What Is a Shadow API?

APIs have become the primary interface through which modern systems exchange data and execute business logic. As organizations adopt microservices, cloud native architectures, and automation driven workflows, the number of APIs operating in production environments continues to grow.

Industry research consistently indicates that API growth is outpacing visibility and governance. Gartner has repeatedly highlighted unmanaged and unknown APIs as a growing source of security exposure, particularly as enterprises rely on distributed teams and rapid delivery models. These conditions make it difficult to maintain an accurate understanding of which APIs are active at any given time.

IBM security research has shown that APIs are increasingly involved in data exposure incidents, not because APIs are inherently insecure, but because they often provide direct access to sensitive systems and data. When APIs operate outside expected controls, the impact of misconfiguration or misuse increases significantly.

Postman’s industry reports reflect similar trends from an operational perspective. API ownership is highly decentralized, with teams independently creating and modifying interfaces to meet product needs. In many organizations, there is no single authoritative source that reflects all APIs currently handling production traffic.

Shadow APIs emerge at the intersection of these trends. They are not the result of isolated failures or poor practices. They arise when the reality of API execution diverges from documented and governed assumptions. This divergence creates a class of risk that traditional security and governance models are not designed to address.

Why Shadow APIs Exist in Modern Enterprise Systems

Shadow APIs exist because modern software delivery prioritizes speed, autonomy, and scalability. Teams are empowered to design, deploy, and evolve APIs independently, often with minimal central coordination.

Microservices architectures distribute ownership across services and teams. Each service exposes interfaces to fulfill specific functions, and those interfaces evolve over time. As systems scale, maintaining a complete and current inventory of all APIs becomes increasingly difficult.

Continuous integration and continuous delivery pipelines further contribute to this condition. APIs can be deployed or modified multiple times per day. When governance and inventory updates are not embedded directly into delivery workflows, APIs may reach production without being registered or reviewed centrally.

Internal APIs may also become externally reachable due to network changes, cloud configuration drift, or integration requirements. APIs originally designed for internal consumption can unintentionally expand the attack surface when exposure assumptions change.

Partner and third party integrations introduce additional complexity. External services may expose or consume APIs that are not fully visible to internal security teams. Changes on either side of the integration can create new access paths without explicit approval or documentation.

Automation and AI driven systems add another dimension. These systems can generate API calls, orchestrate workflows, or expose dynamic interfaces at runtime. As their use increases, so does the number of APIs operating outside traditional governance processes.

Shadow APIs are therefore a predictable outcome of how modern systems are built and operated. Their existence reflects structural characteristics of enterprise software delivery rather than individual lapses in control.

What Is a Shadow API?

A shadow API is an API that exists and processes traffic in a production environment but operates outside documented, monitored, and governed security assumptions. The API may be unknown to central teams, excluded from formal inventories, or bypass established security controls.

Shadow APIs are defined by their operational status rather than their intent. They actively handle requests and responses, often performing meaningful business functions or accessing sensitive data. Their risk arises from the absence of consistent oversight, not from whether they were created deliberately or accidentally.

It is important to distinguish shadow APIs from related concepts. An undocumented API endpoint is a specific interface that lacks documentation. Shadow APIs are a broader category that includes undocumented endpoints but also encompasses APIs that bypass monitoring, gateways, or policy enforcement.

Zombie APIs typically refer to deprecated or unused interfaces that remain reachable. While zombie APIs may become shadow APIs if they handle traffic without oversight, not all shadow APIs are inactive or legacy. Many are actively used and evolve alongside documented services.

Rogue APIs imply malicious intent or unauthorized development. Shadow APIs do not require malicious intent. They emerge when APIs fall outside governance boundaries, even when created for legitimate business reasons.

A shadow API is therefore best understood as an interface that exists in the gap between how an organization believes its API surface is governed and how APIs actually operate in production.

How Shadow APIs Are Created in Production

Shadow APIs are created through common and often necessary engineering practices. They typically emerge through incremental change rather than through a single design decision or control failure.

