What is API Security?
API security refers to the strategies and practices used to protect application programming interfaces (APIs) from attacks, misuse, and vulnerabilities. APIs are the primary interface for connecting services, exchanging data, and enabling integrations between different systems, especially in cloud-native and microservices architectures. API security best practices involve a multi-layered approach to protect APIs from various threats. Key practices include:
- Discover and govern all APIs: Maintain clear and updated API documentation, including security considerations and versioning information, to enable secure development and usage.
- Validate inputs and enforce schemas: Validate and sanitize all input from API clients to prevent common vulnerabilities like SQL injection, cross-site scripting (XSS), and other injection attacks.
- Adopt secure API design standards early: Apply security best practices during API design, such as using secure defaults, input validation, and proper error handling to reduce risk before deployment.
- Use versioning to avoid breaking or exposing data: Version APIs to control access to changes, prevent data leaks, and maintain compatibility across evolving client applications.
- Enforce strong authentication and authorization: Implement robust authentication mechanisms such as OAuth 2.0, OpenID Connect, or API keys. Enforce granular authorization using principles like least privilege and Role-Based Access Control (RBAC) to ensure users and applications only access necessary resources.
- Protect secrets and tokens: Store secrets like API keys and tokens securely using encrypted vaults, and never embed them directly in source code or configuration files.
- Adopt zero trust principles: Adopt a Zero Trust approach, which assumes no implicit trust and requires verification for every request, regardless of its origin.
- Rotate and manage keys and tokens securely: Automate the rotation of credentials with short lifespans and monitor usage to detect misuse or compromise.
- Use fine-grained scopes and delegated access: Assign limited scopes to tokens and use delegated access to control what data or actions are permitted for third-party integrations.
- Use API gateways for policy enforcement and observability: Utilize API gateways as a central point for enforcing security policies, managing access control, and routing requests, providing a crucial layer of defense for backend services.
- Implement rate limiting and load testing: Implement rate limiting to control the number of requests an API client can make within a specified timeframe, mitigating brute-force attacks and Denial-of-Service (DoS) attacks.
- Encrypt data in transit and at rest: Encrypt all data in transit using secure protocols like TLS 1.2 or higher, and encrypt sensitive data at rest to prevent unauthorized access and interception.
- Implement API protection services: Use specialized tools to detect and mitigate API-specific attacks like abuse, scraping, or injection, supplementing native security features.
- Monitor runtime behavior and anomalies: Maintain detailed logs of API activities and implement continuous monitoring to detect suspicious behavior, unauthorized access attempts, and potential security incidents in real-time.
- Shift security left in the CI/CD: Integrate security tests early in the development pipeline to catch vulnerabilities before deployment and reduce remediation costs.
- Perform regular penetration testing and threat modeling: Conduct frequent security audits, penetration testing, and vulnerability assessments to identify and address weaknesses in API security posture.
- Decommission old APIs promptly and safely: Retire deprecated APIs quickly and securely to prevent them from becoming attack surfaces or compliance risks.
As APIs expose application logic and data to third parties, any security gap can lead to unauthorized access, data exfiltration, or service disruption. The rapid growth of APIs in digital business makes them a frequent target for attackers seeking access to sensitive systems and data.
In this article:
1. Discover and Govern All APIs
Unmanaged, undocumented, or "shadow APIs" often escape security review and governance, leaving organizations exposed to serious risks. Discovery processes use automated tools to scan networks, traffic, and codebases to locate all APIs, including those that have been forgotten or bypassed the official release process. Once APIs are discovered, organizations can catalog them, document their endpoints, and bring them into governance frameworks.
Governance over APIs involves enforcing consistent security policies, tracking changes throughout the API lifecycle, and ensuring compliance with standards. This includes version control, access restrictions, and mandatory authentication. Without robust discovery and governance, even a single unsecured API can provide attackers a reliable beachhead for lateral movement or data extraction.
Learn more in our detailed guide to API discovery.
