APIs are the backbone of modern applications. They connect frontends with backends, enable microservice architectures, and power mobile apps. But this central role makes them a prime attack target. OWASP (Open Worldwide Application Security Project) published an updated list of the ten most critical API security risks in 2023.
Why API Security Matters
Over 80% of internet traffic today runs through APIs. At the same time, attacks on API endpoints are growing exponentially. Traditional security measures like Web Application Firewalls (WAFs) fail to detect many API-specific attacks, as these often exploit logical vulnerabilities rather than technical ones.
The OWASP API Security Top 10 2023 Overview
The following list describes the ten most critical security risks for APIs, ordered by severity and frequency.
API1:2023 - Broken Object Level Authorization (BOLA)
Description
BOLA occurs when an API fails to adequately verify whether a user is authorized to access a specific object. Attackers can manipulate IDs in API requests to access other users' data.
Example
An attacker changes /api/users/123/orders to /api/users/456/orders and gains access to another user's orders because the API doesn't verify object ownership.
Countermeasures
- Implement object-level authorization checks on every API request
- Use unpredictable object IDs (e.g., UUIDs instead of sequential IDs)
- Automated testing with different user contexts
API2:2023 - Broken Authentication
Description
Authentication vulnerabilities allow attackers to assume the identity of other users. This includes weak token generation, missing token validation, and insecure password recovery flows.
Example
An API accepts expired JWT tokens or doesn't correctly validate the signature, enabling token forgery.
Countermeasures
- Strict token validation with expiration times and signature verification
- Multi-factor authentication for sensitive operations
- Rate limiting for authentication endpoints
API3:2023 - Broken Object Property Level Authorization
Description
This vulnerability occurs when an API doesn't adequately restrict access to specific object properties. Attackers can read or write sensitive fields that should not be accessible to them.
Example
A user sends an update with {"role": "admin"} in the request body, and the API accepts the role change because it doesn't filter input fields.
Countermeasures
- Whitelist allowed fields for each operation
- Separate read and write models (DTOs)
- Remove sensitive fields from API responses
API4:2023 - Unrestricted Resource Consumption
Description
APIs that don't set limits on resource consumption are vulnerable to denial-of-service attacks. This includes missing rate limits, no payload size restrictions, and unlimited query complexity.
Example
An attacker sends a GraphQL query with deeply nested relationships that overloads the server and makes it unreachable for other users.
Countermeasures
- Implement rate limiting and throttling
- Limit maximum payload size
- Query complexity limits for GraphQL APIs
API5:2023 - Broken Function Level Authorization
Description
When administrative endpoints or sensitive functions are not adequately protected, regular users can perform privileged actions.
Example
A regular user changes GET /api/users to DELETE /api/users/123 and can delete user accounts because function-level authorization isn't checked.
Countermeasures
- Role-based access control (RBAC) for all endpoints
- Isolate administrative functions in separate API segments
- Deny all access by default (Deny by Default)
API6:2023 - Unrestricted Access to Sensitive Business Flows
Description
APIs that expose business-critical flows without restricting their automated usage are vulnerable to abuse by bots and automated attacks.
Example
An attacker automates the purchase process of a limited product and buys the entire stock before regular customers have a chance.
Countermeasures
- Bot detection and CAPTCHA for critical business flows
- Device fingerprinting and behavioral analysis
- Business logic-based rate limits
API7:2023 - Server Side Request Forgery (SSRF)
Description
SSRF occurs when an API fetches user-supplied URLs without adequate validation. Attackers can use the API to reach internal services.
Example
An API accepts a URL parameter to download an image. An attacker passes http://169.254.169.254/latest/meta-data/ and receives AWS metadata including credentials.
Countermeasures
- Strict URL validation and whitelisting of allowed domains
- Block requests to internal networks and cloud metadata endpoints
- Use a proxy server for outgoing requests
API8:2023 - Security Misconfiguration
Description
Misconfigurations at any level of the API stack can open security gaps. This includes unnecessarily open ports, missing security headers, enabled debug mode, and default credentials.
Example
An API allows CORS requests from any origin (Access-Control-Allow-Origin: *), thereby exposing sensitive data to arbitrary websites.
Countermeasures
- Automated configuration audits and hardening
- Restrictive CORS policies and security headers
- Disable debug modes and unnecessary features in production
API9:2023 - Improper Inventory Management
Description
Organizations lose track of their API landscape. Outdated API versions, undocumented endpoints, and forgotten test environments provide attackers with entry points.
Example
An old API version (/api/v1/) remains active after the upgrade to v2 and contains vulnerabilities that have long been fixed in the new version.
Countermeasures
- Complete API inventory and documentation
- Automatic detection of shadow APIs and undocumented endpoints
- Lifecycle management with clear deprecation policies
API10:2023 - Unsafe Consumption of APIs
Description
Developers often trust data from third-party APIs without adequate validation. If a third party is compromised, malicious data can enter your own system.
Example
An application integrates an external weather API and renders its response directly in the frontend. An attacker compromises the weather API and injects malicious JavaScript.
Countermeasures
- Validate and sanitize all data from third-party APIs
- Timeout and error handling for external API calls
- Strict input validation regardless of data source
Conclusion
The OWASP API Security Top 10 2023 clearly shows: API security requires a holistic approach. Traditional security tools are not sufficient to detect the logical and context-aware vulnerabilities that threaten modern APIs.
Automated, agent-based API security platforms like Venedy can close this gap by continuously and context-aware testing APIs against all OWASP Top 10 vulnerabilities.
Sources
- OWASP API Security Project: API Security Top 10 2023
- OWASP Foundation: API Security Risks Overview
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