Improper Assets Management is an API security vulnerability that arises when an organization lacks a complete, accurate, and up-to-date inventory of its APIs and their endpoints, leaving old, undocumented, or unmanaged APIs exposed and unprotected. It featured in the OWASP API Security Top 10 (as API9:2019) and reflects a governance failure: you cannot secure what you do not know you have. When APIs proliferate without proper tracking, versioning, and retirement, the result is unknown gaps in the attack surface that attackers can exploit.
The vulnerability commonly manifests in a few ways. Old or deprecated API versions are left running in production after being superseded, but they retain vulnerabilities that were fixed in newer versions – attackers seek these out precisely because they are less protected. These are sometimes called “zombie APIs.” Shadow APIs are endpoints that exist but are undocumented and unknown to the security team, so they receive no review, monitoring, or protection. Test, staging, or debug endpoints may be inadvertently exposed. And missing documentation means that even known APIs are not properly understood, including what data they handle and how they should be secured.
The danger of improper assets management is that these unmanaged and forgotten APIs provide attackers with entry points that bypass security controls applied only to known, current APIs. An old version of an endpoint with a known flaw, still reachable in production, is an open door. Because the organization is unaware of these assets, it cannot patch, monitor, or defend them – the attacker effectively has better knowledge of the attack surface than the defender.
This risk is closely tied to API sprawl and to the importance of API discovery. Preventing improper assets management requires maintaining a continuous, comprehensive inventory of all APIs and endpoints – including versions, hosts, and environments – through ongoing discovery; documenting each API’s purpose, data, and security requirements; enforcing versioning and formal retirement processes so deprecated APIs are actually decommissioned rather than left running; and applying consistent security controls across the entire inventory. Governance and visibility are the core remedies: knowing exactly what APIs exist, what they do, and ensuring none are left exposed and forgotten.