Cyber threats can be both external and internal. In fact, 65% of the data breaches involved internal actors, while external parties caused 83%. This also shows that most of the data breaches involve both types of attack surfaces.
External assets are visible to any internet user, while internal assets are supposed to be protected behind firewalls. Both surfaces can harbor vulnerabilities, have unique threat vectors and require distinct strategies.
But that’s not the only difference between them.
What Is an Attack Surface?
An attack surface is the total number of points in your organization where unauthorized users can try to gain access to your systems or data.
What Is Internal Attack Surface Management (IASM)?
Internal Attack Surface Management (IASM) refers to the process of identifying, monitoring, and reducing risks related to assets and user activities inside your organization’s network within the firewall.
The internal attack surface includes everything used or accessed by employees, third-party contractors, or internal systems. In fact, 83% of organizations reported at least one insider attack in 2024, according to IBM.
The components included in the internal attack surface are:
- User devices, workstations and laptops
- Internal applications
- File shares and databases
- Network drives
- Privileged user accounts
Risks Involved
The biggest risks for internal attack surface management are insider threats, lateral movement by attackers, unauthorized access, and misuse of privileged access.
For instance, a successful phishing email can compromise a single employee, but that one breach can lead to initial access for lateral movement or delivery of a malicious payload that can spread across systems if internal defenses are weak.
Learn more about FortifyData’s agent-less internal scanning.
What Is External Attack Surface Management (EASM)?
External Attack Surface Management (EASM) is the practice of discovering, monitoring, and securing all of your organization’s internet-facing assets.
These are the systems and services visible to attackers without needing credentials or internal access. In a 2025 survey by TrendMicro they reported that 74% have experienced security incidents due to unknown or unmanaged assets and that over half (55%) of the respondents said they have no processes in place to do so [attack surface management] continuously
These assets form your digital perimeter and include:
- Domains and subdomains
- Cloud infrastructure (e.g., AWS, Azure, GCP)
- Public APIs
- Web applications
- SaaS accounts
- Exposed databases or services
Key Risks
Issues and risks with external surfaces come from what you don’t know exists. These overlooked assets are frequently targeted with automated scans and opportunistic exploits. Shadow IT, and now Shadow AI, misconfigured cloud services, expired SSL certificates, and forgotten subdomains are all common entry points for attackers.
Key Differences Between Internal and External Attack Surface Management
While both types of Attack Surface Management aim to reduce cyber risk by identifying and protecting digital assets, they operate in very different environments.
Here’s how they compare:
| Internal Attack Surface Management (IASM) | External Attack Surface Management (EASM) | |
| Visibility | Focuses on internal systems and assets behind the firewall | Focuses on internet-facing assets exposed to the public |
| Threat Type | Insider threats, privilege misuse, and phishing | External attackers, automated scans, and shadow IT exploitation |
| Detection Tools | Network monitoring, endpoint detection, and identity systems | Passive reconnaissance, EASM platforms, threat intelligence feed |
| Security Response | Access controls, segmentation, DSPM, and user behavior analysis | Asset discovery, misconfiguration fixes, and threat exposure management and remediation |
Why You Need Both for Complete Protection
Managing just your internal or external attack surface is no longer enough. Most modern breaches don’t stick to one side of the firewall; they move between both. The growing strategy of threat exposure management instills attack surface management at its core since threat exposures and vulnerabilities can be chained for an attack path that penetrates through external assets into internal assets.
That’s why combining IASM and EASM gives you the full defense picture.
Compliance and Audit Pressures
Regulations like GDPR, HIPAA, and CCPA, in addition to a growing number of cyber insurance providers, expect organizations to show clear steps for securing both internal and external systems. Auditors want proof of continuous monitoring.
In 2024, 46% of enterprises experienced audit delays and increased costs due to incomplete or inaccurate asset data, often tied to unmanaged exposure or lack of tracking.
If you’re only managing one side, you’re leaving blind spots that could lead to fines or worse, reputational damage after a breach.
Faster Detection, Better Outcomes
When External and Internal Attack Surface Management work together, your mean time to detect (MTTD) drops significantly. It’s also backed by a study by IBM, which showed that internal detection can decrease the lifecycle of a data breach by 61 days and save up to $1 million in costs.
EASM flags new internet-facing risks as they appear. IAM spots abnormal behavior inside your environment. Combined, they create a feedback loop that helps your security team respond faster, smarter, and with better context.
Take Control of Every Corner of Your Attack Surface
If you’re only focusing on internal systems and ignoring the cloud assets, forgotten APIs, or exposed subdomains, you’re leaving the equivalent of your front door wide open in a home security analogy.
However, you don’t need to choose between Internal and External Attack Surface Management. You need both and many attack surface providers have a platform that can accommodate both At FortifyData, we do exactly that. Our Attack Surface Management solution helps you monitor everything. This unified platform offers real-time visibility, contextual threat intelligence, and continuous monitoring across all environments.
Request a free attack surface assessment today!
FAQs
1. What is the difference between internal and external attack surfaces?
Internal attack surfaces include systems and users inside your network perimeter (like employee user devices and internal applications). Meanwhile, external attack surfaces are publicly accessible systems like websites, APIs, and cloud assets exposed to the internet.
2. Why can’t I rely on a firewall alone to protect my internal systems?
Firewalls block unauthorized access and malicious traffic but they can’t stop threats that originate internally. These include phishing, privilege misuse, or insider attacks. Internal attack surface management (IASM) is essential for visibility behind the firewall.
3. What is shadow IT, and why is it dangerous?
Shadow IT refers to software, devices, or cloud services used without IT’s knowledge or approval. These hidden assets often lack proper security, making them vulnerable entry points for attackers.
