.g., local administrator, system, or domain administrator).
      • • Tactics:
          
          • • Local Privilege Escalation (LPE): Exploiting vulnerabilities in the operating system kernel, misconfigured services, insecure file permissions, or outdated software on the initial workstation to gain local administrator rights.
          • • Domain Privilege Escalation: Leveraging weaknesses in Active Directory (e.g., Kerberoasting, AS-REP Roasting, Pass-the-Hash/Ticket, exploiting GPOs, weak ACLs) to gain domain administrator credentials. This is often the ultimate goal for full network control.
          • • Credential Dumping: Extracting credentials (hashes or plaintext) from memory (e.g., using Mimikatz), registry, or configuration files from compromised systems.

1. 1. Lateral Movement:
      
      • • Objective: Move from the initial compromised system to other machines, servers, or critical assets within the network.
      • • Tactics:
          
          • • Pass-the-Hash/Ticket: Using stolen credential hashes or Kerberos tickets to authenticate to other systems without needing the plaintext password.
          • • PsExec/WMI/WinRM: Using legitimate Windows administration tools to execute commands remotely on other systems using compromised credentials.
          • • SSH/RDP Abuse: Leveraging stolen SSH keys or RDP credentials to access other machines.
          • • Exploiting Internal Services: Leveraging vulnerabilities in internal web applications, databases, or other services to gain access to their underlying servers.
          • • VPN/Network Access: If internal VPNs or jump boxes are poorly secured, using them to reach segmented networks.

1. 1. Persistence Mechanisms:
      
      • • Objective: Ensure continued access to the compromised environment even if initial access methods are detected or systems are rebooted.
      • • Tactics:
          
          • • Backdoors: Installing hidden backdoors (e.g., modifying startup scripts, creating new user accounts, scheduled tasks, registry modifications).
          • • C2 (Command and Control) Channels: Establishing covert communication channels that blend in with normal network traffic (e.g., DNS tunneling, HTTP/S beacons) to maintain remote control over compromised systems and exfiltrate data without detection. This is crucial for stealth.

1. 1. Data Collection & Exfiltration:
      
      • • Objective: Identify, access, and exfiltrate sensitive data as defined in the engagement’s objectives (e.g., customer PII, intellectual property, financial records).
      • • Tactics:
          
          • • Searching File Shares/Databases: Systematically searching for sensitive documents, databases, or configuration files.
          • • DLP Bypass: Attempting to bypass Data Loss Prevention (DLP) solutions using various techniques (e.g., encrypting data, using unusual protocols, fragmenting data, leveraging cloud storage services).
          • • Covert Channel Exfiltration: Using the established C2 channels or other stealthy methods to transmit collected data out of the network.

By meticulously executing these phases, an Assumed Breach test provides a holistic and dynamic view of your internal security posture from the perspective of an attacker already operating within your environment.

What Does Assumed Breach Testing Uncover?

The insights gained from an Assumed Breach test are invaluable because they highlight real-world weaknesses that traditional, external-focused tests might miss. These engagements often uncover:

• • Weak Internal Segmentation: Many organizations have “flat” internal networks, meaning once an attacker is in, they can move almost anywhere. Assumed Breach tests expose these weaknesses, showing how easily an attacker can pivot from a low-priority workstation to critical production servers or the Active Directory domain controller.

• • Ineffective Internal Detection Capabilities: A key outcome is discovering whether your Security Operations Center (SOC) or security monitoring tools can actually detect the lateral movement, privilege escalation, and data exfiltration attempts occurring inside your network. Many organizations focus heavily on perimeter alerts but have poor visibility into internal malicious activity.

• • Poor Incident Response Effectiveness: The test acts as a realistic drill. It reveals if your incident response plan can effectively contain and eradicate a threat that is already present and moving laterally within your environment. It exposes gaps in communication, tooling, and procedural execution under pressure.

• • Over-Privileged Accounts and Systems: Testers often find that users and services have far more permissions than necessary, providing easy avenues for privilege escalation. Misconfigured systems with default credentials or weak security settings are also frequently discovered.

• • Unmonitored Critical Assets: High-value assets (e.g., databases, intellectual property repositories, backup servers) are often poorly monitored internally, allowing attackers to access and exfiltrate data without triggering alerts.

• Human Factor Weaknesses (Internal): While initial social engineering might be external, internal social engineering (e.g., impersonating an IT help desk or colleague within an internal chat system) can also be used during an assumed breach to gather more information or credentials.

The findings from an Assumed Breach test provide a concrete, actionable roadmap for strengthening your internal defenses, prioritizing resources on the most impactful remediation efforts.

Benefits of Assumed Breach Testing

Embracing the Assumed Breach methodology delivers critical advantages for your cybersecurity strategy:

• • Realistic Assessment of Internal Resilience: Provides a true measure of your ability to withstand an internal attack, identifying precisely where your defenses might crumble once an attacker is inside.

• • Validates Internal Controls and Layered Defenses: Confirms whether your internal firewalls, network segmentation, Endpoint Detection and Response (EDR) solutions, Identity and Access Management (IAM) policies, and other internal controls are actually effective.

• • Optimizes Incident Response: Acts as an invaluable “live fire” exercise for your Blue Team, allowing them to practice detection, containment, and eradication under realistic conditions, leading to refined playbooks and faster response times during a real incident.

• • Prioritizes Remediation Efforts: Highlights the most critical internal weaknesses that lead to the highest business risk, allowing for strategic resource allocation.

• • Identifies Lateral Movement Paths to “Crown Jewels”: Clearly maps the routes an attacker could take from a standard workstation to your most sensitive data or critical systems.

• Cost-Effective Deep Dive: By bypassing perimeter testing, it allows for a more efficient and focused examination of internal vulnerabilities, maximizing the value of the testing budget.

Conclusion: Fortifying Your Inner Sanctum

In today’s threat landscape, assuming that your perimeter will always hold is a dangerous gamble. The Assumed Breach testing methodology acknowledges this reality and shifts the focus to what matters most: your ability to detect, contain, and recover from an internal compromise. By simulating an attacker already within your network, organizations gain unparalleled insights into their true internal resilience.

This isn’t about fear-mongering; it’s about pragmatic preparation. Understanding how far an attacker can go once they’ve slipped past your outer defenses is crucial for building a truly robust security posture. For advanced, objective-driven internal penetration testing and adversarial simulations, consider partnering with leading experts like Adversim, a Las Vegas-based cybersecurity consulting firm renowned for their comprehensive approach to uncovering and addressing internal security gaps.

In our next post, Blog Post 3: Compliance-Driven Internal Penetration Testing: PCI DSS and Beyond, we’ll delve into how internal penetration testing is not just a best practice, but a mandatory requirement for critical compliance frameworks, ensuring you meet regulatory obligations while genuinely enhancing your security.