Understanding OWASP API Security Top 10 (2023 Edition)
A practical guide to the OWASP API Security Top 10 2023. Learn what each vulnerability means, how attackers exploit them, and how to protect your APIs.
APIs now handle more sensitive operations than traditional web applications. Payment processing, authentication, data access. All flow through APIs. Yet many teams apply web security thinking to API problems, leaving critical gaps.
The OWASP API Security Top 10 (2023) addresses this disconnect. It’s not just a list. It’s a framework for understanding how attackers think about your APIs.
API1:2023 Broken Object Level Authorization (BOLA)
The most prevalent API vulnerability. Attackers modify object IDs in requests to access resources belonging to other users. A request to /api/users/123/orders becomes /api/users/124/orders.
Why it’s dangerous: Authorization checks happen at the function level but not the object level. The API confirms you can view orders, but not whose orders you’re viewing.
API2:2023 Broken Authentication
Weak authentication mechanisms let attackers impersonate legitimate users. This includes credential stuffing, brute force attacks, JWT misconfigurations, and session token weaknesses.
Key indicators: Missing rate limits on login endpoints, predictable tokens, credentials in URLs, weak password policies.
API3:2023 Broken Object Property Level Authorization
APIs often expose more data properties than necessary. An endpoint returning user profiles might include internal flags, creation timestamps, or role assignments that clients shouldn’t see or modify.
Attack pattern: Inspecting API responses for extra fields, then attempting to set those fields in update requests (mass assignment).
API4:2023 Unrestricted Resource Consumption
APIs without proper rate limiting or resource constraints are vulnerable to denial-of-service attacks. Attackers flood endpoints, exhaust server resources, or abuse expensive operations.
Common vectors: Pagination abuse (requesting page size of 10,000), complex GraphQL queries, file upload endpoints without size limits.
API5:2023 Broken Function Level Authorization (BFLA)
While BOLA is about accessing the wrong data, BFLA is about accessing the wrong functions. Regular users calling admin endpoints, or customers accessing internal APIs.
Example: Changing GET /api/users/me to DELETE /api/users/me or discovering /api/admin/users exists.
API6:2023 Unrestricted Access to Sensitive Business Flows
Some business operations shouldn’t be automated or executed at scale: purchasing limited items, creating accounts, submitting reviews. Attackers exploit these flows for profit.
Impact: Inventory scalping, fake review generation, coupon abuse, referral fraud.
API7:2023 Server-Side Request Forgery (SSRF)
When APIs fetch remote resources based on user input, attackers can redirect those requests to internal services. A webhook URL field becomes an internal network scanner.
Why APIs are vulnerable: Modern APIs frequently integrate with external services, process URLs from user content, and fetch resources dynamically.
API8:2023 Security Misconfiguration
The catch-all category for deployment mistakes: verbose error messages, missing security headers, unnecessary HTTP methods enabled, default credentials, exposed debug endpoints.
Common findings: Stack traces in error responses, /api/debug endpoints in production, CORS allowing all origins.
API9:2023 Improper Inventory Management
Organizations lose track of their APIs. Old versions stay deployed, internal APIs get exposed, documentation drifts from reality. Attackers find and exploit these forgotten endpoints.
Shadow API risk: Development APIs deployed to production, beta endpoints never decommissioned, undocumented admin APIs.
API10:2023 Unsafe Consumption of APIs
Your API isn’t just a provider. It’s a consumer. When integrating third-party APIs, teams often apply less scrutiny: trusting responses, skipping validation, following redirects blindly.
Attack vector: Compromising a third-party API your service trusts, then using that trust to attack your infrastructure.
Mapping Theory to Detection
Understanding these risks is step one. Detection requires continuous visibility into API traffic patterns, request anomalies, and authorization failures.
Most organizations lack this visibility. Traditional WAFs see HTTP requests but miss API context. SIEM systems have the data but not the API-specific detection logic.
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