APIs sit at the center of modern software. Mobile apps, SaaS platforms, and microservices all rely on them to exchange data and trigger actions. In simple terms, APIs are the doors through which systems talk to each other.
That same access makes them a prime target. Each exposed endpoint increases risk. A single weak check can allow attackers to read, modify, or disrupt sensitive data at scale.
Over the past few years, many high-profile breaches have traced back to API issues such as broken authorization, excessive data exposure, or poor rate limiting. These are not edge cases. They are common patterns that repeat across industries.
To standardize how teams approach these risks, the OWASP introduced the API Security Top 10 (2023). It highlights the most critical and recurring API vulnerabilities seen in real world systems. Conducting a thorough API security scan helps teams identify these weaknesses early, which reduces the chance of a breach.
Think of it as a checklist similar to basic hygiene in manufacturing. Skipping one step may not fail immediately, but it increases the chance of a serious issue later.
For engineering, security, and product teams, the framework serves three practical purposes:
Identify where APIs are most likely to fail
Prioritize fixes based on real attack patterns
Build security into development, not after release
In this guide, you will find a clear breakdown of each risk, how attacks typically happen, and what teams can do to prevent them.
What the OWASP API Security Top 10 Is?
The OWASP API Security Top 10 is a curated list of the most critical API vulnerabilities, maintained under the OWASP API Security Project. It highlights real risks observed across modern systems and serves as a practical framework for API security testing.
Its purpose is simple. Improve security awareness and help teams focus on the risks that matter most. Instead of guessing, developers and security teams can follow a proven list of API security risks.
APIs need a dedicated framework because they expose direct access to data and logic. Unlike traditional web apps, APIs often lack user interfaces, which makes issues harder to detect. A single weak endpoint can expose large datasets.
Modern applications rely heavily on application programming interfaces across microservices, mobile apps, and third party integrations. Each connection increases the attack surface.
The framework is designed for developers, architects, AppSec teams, and security leaders who need clear guidance to identify and reduce API threats early.
OWASP API Top 10 vs OWASP Top 10 for Web Applications
The OWASP Top 10 focuses on common web application vulnerabilities like injection, XSS, and misconfigurations. In contrast, the OWASP API Top 10 2023 targets risks specific to API endpoints, such as broken object level authorization and excessive data exposure.
APIs follow different application security models. They expose data directly, often without a user interface. That changes the threat model. Attackers interact with raw endpoints instead of forms or pages. To properly evaluate these risks, security teams follow a structured API pentest method, testing each endpoint for potential flaws before they can be exploited.
OWASP maintains separate projects because the scope and attack patterns differ across these security domains. Still, there is overlap. Issues like authentication flaws and security misconfigurations exist in both.
Together, both frameworks complement each other. One secures the frontend layer, the other protects backend data access. Using both gives broader coverage across modern systems.
How the OWASP API Security Top 10 Is Created?
The OWASP API Top 10 is built through a community-driven process. Security researchers, companies, and practitioners contribute real world data on API vulnerabilities and attack patterns.
OWASP collects inputs from vulnerability reports, bug bounty programs, and incident analysis. Patterns are grouped into clear categories through structured vulnerability classification.
Each risk is evaluated using the OWASP Risk Rating Methodology. It considers factors like vulnerability prevalence, exploitability, and impact. Risks that are both common and easy to exploit rank higher.
The draft list then goes through expert review. Security professionals validate relevance and ensure alignment with current threat models.
The list evolves because the API threat landscape changes. New attack techniques, cloud architectures, and integration patterns introduce fresh risks over time.
What Changed in the OWASP API Top 10? (2019 vs 2023)
The 2023 update reflects how API risks have shifted with cloud-native and microservices architectures. The framework evolved to match a broader and more complex API threat model.
Several categories were refined or merged to reduce overlap. For example, authorization issues were clarified with deeper focus on object and property level access.