Decentralized Service Ownership

In microservices and distributed architectures, teams own services independently and expose APIs to meet local product requirements. Ownership boundaries are fragmented, and no single team maintains a complete view of all interfaces operating across the environment. As services evolve, some APIs fall outside centralized governance and monitoring processes.

CI/CD Pipelines Without Embedded Governance

Continuous integration and continuous delivery pipelines enable rapid deployment of new endpoints and changes. When API registration, security review, and inventory updates are not enforced as part of these pipelines, APIs can reach production without being captured in authoritative records.

This gap is amplified in environments where deployment frequency is high and manual reviews cannot scale.

Feature Flags, Debug, and Administrative Endpoints

Feature flags and experimentation frameworks introduce conditional behavior that may expose temporary endpoints. Debug and administrative interfaces are often created to support development or operations and may bypass standard security controls. When these interfaces remain enabled in production, they become shadow APIs.

Deprecated and Legacy Interfaces

APIs are frequently deprecated to support new versions or functionality. However, removal is often delayed to avoid breaking dependent systems. Deprecated APIs may continue to handle traffic while no longer being documented or actively maintained, placing them outside current governance assumptions.

Internal APIs Becoming Externally Reachable

APIs designed for internal use can become externally reachable due to network configuration changes, cloud exposure, or integration requirements. When exposure assumptions change without corresponding updates to security controls, internal APIs effectively become shadow APIs.

Partner and Third Party Integrations

Integrations with partners and external services introduce APIs that may not be fully visible to internal security teams. Changes in integration logic or vendor behavior can create new access paths without explicit review or documentation.

Automation and AI Driven Systems

Automation frameworks and AI driven systems can generate API calls, orchestrate workflows, or expose dynamic interfaces at runtime. These systems operate at a speed and scale that exceeds traditional governance processes, increasing the likelihood that APIs will exist outside documented controls.

Each of these mechanisms is common in enterprise environments. Together, they ensure that shadow APIs will continue to emerge unless governance and security controls are aligned with how APIs are actually deployed and executed in production.

Security Risks of Shadow APIs

Shadow APIs introduce security risk because they operate outside the controls that organizations rely on to enforce authentication, authorization, monitoring, and policy compliance. These APIs are active in production environments but are often excluded from security reviews, testing pipelines, and incident response planning.

1. Inconsistent Authentication and Authorization

Shadow APIs frequently lack consistent access controls. They may use outdated authentication mechanisms, incomplete authorization checks, or assumptions based on internal trust. Because these APIs are not visible to central security teams, weaknesses can persist without remediation.

When authorization logic is incomplete or misapplied, shadow APIs can allow unauthorized access to data or functionality that would otherwise be protected.

2. Lack of Monitoring and Alerting

Security monitoring and alerting systems are typically configured around known APIs and documented traffic patterns. Shadow APIs may not be included in logging, metrics, or alerting configurations, limiting visibility into how they are used.

As a result, abuse or anomalous behavior can occur without triggering detection mechanisms, increasing dwell time during security incidents.

3. Sensitive Data Exposure

APIs often provide direct access to backend systems and data stores. Shadow APIs may expose sensitive data without appropriate classification, masking, or access restrictions. This includes personal data, financial information, or internal system details.

Because these APIs operate outside expected governance, data handling through shadow APIs may not align with privacy or compliance requirements.

4. Expanded and Unmeasured Attack Surface

Shadow APIs increase the effective attack surface beyond what security teams expect or measure. Attackers actively enumerate APIs using predictable patterns, error responses, and automated scanning techniques.

APIs that are not included in inventories or protected by gateways become attractive targets because they are less likely to be monitored or hardened.

5. Complications in Incident Response and Remediation

During a security incident, shadow APIs complicate investigation and response. Teams may not be aware of all active interfaces involved in an attack, delaying containment and remediation efforts.

The absence of ownership and documentation further slows response, increasing the potential impact of security events.

Shadow APIs do not introduce new threat categories. They amplify existing risks by removing visibility and control. The primary security issue is not the existence of these APIs, but the lack of mechanisms to observe and manage them during execution.