2. Validate Inputs and Enforce Schemas
Proper input validation ensures that incoming data to APIs meets expected formats, types, and lengths, significantly reducing the risk of injections and data corruption. All client-supplied values, whether in headers, body, or query strings, must pass through stringent validation logic before being processed or stored. Server-side validation is crucial because client-side checks can be manipulated or bypassed by attackers.
Enforcing strict API schema definitions, such as using OpenAPI Specification or JSON Schema, helps reduce ambiguity in what input is acceptable. Automated schema validation tools can reject malicious or malformed input at the earliest point of entry. This not only improves security but also boosts API reliability by preventing errors and unexpected behavior due to bad data.
3. Adopt Secure API Design Standards Early
Adopting secure design principles from the beginning helps prevent vulnerabilities from becoming embedded in APIs. This includes enforcing least privilege, using secure defaults, and designing APIs to fail securely. For example, sensitive operations should require re-authentication or explicit user consent, and error messages should avoid exposing internal details that could aid an attacker.
Design standards also involve defining consistent response formats, status codes, and authentication flows. Using established design patterns such as REST or GraphQL securely, and adhering to specifications like OpenAPI, ensures that APIs are predictable and easier to secure. Early adoption reduces the cost of retrofitting security measures after deployment.
4. Use Versioning to Avoid Breaking or Exposing Data
Versioning allows developers to introduce changes or enhancements without disrupting existing users or exposing unintended data. By maintaining separate versions (e.g., v1, v2) through URL paths or headers, you ensure backward compatibility while phasing out older interfaces in a controlled manner. This reduces the risk of breaking client applications that depend on earlier API behaviors.
From a security standpoint, versioning helps track and manage access to deprecated or less secure API versions. It also enables teams to apply different security policies or controls per version. Deprecated versions should be scheduled for deprecation and removal, with clear communication to users and proper monitoring to enforce transitions.
5. Enforce Strong Authentication and Authorization
Strong authentication means requiring secure credentials for every API request, while strong authorization ensures users and systems only access allowed resources. Popular approaches include OAuth 2.0, OpenID Connect, and mutual TLS, which provide token-based, role-based, or certificate-based mechanisms that make unauthorized access more difficult. It is critical that authentication tokens themselves are not guessable, easily stolen, or improperly validated.
Authorization should operate on the principle of least privilege, granting users or applications only the permissions they need for their intended purpose. Regularly review and update access rules to prevent privilege creep and always separate authentication (verifying identity) from authorization (validating allowed actions). This dual-layered approach significantly reduces the likelihood of both external and insider threats gaining improper access to sensitive functions and data.
6. Protect Secrets and Tokens
APIs rely on secrets such as API keys, tokens, and credentials for access control, authentication, and integration with other services. Exposing these secrets through insecure storage, code repositories, or logs is a common cause of breaches. Organizations should use dedicated secret management tools and secure vaults for storing and managing secrets, ensuring they are encrypted both at rest and in transit.
Developers should avoid embedding secrets in source code, configuration files, or environment variables that are part of version control systems. Additionally, tokens and keys should have proper scopes and expiry periods, and should be rotated frequently. Monitoring for exposed secrets in public and private repositories with automated tools is also key to reducing the window of exposure should a leak occur.
7. Adopt Zero Trust Principles
Zero trust frameworks operate under the assumption that no user or system, internal or external, should be trusted by default. Every API request must be authenticated, authorized, and encrypted, regardless of source or destination. Implementing micro-segmentation, identity-based controls, and continuous verification aligns with zero trust principles for APIs.
Zero trust also means limiting lateral movement in case of a breach, by ensuring APIs only have access to specifically needed resources. This minimizes the potential impact of credential or token theft. Adopting zero trust practices for APIs forces organizations to challenge every access attempt and helps address sophisticated threats not caught by perimeter-based defenses.
