API9:2023 – Improper Inventory Management: Risks and Prevention

APIs are the backbone of modern applications, but they come with their own set of security challenges. One of the most overlooked risks is Improper Inventory Management, now listed as the ninth most critical issue in the OWASP API Security Top 10 (2023).

This blog breaks down what the vulnerability is, why it happens, and how to protect your APIs from this widespread yet preventable threat.

What Is Improper Inventory Management?

Improper Inventory Management refers to the lack of visibility into all active APIs, versions, endpoints, and data flows within your application ecosystem. When organizations fail to maintain an accurate, up-to-date inventory of APIs and their documentation, they create blind spots that attackers can exploit.

These blind spots include:

• Shadow APIs: Unknown or undocumented APIs not tracked by security tools.
• Zombie APIs: Deprecated or forgotten APIs still accessible in production.
• Shadow Parameters: Parameters that exist but are not included in API documentation.
• Incomplete Schemas: APIs with incorrect or missing parameter definitions (e.g., vague data types like String instead of UUID).

Such gaps increase the attack surface and hinder detection, response, and remediation efforts.

Why It Happens: Root Causes

Several operational and architectural factors contribute to improper inventory management:

1. Outdated or Missing Documentation: Manual documentation methods often lag actual deployments.
2. No Central Inventory System: Without a single source of truth, APIs become fragmented across teams and environments.
3. Lack of Retirement Strategy: Old versions remain active and vulnerable without being phased out.
4. Microservices and Cloud Complexity: With increased reliance on distributed systems like Kubernetes and public clouds, API sprawl becomes harder to track.
5. Reliance on Static Security Controls: Tools like WAFs and API gateways rely on predefined schemas, which may not reflect the current state of the APIs.

Real-World Example: The Optus Data Breach

In September 2022, Optus, one of Australia’s largest telecom companies, suffered a major data breach due to an unprotected API. The API exposed 11.2 million customer records, including sensitive PII like names, addresses, and passport numbers.

The root cause? A production API with inadequate access controls and inventory tracking, which went unnoticed until it was too late.

• Impact: Reputational damage, legal scrutiny, and over A$140 million set aside to cover breach-related costs.

Attack Vectors & Threat Landscape

Improper Inventory Management makes it easier for attackers to find and exploit APIs that have been forgotten, poorly documented, or never officially released. These hidden or mismanaged APIs often bypass standard security controls and are left exposed to the public internet.

• Exploitability: Easy – Attackers can discover vulnerable endpoints with minimal effort using automated tools.
• Prevalence: Widespread – Many organizations fail to maintain accurate API inventories, especially during rapid development or version rollouts.
• Detectability: Average – These attacks often go unnoticed until after the damage is done, due to limited monitoring on undocumented endpoints.

Common exploitation techniques include:

• Brute Force on Unsecured Endpoints: Beta or internal APIs often lack rate-limiting or authentication, allowing attackers to guess credentials or tokens repeatedly.
• DNS Enumeration and Google Dorking: Public search tools can reveal forgotten subdomains or APIs left exposed due to misconfigurations.
• Targeting Third-Party Integrations: APIs shared with vendors or partners may leak data if inventory and access controls aren’t regularly reviewed.
• Exploiting Shadow Parameters: Attackers manipulate undocumented parameters to bypass validation logic or access hidden functionality.

Example Scenarios

1. Brute Force via Beta API

Consider a hypothetical scenario where a company launches a beta version of its API to support mobile app testing but doesn’t implement rate-limiting or authentication controls. Attackers discover this endpoint through automated scanning and launch a brute-force attack on the password reset function. Because the API lacks logging and isn’t covered by existing security tools, the attack goes undetected, allowing unauthorized access to multiple user accounts.

2. Data Leak via Misconfigured API

Consider a scenario where a legacy API at a social networking platform remains accessible even after being replaced by a newer version. The outdated API continues to be integrated with several third-party applications, but the organization no longer maintains an up-to-date inventory or visibility into its usage. A malicious application discovers and exploits this oversight to extract user data. Since the API lacks proper monitoring and validation, the activity goes unnoticed, resulting in a silent data leak.

Why Traditional Tools Fail

Traditional tools like API gateways rely on static configurations and imported API schemas, often from outdated or incomplete OpenAPI/Swagger files. When documentation doesn’t match reality, these tools fail to protect what runs in production.

They also lack continuous API discovery. This means shadow APIs (undocumented) and zombie APIs (deprecated but still live) go undetected, leaving critical gaps in security coverage.

Most of these tools don’t validate real-time API behavior or track parameter-level data flows. They cannot identify sensitive data exposure or deviations in how APIs are used unless it has been explicitly defined — which is rarely the case in fast-changing environments.

How to Prevent Improper Inventory Management

Securing your APIs against this vulnerability requires continuous visibility, proactive management, and automation:

1. Establish a Central API Inventory

• Catalog all APIs (internal, public, partner) along with versions, endpoints, and environments.
• Include network access rules and integrated services in your records.

2. Automate Schema and Documentation Generation

• Use tools that automatically generate and update OpenAPI (OAS) documentation.
• Include details on parameters, authentication methods, CORS settings, and error responses.

3. Limit Access to API Documentation

• Restrict access to sensitive documentation to authorized users only.
• Avoid exposing non-production APIs or documentation publicly.

4. Retire Deprecated APIs

• Identify and decommission unused or outdated API versions.
• Perform risk analysis before releasing newer versions and keep the inventory updated.

5. Avoid Using Production Data in Development

• Isolate environments and sanitize data to prevent leakage from testing or staging APIs.

6. Leverage Advanced API Security Tools

• Deploy solutions that offer real-time API discovery, inventory management, and anomaly detection.
• Ensure the tool detects shadow APIs, tracks changes, and alerts discrepancies between schema and actual deployment.

How AppTrana API Protection Helps

Improper Inventory Management often comes down to APIs you didn’t know existed — shadow or outdated endpoints left exposed without proper documentation. AppTrana’s fully managed API security solution helps close these gaps by automatically discovering all internet-facing APIs, including undocumented and deprecated versions. It also provides detailed insights into their behavior, parameters, and data sensitivity.

Unlike traditional tools that rely on static schemas, AppTrana dynamically maps APIs in real time and enriches them with critical metadata such as method type, authentication status, and risk tags (e.g., PII-sensitive or deprecated). This enables security teams to maintain a complete, up-to-date API inventory.

AppTrana also has the option to automate positive security models on newly discovered APIs, enforcing strict, allow-listed access controls from day one.

With built-in risk-based classification, instant policy enforcement on newly discovered APIs, and change tracking to prevent regression vulnerabilities, AppTrana ensures no API slips through the cracks, even in rapidly evolving environments.

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