Why Assumed Breach Scenarios Are Crucial in Today’s Security Landscape 

The castle-and-moat model is simple: build strong perimeter defences, trust everything inside. Firewalls, VPNs, and access controls create a protective shell, and the business assumes safety within that shell.

But today’s attackers don’t always need to scale the walls. They can:

• Phish an employee and hijack a laptop

• Exploit a misconfigured cloud asset

• Use stolen credentials purchased on the dark web

• Piggyback in through a compromised third-party vendor

Once inside, attackers move laterally, escalate privileges, and seek valuable targets like domain controllers, email servers, and customer data.

If your security strategy only focuses on the outer defences, you’re leaving the inside wide open.

An assumed breach test begins with a simple but powerful assumption: that the attacker is already inside.

Rather than focusing on breaching your perimeter, we simulate a scenario where that part has already happened, perhaps through a successful phishing email, a stolen credential, or a vulnerable third-party vendor. Our red team is granted initial access to your environment, just as a real-world attacker might gain through stealthy, low friction means.

From there, we operate under the conditions of a post-compromise intrusion, using realistic tactics to mimic what an adversary would actually do inside your network. This includes:

• Moving laterally across systems and segments to explore network pathways

• Elevating privileges to gain administrative access or reach high-value targets

• Enumerating your environment, mapping out assets, user accounts, and infrastructure

• Identifying and exfiltrating critical data, such as PII, intellectual property, or authentication tokens

• Evading detection to assess how quietly an attacker could operate

• Triggering response protocols - intentionally or through stealth, to assess how your blue team reacts

This isn’t just a theoretical exercise or a box-ticking audit. It’s a real-world simulation of the worst-case scenario, designed to expose weaknesses that only show up under pressure. Crucially, it evaluates not only your technical controls like EDR, SIEM, and segmentation - but also your people and processes.

Are your detection tools noisy but ineffective? Does your SOC triage the right alerts? Do internal teams know how to escalate or contain a breach in progress?

An assumed breach test reveals all of this and more, without needing to break through the front gate. Because if attackers can get in anyway, the real question becomes: how far can they go before you notice?

Here’s why assumed breach scenarios are a crucial part of a modern security strategy:

1. Attackers Are Already Inside - Statistically Speaking

The rise of remote work, cloud adoption, and supply chain complexity means that perimeter breaches are increasingly likely. Studies show that many organisations have already experienced a compromise, they just don’t know it yet.

2. Most Breaches Start with Human Error

From weak passwords to phishing, humans are the easiest “exploit.” An assumed breach test accepts this reality, and shifts focus from prevention to detection and response.

3. You Learn How Attacks Really Play Out

Penetration testing often stops short of full exploitation. Assumed breach tests go deeper, mirroring what real attackers would do once inside and highlighting what they’d find valuable.

4. You Validate Internal Defences

EDR, SIEM, and SOC investments mean nothing if they’re not catching intrusions. An assumed breach test gives you real feedback on what your tools missed, what your team detected, and how quickly they responded.

5. It Supports Compliance and Cyber Maturity

Frameworks like MITRE ATT&CK, NIST, and DORA (for financial firms) all emphasise testing incident response capabilities, not just perimeter security. Assumed breach exercises provide auditable evidence that you’re taking proactive steps to test resilience.

Assumed breach is a natural fit for threat-led penetration testing, especially under frameworks like CBEST, TIBER-EU, and GBEST. These exercises are based on real-world threat intelligence tailored to your sector and assets.

Rather than guessing what an attacker might do, threat-led testing focuses on what they actually do and assumed breach is a powerful way to validate your defences against these known tactics.

In a black team engagement, even internal security teams are unaware a test is taking place. Assumed breach scenarios are ideal here as they simulate a silent intruder inside the network, moving like a real threat actor, and testing your team's blind spots.

Our Black Teaming services combine red teaming, assumed breach, and stealth techniques to measure detection capabilities without alerting the blue team.

To get maximum value from your assumed breach engagement, it’s important to treat it as more than just a red team exercise. With the right setup and follow-through, it becomes a powerful way to strengthen your entire security posture.

• Clear Objectives: Define what success looks like, whether it’s reaching the domain controller, exfiltrating fake PII, or testing SOC response.

• Controlled Access: Work with your red team to define realistic initial access, such as a compromised laptop or cloud admin account.

• Monitoring and Logging Review: Assess whether logs were generated, correlated, and escalated appropriately.

• Debrief and Remediation: Use the findings to improve detection rules, segmentation, access controls, and team workflows.

By treating your assumed breach test as both a technical challenge and an operational stress test, you gain a far clearer picture of your organisation’s resilience under real-world conditions.