8. Rotate and Manage Keys and Tokens Securely
Regular rotation of API keys, tokens, and credentials is crucial in reducing the risk posed by exposed or stolen secrets. Automation can help manage rotation schedules, deprecate unused credentials, and alert teams to potential misuse or compromise. Setting short lifetimes on secrets reduces their value to attackers and limits the exposure window.
Secret management platforms provide secure storage, role-based access controls, and audit trails for all secrets. Integrating these platforms into the CI/CD and deployment workflows streamlines secure key management. Documentation and adherence to secret rotation policies ensure consistency and minimize operational overhead.
9. Use Fine-Grained Scopes and Delegated Access
Fine-grained scopes define the exact actions a token holder can perform, reducing the risk of privilege escalation. Instead of granting full access, scopes limit tokens to specific operations or data, for example, allowing read-only access to profile information but not write access. This makes it harder for a compromised token to be misused beyond its intended function.
Delegated access allows one system or user to act on behalf of another, securely. Standards like OAuth 2.0 support delegated access via authorization grants, enabling scenarios like third-party integrations without exposing user credentials. Always define and enforce scopes clearly, audit their use, and avoid granting overly broad permissions.
10. Use API Gateways for Policy Enforcement and Observability
An API gateway provides a central point to enforce security policies, manage access controls, and monitor API traffic. By placing a gateway in front of backend API services, organizations can implement authentication, rate limiting, and request inspection without modifying application code. Gateways can also enforce protocol transformations, secure headers, and payload encryption for compliance or integration needs.
In terms of observability, modern API gateways provide logging, analytics, and real-time monitoring features. This allows organizations to track usage, identify suspicious patterns, and debug performance issues quickly. Centralization of policy enforcement and observability via gateways simplifies security management, auditability, and incident response.
11. Implement Rate Limiting and Load Testing
Rate limiting constrains the number of requests a client can make within a given timeframe, protecting backend services from abuse, denial-of-service (DoS) attacks, and resource exhaustion. Effective rate limiting mechanisms block or throttle clients who exceed allocated thresholds, ensuring fair use and availability for legitimate users. These mechanisms can be tuned based on endpoint sensitivity, user roles, or other business requirements.
Load testing simulates high-traffic scenarios to identify performance bottlenecks and validate the effectiveness of rate limiting and throttling strategies. Regular load testing helps pinpoint weaknesses in API infrastructure, optimize resource allocation, and ensure the system can handle production-scale workloads without degradation or outages. Combining both practices guards APIs against both intentional attacks and unexpected traffic spikes.
12. Encrypt Data in Transit and at Rest
Data in transit should be protected using TLS 1.2 or higher to prevent interception or tampering. All endpoints, whether public or internal, should enforce HTTPS and reject plaintext HTTP traffic. In addition, use mutual TLS where both client and server identities need to be verified, such as in internal service-to-service APIs.
Encrypting data at rest involves securing stored data using strong encryption algorithms (e.g., AES-256). This protects data in case of storage compromise or unauthorized access. Keys used for encryption must be stored in secure key management systems, with access restricted and audited. Encrypt both primary data and metadata, including logs that might contain sensitive information.
13. Implement API Protection Services
API protection services act as a first line of defense, providing tools and features to detect, block, and mitigate API-specific threats. These services can identify and stop attacks such as API abuse, credential stuffing, injection attacks, and data scraping in real time. By leveraging techniques like traffic analysis, machine learning, and automated threat intelligence, protection services reduce the risk posed by attackers targeting APIs.
Default security mechanisms provided by cloud platforms and API management solutions may not be enough to counter new or targeted attacks. Specialized API protection services can fill these gaps. Investing in these solutions ensures rapid threat detection and response and helps organizations keep pace with evolving attack vectors. These services also typically include dashboards, alerting, and integrations to support incident response workflows.
