Attack Surface Management Series: Defining and Identifying Your Attack Surface

In today’s evolving threat landscape, understanding your attack surface is no longer optional, it’s foundational. Before you can defend your organization effectively, you need to know what you’re defending. That’s why the first step in any strong Attack Surface Management (ASM) program is clearly defining and identifying your attack surface.

But what exactly is an “attack surface”? Let’s break it down.

What Is an Attack Surface?

Think of your attack surface as the total collection of all the points in your environment where a threat actor could gain access to your systems, data, or services. These entry points can exist across your:

• Internal network and infrastructure
• Public-facing web applications and APIs
• Cloud assets and third-party services
• Endpoints and mobile devices
• Users and identity access points

In short, your attack surface is bigger than your firewall. It’s everything that could be touched, either intentionally or unintentionally, by someone trying to get in.

Why Is It Expanding?

Modern IT environments are dynamic. Cloud adoption, remote work, shadow IT, and third-party integrations have all contributed to the rapid expansion of most organizations’ attack surfaces. Even well-intentioned development practices, like spinning up a test environment or deploying a quick patch, can introduce new, untracked assets or vectors for malicious actors to gain access to your environment.

This expansion is why traditional perimeter-based security models no longer cut it. The perimeter is porous and constantly shifting, and you need visibility across all layers of your organization to stay ahead.

Types of Assets That Make Up the Attack Surface

Here’s a high-level view of what typically comprises an organization’s attack surface:

• Known assets: Systems and services your IT and security teams are actively managing.
• Unknown or shadow assets: Instances like forgotten web applications, orphaned cloud services, or test environments that didn’t get decommissioned.
• Third-party assets: SaaS tools, APIs, and vendor-hosted platforms that your team relies on but may not directly control.
• Misconfigured assets: Assets that may be known but are insecure due to improper setup or outdated patches.

How to Identify Your Attack Surface

Start by creating an inventory… but not just of what you think you have. Use tools and services that can scan, discover, and classify assets both inside and outside your environment. Include:

• External scans to detect what’s publicly accessible
• Internal asset discovery tools for endpoints, servers, and network devices
• Cloud inventory tools to map cloud-native resources
• Identity and access data to understand user exposure

This discovery phase should be ongoing, not a one-time effort. (We’ll talk more about that in the second blog of this series when we get into continuous monitoring and prioritization.)

The Risk of the Unknown

One of the most dangerous aspects of the attack surface is what you don’t know about. Shadow IT, expired domains, and unused services can create blind spots that threat actors are actively looking to exploit. Simply put, you can’t secure what you don’t see.

That’s why defining your attack surface isn’t just a technical task, it’s a strategic initiative. It requires collaboration between IT, security, DevOps, and even procurement or legal, especially when it comes to managing third-party risks.

Setting the Foundation for What Comes Next

Defining and identifying your attack surface lays the groundwork for everything else in your cybersecurity program. In our next blog, we’ll explore how to continuously monitor these assets, keep your asset map up to date, and prioritize the vulnerabilities that matter most.

Because knowing what’s exposed is only the beginning and understanding how to act on that information is what turns insight into impact.

Jimmy Armour is a cybersecurity and compliance professional specializing in NIST, SOC 2, and CIS GRC frameworks. As a Practice Lead, he guides cross-functional teams to streamline audit processes, strengthen security posture, and meet rigorous regulatory requirements—always staying on the cutting edge of emerging cybersecurity trends.

Outside of his professional pursuits, Jimmy is deeply involved in Harrisburg Young Professionals Sports—playing kickball, dodgeball, and bowling—while also participating in the 247Kickball leagues. Some years even take him to national kickball tournaments. All of which are experiences he finds mirrors the same camaraderie and teamwork that drive his success in the workplace.