New risks were added based on real attack trends. These include BOPLA (Broken Object Property Level Authorization), SSRF (Server Side Request Forgery), and Unrestricted Resource Consumption. Each highlights gaps seen in modern API designs, especially in distributed systems.
The update also improves the overall security taxonomy. It groups risks more clearly, making it easier for teams to map vulnerabilities and prioritize fixes.
API threats have evolved because systems now rely on interconnected services, third party APIs, and automated workflows. More connections mean more entry points, and small weaknesses can scale into major issues.
OWASP API Security Top 10 (2023) at a Glance
A quick view of the API Security Top 10 helps teams understand common API attack patterns and where systems often fail.
Risk | What it means | Typical attack scenario |
API1: Broken Object Level Authorization (BOLA) | Missing checks allow access to other users data | Attacker changes an ID in the request to fetch another user’s records |
API2: Broken Authentication | Weak or flawed login/session handling | Stolen tokens or brute force leads to account takeover |
API3: Broken Object Property Level Authorization (BOPLA) | Overexposed object properties without proper filtering | Hidden fields like isAdmin get modified via API request |
API4: Unrestricted Resource Consumption | No limits on requests or processing | Bot floods API, causing downtime or high cloud costs |
API5: Broken Function Level Authorization | Users access functions beyond their role | Normal user calls admin-only endpoints |
API6: Unrestricted Access to Sensitive Business Flows | Critical flows lack abuse protection | Bot automates purchases or OTP requests at scale |
API7: Server Side Request Forgery (SSRF) | API fetches external resources without validation | Attacker forces server to access internal systems |
API8: Security Misconfiguration | Poor setup exposes unnecessary data or features | Debug endpoints or open storage buckets get exposed |
API9: Improper Inventory Management | Untracked or old APIs remain active | Deprecated endpoints become entry points for attackers |
API10: Unsafe Consumption of APIs | Blind trust in third-party APIs | Compromised external API injects malicious data |
API1: 2023 Broken Object Level Authorization (BOLA)
Broken Object Level Authorization (BOLA) is a critical API vulnerability where an application fails to properly verify whether a user is allowed to access a specific object.
In simple terms, the system checks who you are but not what you should be allowed to access.
It is closely related to IDOR (Insecure Direct Object Reference) and is one of the most common API security flaws in both REST API and GraphQL systems.
How it happens: Attackers modify object identifiers like /users/101 → /users/102, leading to horizontal privilege escalation.
Example: Accessing another user’s /accounts/{id} by changing the ID.
Impact: Exposes sensitive data and allows unauthorized actions.
Prevention: Enforce strict server-side access control, validate ownership, use indirect IDs, and follow least privilege.
API2: 2023 Broken Authentication
Broken Authentication occurs when APIs fail to properly verify user identity, leading to unauthorized access.
How it happens: Weak login systems, poor session management, and misused tokens like JWT enable attacks such as credential stuffing and token hijacking.
Example: Reusing stolen tokens to access accounts without re-authentication.
Impact: Leads to account takeover and full access to user data.
Prevention: Use strong authentication with OAuth 2.0 and OpenID Connect, secure token storage, enable MFA, and enforce proper token validation and expiration.
API3: 2023 Broken Object Property Level Authorization
Weak field level security exposes sensitive fields in a JSON payload or API response. Leads to excessive data exposure and mass assignment attacks.
Example: Hidden fields like isAdmin=true get modified.
Prevention: Filter responses, validate input, apply data minimization, secure serialization.
API4: 2023 Unrestricted Resource Consumption
No rate limits allow resource exhaustion and denial of service. Attackers overload APIs with repeated requests.
Impact: Downtime and cost spikes.
Prevention: Use throttling, quotas, and controls via API Gateway.
API5: 2023 Broken Function Level Authorization
APIs fail to restrict access to sensitive functions, causing vertical privilege escalation.
Example: Normal user accessing admin endpoints.
Prevention: Enforce server-side checks using RBAC and ABAC.
