OpenAPI Specification Extended Security Scheme: A method to reduce the prevalence of Broken Object Level Authorization

Abstract: APIs have become the prominent technology of choice for achieving inter-service communications. The growth of API deployments has driven the urgency in addressing its lack of security standards. API Security is a topic for concern given the absence of standardized authorization in the OpenAPI standard, improper authorization opens the possibility for known and unknown vulnerabilities, which in the past years have been exploited by malicious actors resulting in data loss. This paper examines the number one vulnerability in API Security: Broken Object Level Authorization(BOLA), and proposes methods and tools to reduce the prevalence of this vulnerability. BOLA affects various API frameworks, our scope is fixated on the OpenAPI Specification(OAS). The OAS is a standard for describing and implementing APIs; popular OAS Implementations are FastAPI, Connexion (Flask), and many more. These implementations carry the pros and cons that are associated with the OASs knowledge of API properties. The Open API Specifications security properties do not address object authorization and provide no standardized approach to define such object properties. This leaves object-level security at the mercy of developers, which presents an increased risk of unintentionally creating attack vectors. Our aim is to tackle this void by introducing 1) the OAS ESS (OpenAPI Specification Extended Security Scheme) which includes declarative security controls for objects in OAS (design-based approach), and 2) an authorization module that can be imported to API services (Flask/FastAPI) to enforce authorization checks at the object level (development-based approach). When building an API service, a developer can start with the API design (specification) or its code. In both cases, a set of mechanisms are introduced to help developers mitigate and reduce the prevalence of BOLA.