OWASP API Security Top 10 2023: The Most Critical API Security Risks

APIs are the invisible foundation of the digital world. They connect applications, enable data flows, and create seamless user experiences. However, this central role also makes APIs a preferred target for cybercriminals.

The Open Web Application Security Project (OWASP) regularly publishes the API Security Top 10, a list of the most critical security risks for APIs. The 2023 version makes it clear: API security has become more complex and requires a systematic approach.

Why API Security Matters

Modern applications rely on hundreds or even thousands of API calls. A single insecure endpoint can become a gateway for attackers. The consequences range from data leaks and compliance violations to financial damages in the millions.

According to the State of API Security Report 2023 by Salt Security, API attacks have increased by over 400% in recent years. At the same time, many organizations still do not have their API security under control.

The OWASP API Security Top 10 2023 at a Glance

The ten most critical risks include Broken Object Level Authorization in first place, followed by Broken Authentication and Broken Object Property Level Authorization. Positions four through six are occupied by Unrestricted Resource Consumption, Broken Function Level Authorization, and Unrestricted Access to Sensitive Business Flows. The remaining positions go to Server Side Request Forgery, Security Misconfiguration, Improper Inventory Management, and finally Unsafe Consumption of APIs.

The Top 10 in Detail

API1:2023 – Broken Object Level Authorization (BOLA)

BOLA remains the most critical API security risk. APIs often fail to adequately verify whether a user is actually authorized to access the requested object. A typical example: A user changes the ID in the URL /api/users/123/orders to 124 and suddenly gains access to another user’s orders.

As a countermeasure, an authorization check at the object level should be implemented for every API call. UUIDs instead of sequential IDs make it significantly harder to guess valid references. It is also important to never rely solely on client-side validation.

API2:2023 – Broken Authentication

Weak authentication mechanisms allow attackers to compromise legitimate user accounts or bypass them entirely. Common vulnerabilities include missing rate limiting on login attempts, weak token generation or validation, plaintext transmission of credentials, and missing multi-factor authentication.

Implementing OAuth 2.0 or OpenID Connect combined with strong token mechanisms such as JWT with short expiration times provides a remedy. Rate limiting and account lockout should be standard practice.

API3:2023 – Broken Object Property Level Authorization

This category combines the former risks of Excessive Data Exposure and Mass Assignment. APIs often return more data than necessary or accept input data without proper validation. An example: An API returns internal fields like isAdmin or passwordHash when querying user information.

Response filtering helps here, where only actually needed fields are returned. Input validation with explicit allowlists and schema validation for requests and responses round out the protection.

API4:2023 – Unrestricted Resource Consumption

Without appropriate limits, attackers can overload APIs or cause high costs, especially with cloud-based services. Typical attack vectors include denial of service through mass requests, resource exhaustion during compute-intensive operations, and billing attacks on pay-per-use models.

Rate limiting per user, IP, and API key is essential here. Pagination should be implemented for list endpoints, and timeouts as well as maximum payload sizes need to be defined.

API5:2023 – Broken Function Level Authorization

Attackers can call administrative or privileged functions when authorization at the function level is missing. An example: A regular user can call /api/admin/users/delete because only authentication, not the role, is being verified.

Role-Based Access Control (RBAC) is key here. Administrative endpoints should be isolated in separate API gateways, and the deny-by-default principle should always apply.

API6:2023 – Unrestricted Access to Sensitive Business Flows

This category is new in the 2023 version. Attackers abuse legitimate business processes through automation, such as ticket scalping, credential stuffing, or automated coupon redemption.

Bot detection and CAPTCHA for critical flows can help here. Behavioral analysis and anomaly detection help identify automated attacks. Business logic validation such as purchase limits rounds out the protection.

API7:2023 – Server Side Request Forgery (SSRF)

Also new in 2023: SSRF attacks allow manipulation of the server so that it sends requests to internal systems or external targets.

URL validation with strict allowlists is mandatory here. Network segmentation for backend services makes attacks more difficult, and outgoing connections should be actively monitored and restricted.

API8:2023 – Security Misconfiguration

Faulty configurations are a common entry point. Typical problems include CORS misconfiguration, enabled debug endpoints in production, missing TLS encryption, and default credentials.

Automated security scans in the CI/CD pipeline help detect such problems early. Infrastructure as Code with security baselines and regular configuration audits should be standard.

API9:2023 – Improper Inventory Management

Organizations often lose track of their API landscape. Shadow APIs and outdated endpoints become security risks.

A maintained and automatically updated API inventory provides a solution. An API gateway as a central access point helps with oversight, and deprecation policies for old API versions ensure that outdated interfaces do not become a risk.

API10:2023 – Unsafe Consumption of APIs

Also new in 2023: Using external APIs also carries risks. Blind trust in third-party APIs can lead to security vulnerabilities.

External API responses should always be validated. Timeouts and circuit breakers protect against failures, and third-party APIs should be regularly assessed for security.

Conclusion: API Security as a Continuous Process

The OWASP API Security Top 10 2023 shows that API security is not a one-time project but a continuous process. The new categories like Unrestricted Access to Sensitive Business Flows and SSRF demonstrate that the threat landscape is constantly evolving.

As next steps, it is recommended to create and maintain an API inventory and integrate automated security tests into the CI/CD pipeline. Regular penetration tests and training for developers in API security round out a solid security approach.

Sources and Further Reading

The official OWASP API Security Top 10 2023 documentation can be found at https://owasp.org/API-Security/editions/2023/en/0x11-t10/

The State of API Security Report 2023 by Salt Security is available at https://salt.security/api-security-trends

Further information is provided by the OWASP API Security Project at https://owasp.org/www-project-api-security/ and the NIST Cybersecurity Framework at https://www.nist.gov/cyberframework

Additionally, the CWE/SANS Top 25 Software Weaknesses at https://cwe.mitre.org/top25/ is worth a look.