How Shadow APIs Evade Traditional Controls

Shadow APIs evade traditional security controls because those controls are designed around assumed inventories, predefined routes, and documented interfaces. When APIs operate outside these assumptions, enforcement mechanisms fail to apply.

Reliance on Design Time Inventories

Many security programs depend on API inventories created from documentation, specifications, or registration workflows. These inventories reflect intended architecture rather than observed behavior. APIs that are deployed without registration, modified outside formal processes, or generated dynamically are excluded from these records.

As a result, controls that rely on inventories cannot protect APIs that are not known to exist.

Limited Visibility of Gateways and WAFs

API gateways and web application firewalls enforce policies only on traffic that passes through them. Shadow APIs may bypass these controls entirely due to routing decisions, internal service communication, or deployment outside gateway coverage.

Even when gateways are present, they do not observe internal or east–west traffic by default. APIs exposed through internal networks or service meshes may operate without inspection.

Documentation and Specification Drift

OpenAPI specifications and documentation are often used as the basis for security testing and policy enforcement. Over time, code changes diverge from these specifications. Endpoints may be added, modified, or deprecated without corresponding updates to documentation.

When documentation no longer reflects runtime reality, security controls based on those artifacts become incomplete.

Fragmented Ownership and Accountability

Shadow APIs frequently lack clear ownership. When responsibility for an API is unclear, security policies may not be consistently applied or reviewed. Fragmented ownership also complicates remediation when issues are discovered.

Traditional controls assume clear accountability. Shadow APIs undermine this assumption.

Blind Spots in Internal and Automated Traffic

Internal service to service communication and automated workflows generate significant API traffic. This traffic may not be logged or inspected at the same level as external requests. Shadow APIs operating in these paths can remain invisible to perimeter focused security tooling.

Traditional controls are effective within their intended scope. Shadow APIs exist outside that scope because they are not aligned with how controls are deployed and enforced. Addressing this gap requires visibility into APIs as they operate in production rather than reliance on design time assumptions.

Shadow APIs vs Related Concepts

The term “shadow API” is often used interchangeably with several related concepts. While these categories overlap, they describe different conditions and risk profiles. Clear differentiation is necessary to avoid misclassification and incomplete remediation.

Shadow APIs vs Undocumented API Endpoints

Undocumented API endpoints are specific interfaces that exist in production but are not described in official documentation or specifications. Shadow APIs are a broader category. An API can be documented and still be a shadow API if it bypasses monitoring, enforcement, or governance controls.

Undocumented endpoints are therefore a subset of shadow APIs. The defining characteristic of a shadow API is not the absence of documentation, but the absence of effective oversight.

Shadow APIs vs Zombie APIs

Zombie APIs typically refer to deprecated or legacy APIs that are no longer intended for use but remain reachable. These APIs may receive little or no traffic. Shadow APIs, by contrast, are actively handling requests and participating in application workflows.

A zombie API becomes a shadow API when it continues to process traffic without being monitored, secured, or governed. Not all shadow APIs are legacy interfaces, and many are actively developed and used.

Shadow APIs vs Rogue APIs

Rogue APIs imply intentional creation or exposure outside approved processes, often with malicious or unauthorized intent. Shadow APIs do not require intent. They frequently emerge from legitimate development and operational practices.

Classifying all shadow APIs as rogue obscures the underlying issue, which is a gap between delivery velocity and governance capability rather than deliberate misuse.

Shadow APIs vs Shadow IT

Shadow IT refers to technology systems or tools used without organizational approval or visibility. Shadow APIs share a similar visibility problem but operate at a different layer. APIs often serve as foundational infrastructure rather than end user tools.

The impact of shadow APIs is amplified because they directly expose application logic and data. Unlike many forms of shadow IT, shadow APIs can be exploited remotely and at scale.

Distinguishing these concepts helps organizations prioritize controls appropriately. Shadow APIs require detection and governance mechanisms aligned with runtime behavior rather than approaches designed for documentation gaps, legacy cleanup, or policy enforcement alone.

