Shadow APIs and Zombie APIs: How to Discover and Deprecate Your Invisible Attack Surface

The API Inventory Gap: An Existential Threat 👻

One of the most insidious security problems is the existence of APIs that the security and governance teams don't know about. These hidden endpoints, known as **Shadow APIs** and **Zombie APIs**, form an invisible attack surface that bypasses all security review, monitoring, and policy enforcement, making them easy targets for attackers.

Shadow APIs (The Accidental Attack Surface)

These are endpoints that developers create for testing, debugging, or internal use but forget to secure, document, or remove before deployment. Because they are not in the official API catalog, they often run with weak or default security settings, providing a direct, unmonitored backdoor into the system.

Zombie APIs (The Undead Threat)

These are API versions (e.g., /v1/users) that have been officially deprecated and superseded (e.g., by /v2/users), but the underlying code/service was never fully decommissioned. They remain a threat because they are often running older, vulnerable code, lack modern security patches, and may still expose data via deprecated fields that were filtered in the new version (Excessive Data Exposure risk).

Mitigation Strategy: Discovery and Centralized Control

The solution is a proactive approach focused on continuous discovery and centralized control.

1. Mandate Centralized Traffic through the API Gateway

The single most important step is configuring your network to ensure **all** external API traffic must pass through the **API Gateway**. This makes the gateway the **single source of truth** for all active endpoints, regardless of their documentation status.

2. Continuous Discovery and Auditing

Use the Gateway's comprehensive logging and tracing capabilities to identify all endpoints that receive traffic. Security teams should regularly audit these logs, cross-referencing them against the official **OpenAPI (Swagger) specification**. Any endpoint receiving legitimate traffic that is not in the specification is a potential **Shadow API** that requires immediate documentation or decommissioning.

3. Strict Decommissioning Policies

For **Zombie APIs**, a strict deprecation lifecycle is needed. When an API version is retired, the associated gateway routes must be deleted, and the underlying service (or the specific endpoint code) must be physically removed from the production environment, not just marked as "deprecated."