Interface Risk - The Overlooked Frontier in Cybersecurity

Examples of Interface Risk - Where Exposure Lives

Executive Summary

In today’s hyper-connected digital ecosystems, most cybersecurity frameworks focus on endpoints, users, and internal systems. Yet, a disproportionately large number of cyber incidents originate not from within these domains, but at the boundaries between them. We call these vulnerable boundaries "interfaces," and the risks that emerge from them, "Interface Risks."

This article introduces the concept of Interface Risks as a critical, yet under-recognised, category of cybersecurity risk. It proposes a structured methodology for analysing and mitigating risks at points of interaction between systems, processes, organisations, and people.

1. Introduction

As digital transformation drives deeper integration of systems, processes, and vendors, the number of interfaces grows exponentially. Each new interface introduces potential security blind spots. Examples include:

• Man-in-the-middle (MITM) attacks between user and server.

• Misconfigured APIs between applications.

• Process gaps between departments leading to fraud.

• Misunderstood contractual responsibilities between vendor and client.

Cybersecurity professionals often view systems as discrete entities. However, most compromises today exploit assumptions, inconsistencies, or gaps at the interface between these systems.

2. Defining Interface Risk

An Interface Risk arises where two or more systems (human, digital, or organisational) interact, and there is:

• Ambiguity in ownership or responsibility.

• Inconsistency in access control, validation, or security controls.

• A breakdown in trust assumptions.

• A lack of monitoring or enforcement at the interface.

Interface Risks manifest in various forms:

• Human-System Interfaces: Social engineering, misused credentials.

• System-System Interfaces: API misuse, protocol vulnerabilities.

• Network Interfaces: MITM, DNS spoofing, lateral movement.

• Organisational Interfaces: Third-party breaches, unclear accountability.

• Process Interfaces: Manual workarounds, broken handovers.

3. The Interface Risk Analysis (IRA) Methodology

To manage Interface Risk, we propose the Interface Risk Analysis (IRA) methodology:

Step 1: Interface Inventory

Using brainstorming and various recording methods e.g. white-boarding

• Map out all interfaces between systems, users, and processes.

• Use data flow diagrams, BPMN, and architectural schematics.

Step 2: Interface Profiling

Define each interface’s purpose, data exchanged, directionality, trust model, access control, and visibility.

Step 3: Risk Identification

Apply STRIDE and zero trust lenses to each interface:

• Is identity authenticated?

• Are permissions enforced?

• Can data be altered in transit?

• Is this a point of failure or denial?

Step 4: Prioritisation

Score interfaces by:

• Criticality to business.

• Sensitivity of data.

• Exposure level.

• Ownership clarity.

Step 5: Control Recommendations

Apply technical and process controls:

• Encryption, auth hardening, logging.

• Clear interface ownership.

• Independent validation and reconciliation.

4. Use Case Examples

4.1 SolarWinds Supply Chain Attack An attacker exploited the interface between a vendor’s update mechanism and thousands of client systems, leveraging trust without verification.

4.2 OAuth Misuse in Consumer Apps Applications assumed OAuth tokens granted limited access. Attackers used them for privilege escalation due to poorly defined scopes.

4.3 Insider Fraud at Process Handover An employee manipulated a payment instruction during a poorly monitored manual handover between procurement and finance.

5. Strategic Implications

• For CISOs: Interface Risk frameworks help redefine the attack surface. Boards and regulators increasingly demand evidence of supply chain, process, and partner security—all of which are interfacial.
  

• For Regulators: Interface Risks underpin many breaches. Policies like DORA and NIS2 require cross-organisational risk management that aligns well with Interface Risk models.
  

• For Cybersecurity Vendors: A shift to interface-aware products (e.g., secure API gateways, cross-domain monitoring, identity validation tools) is needed.

6. The Path Forward

We recommend the following steps:

• Adopt Interface Risk as a formal category in risk registers.

• Integrate IRA methodology into threat modelling and architecture reviews.

• Develop "Golden Interface" registers to prioritise monitoring and control.

• Educate security professionals to think beyond system silos.

Conclusion

Interface Risk is not a new class of threat but a new way of understanding how vulnerabilities emerge in complex systems. By reorienting cybersecurity thinking towards interfaces, organisations can surface risks that previously remained hidden, and close the gaps where most breaches actually occur.