API6: 2023 Unrestricted Access to Sensitive Business Flows
Attackers abuse logic in flows like checkout API or signup API.
Example: Coupon abuse via automation.
Prevention: Detect anomalies, limit actions, block bot traffic.
API7: 2023 Server-Side Request Forgery (SSRF)
APIs fetch external URLs without validation, enabling internal access.
Example: Accessing AWS metadata service via user input.
Prevention: Validate URLs, restrict outbound requests, secure webhooks.
API8: 2023 Security Misconfiguration
Weak defaults, open CORS, or exposed tools like Swagger UI create risks. Mismanaged systems like Kubernetes increase exposure.
Prevention: Harden configs, disable debug endpoints, enforce secure deployment.
API9: 2023 Improper Inventory Management
Untracked or outdated APIs increase attack surface. Shadow and deprecated endpoints go unnoticed.
Prevention: Maintain inventory using OpenAPI and manage through API Gateway.
API10: 2023 Unsafe Consumption of APIs
Trusting a third-party API without validation introduces supply chain risks.
Example: Malicious or compromised SaaS integration.
Prevention: Validate data, enforce trust boundaries, and audit dependencies.
How to Test APIs for OWASP Top 10 Vulnerabilities?
Testing APIs for security weaknesses is critical to prevent breaches and ensure compliance. A structured approach combines manual testing, automated scans and penetration methods to cover all possible risks.
1. Manual API Testing Techniques
Manual testing is critical for understanding the logic behind APIs. Start by exploring endpoints with tools like Postman. Test for:
Broken Object Level Authorization (BOLA): Modify object identifiers (/users/101 → /users/102) to check if unauthorized data is accessible.
Broken Authentication: Attempt login bypasses, token reuse, or session manipulation.
Excessive Data Exposure: Inspect API responses for fields that should not be returned.
Example: Sending a PATCH request to /api/accounts/2001 while logged in as another user can reveal mass assignment flaws.
2. Automated Security Scanning
Dynamic testing tools detect vulnerabilities at scale:
DAST (Dynamic Application Security Testing) tools like Burp Suite or OWASP ZAP can automatically scan for common API flaws such as SQL injection, IDOR, or misconfigured CORS.
SAST (Static Application Security Testing) can analyze code in CI/CD pipelines to detect insecure patterns like hardcoded tokens or missing authorization checks.
3. API Penetration Testing
Simulate real attacks to validate API security:
Credential stuffing to check for weak authentication.
Token hijacking tests if JWT or OAuth tokens can be misused.
Mass assignment and object manipulation for BOLA and property-level authorization flaws.
4. CI/CD Security Testing
Integrate security into pipelines to catch vulnerabilities early:
Automate SAST/DAST scans for every deployment.
Run regression security tests for new endpoints.
Combine with monitoring for abnormal API behaviors.
API Security Best Practices to Prevent OWASP Top 10 Risks
1. Strong Authentication and Authorization
Use OAuth 2.0 or OpenID Connect for token based access.
Enforce multi factor authentication (MFA) and proper session management.
Implement object level and function level authorization (RBAC/ABAC).
Validate every request on the server side, never rely on client-side checks.
2. Rate Limiting and Resource Protection
Prevent abuse with throttling, quotas, and request limits via API Gateway.
Protect against unrestricted resource consumption and denial of service attacks.
Consider WAF rules for common API attack patterns.
3. Secure API Design
Follow defense in depth: combine authentication, authorization, input validation, and data minimization.
Avoid exposing unnecessary fields in responses.
Sanitize inputs to prevent injection attacks and mass assignment vulnerabilities.
Version APIs carefully to prevent exposure of deprecated endpoints.
4. Continuous Monitoring and Governance
Use SIEM tools for logging, alerting, and anomaly detection.
Track API usage, monitor rate limits, and detect unusual patterns such as sequential object access.
Maintain an up to date API inventory to prevent shadow APIs and misconfigurations.
Integrate DevSecOps practices to ensure security is part of development workflows.