14. Monitor Runtime Behavior and Anomalies
Continuous monitoring of API traffic in real-time is essential to detect anomalies, such as unusual usage patterns, spikes in failed logins, or out-of-band data access. Logging all API interactions and maintaining detailed audit trails help identify incidents quickly and support forensic investigations after a breach. These logs should capture key attributes, including timestamps, request origins, endpoints accessed, and error codes.
Advanced monitoring uses machine learning or rule-based systems to detect deviations from approved behaviors or previously established baselines. Instance anomalies might indicate compromised credentials, automated bots, or active exploitation attempts. Quick detection and response to unusual activities can prevent minor incidents from escalating into major security breaches or service outages.
15. Shift Security Left in CI/CD
Integrating security checks early in the software development lifecycle (the “shift left” approach) enables teams to catch vulnerabilities before APIs are deployed to production. Automated security testing, static analysis, and dependency scanning during code commits or build processes help uncover issues such as insecure coding practices, vulnerable libraries, or unprotected secrets.
Embedding security controls in CI/CD pipelines not only accelerates remediation but fosters a security-first mindset among developers. This leads to fewer vulnerabilities, reduced technical debt, and continuous compliance with internal or regulatory standards. Regular code reviews, security testing, and automated policy enforcement ensure vulnerabilities are addressed promptly, strengthening API security posture.
16. Perform Regular Penetration Testing and Threat Modeling
Penetration testing simulates real-world attacks on APIs to uncover vulnerabilities that automated tools may miss. These tests should cover authentication, input validation, business logic, and access controls. Third-party testers offer an outside perspective and often identify overlooked risks. Schedule tests regularly and after major API updates.
Threat modeling involves identifying potential threats and attack vectors during the design phase. Use frameworks like STRIDE or DREAD to assess the likelihood and impact of each threat. This helps prioritize defenses and guide secure architecture decisions. Conducting these exercises early and often ensures security is baked into API development rather than bolted on later.
17. Decommission Old APIs Promptly and Safely
Old APIs that remain active after deprecation can become security liabilities, especially if they lack modern protections or are no longer maintained. Define clear deprecation policies and timelines, communicate them to users, and monitor usage to plan phased retirement. Ensure all dependencies are migrated to newer versions before decommissioning.
Decommissioning should include revoking access credentials, removing DNS entries, updating documentation, and verifying logs no longer show active usage. Where feasible, implement redirects or stub endpoints that explain the API is no longer supported. Clean removal helps avoid confusion, reduces attack surface, and prevents legacy code from becoming a hidden vulnerability.
As APIs increasingly expose application logic and sensitive data, securing them requires continuous visibility, strict enforcement, and the ability to detect abuse that traditional controls may miss. Radware API Protection is designed to address these challenges by securing APIs across discovery, governance, and runtime protection.
Radware API Protection helps organizations discover and inventory all APIs, including undocumented and shadow APIs, across cloud-native and hybrid environments. This reduces blind spots that frequently lead to misconfigurations, unauthorized access, and data exposure. By maintaining clear visibility into API surfaces, security teams can apply consistent governance and security policies.
At runtime, the solution enforces schema validation and positive security models, ensuring API requests conform to expected specifications. This limits injection attacks, malformed requests, and logic abuse, even when attackers use syntactically valid inputs. Behavioral analysis further detects anomalous usage patterns such as excessive enumeration, credential abuse, or abnormal request rates that indicate malicious activity over time.
Radware API Protection integrates with other Radware solutions to support a layered API security approach. Cloud WAF complements API protection by enforcing input validation and blocking web-based attacks against API endpoints, while Bot Manager mitigates automated abuse such as scraping, brute-force attempts, and credential stuffing. Threat Intelligence Subscriptions enrich API defenses with real-world attacker context, enabling proactive blocking of known malicious sources. For resilience and availability, DefensePro and Cloud DDoS Protection Service help ensure APIs remain accessible during volumetric and multi-vector attacks.
Together, these capabilities enable organizations to implement API security best practices in practice by combining discovery, governance, runtime enforcement, and continuous monitoring into a unified protection strategy.