Why Runtime API Discovery Is Required

Shadow APIs cannot be identified reliably through documentation, specifications, or periodic assessments. These mechanisms describe intended architecture and registered interfaces rather than observing how APIs operate in production environments.

Observing APIs as They Operate in Production

Runtime discovery identifies APIs based on observed request and response traffic. APIs are detected according to actual execution paths rather than declared configuration. This includes interfaces introduced through automation, incremental changes, or integration logic that are not reflected in design time artifacts.

Detection is based on behavior rather than registration status.

Detecting Unknown Endpoints and Access Paths

Runtime discovery surfaces endpoints, methods, and parameters that do not appear in existing inventories or specifications. This includes APIs exposed through internal networks, partner integrations, service meshes, or alternate routing paths.

Access paths that bypass documented gateways or registered interfaces are not represented in specification driven tooling or inventory based controls.

Mapping Data Flows in Motion

APIs function as data transfer mechanisms between systems. Runtime discovery observes which APIs handle data, the direction of data movement, and the types of payloads exchanged.

This enables identification of APIs that process sensitive or regulated data regardless of documentation status. Risk assessment is therefore based on observed behavior rather than assumed classification.

Continuous Discovery Rather Than Periodic Assessment

API surfaces change continuously as services are deployed, updated, or reconfigured. Periodic assessments capture a point in time view that does not account for changes occurring between review cycles.

Runtime discovery operates continuously and reflects current execution state rather than historical intent.

Aligning Governance With Execution

Governance decisions depend on an accurate understanding of operational systems. Runtime discovery provides a factual basis for assigning ownership, applying controls, and prioritizing remediation.

Design time models describe how APIs are expected to behave. Runtime discovery describes how APIs actually behave. Shadow APIs persist when governance relies exclusively on the former.

How Levo Addresses Shadow APIs in Production

Levo addresses shadow APIs by observing API behavior at runtime and correlating that behavior with security and governance context. The approach is based on execution visibility rather than reliance on documentation, specifications, or assumed architecture.

Runtime Derived API Inventory

Levo builds an API inventory based on observed production traffic. APIs are identified according to the endpoints, methods, and parameters that actively process requests rather than those declared in specifications or manually registered.

This inventory reflects the current operational API surface, including APIs that bypass gateways, operate internally, or emerge through automation and integration workflows.

API Detection Through Live Traffic

Levo detects APIs by analyzing request and response flows across environments. APIs that are not represented in existing inventories or documentation are identified through observed behavior.

Detection is continuous and reflects changes in execution state as APIs are introduced, modified, or deprecated.

API Monitoring and Behavioral Context

Levo monitors how APIs are used over time, including access patterns, request frequency, and data exchange characteristics. Monitoring is applied to APIs regardless of whether they are documented or formally owned.

This provides context required to assess how APIs operate rather than relying on static classification.

Sensitive Data Discovery in API Traffic

Levo analyzes API traffic to identify the presence and movement of sensitive data. Data handling is observed directly from payloads in motion rather than inferred from documentation or design assumptions.

This enables identification of shadow APIs that process regulated or high risk data without appropriate oversight.

Vulnerability and Risk Correlation

Levo correlates runtime API behavior with indicators of security risk, including inconsistent authentication, excessive data exposure, and anomalous usage patterns.

Risk assessment is based on observed execution characteristics rather than registration status or intended use.

Levo’s approach aligns API security controls with how APIs operate in production. Shadow APIs are addressed by observing and governing execution rather than attempting to enforce completeness at design time.

Conclusion: Why Shadow APIs Require Runtime Visibility

Shadow APIs exist because API execution diverges from documented and governed assumptions. This divergence occurs as systems evolve, ownership fragments, and automation increases.

Design time controls describe intended architecture. They do not provide visibility into how APIs operate once deployed. As a result, APIs that are active in production but absent from inventories remain outside enforcement scope.

Runtime visibility provides a representation of the API surface based on execution rather than intent. This representation is required to identify active APIs, understand how they are used, and apply controls consistently.

Shadow APIs persist when governance relies exclusively on documentation and registration. Runtime visibility provides the basis for aligning security controls with operational reality.