API security is the practice of safeguarding the interfaces that permit applications to communicate with each other from threats, vulnerabilities, and unauthorized access. This involves implementing protection mechanisms to prevent malicious attacks, enforce data integrity, and ensure the secure exchange of information.
What is API security?
API security encompasses the measures required to protect application programming interfaces (APIs) from potential threats and unauthorized access. It addresses the following core areas:
Threat prevention: Protects APIs from common attacks, including injection, data exposure, and service disruptions through input validation, access controls, and anomaly detection.
Access control: Ensures only authenticated and authorized users and systems can access APIs, using mechanisms such as OAuth 2.0, OpenID Connect, and API keys.
Data protection: Implements encryption for data in transit and at rest, using standards such as TLS 1.3 and field-level encryption.
Business continuity: Prevents disruptions to API services by implementing rate limits, failover mechanisms, and monitoring.
Governance and management: Enforces security policies and provides centralized visibility into API traffic to detect and respond to potential threats.
The API security landscape
APIs power modern applications, enabling integration between services and data exchange across distributed environments. As cloud computing, microservices, and IoT systems evolve, API security has become increasingly complex and essential.
API security practices include:
Authentication: Verifying the identity of systems and users accessing APIs, using protocols like OAuth 2.0, JWT, and mutual TLS (mTLS)
Authorization: Defining granular access controls for authenticated users, applying role-based access control (RBAC), attribute-based access control (ABAC), and OAuth scopes
Monitoring: Continuously analyzing API activity to detect anomalies, potential breaches, and unauthorized access
Data protection: Encrypting data using TLS 1.3 for transport and implementing field-level encryption to safeguard sensitive data
API hardening: Implementing measures to strengthen API security and reduce vulnerabilities
With the growing adoption of multi-cloud architectures and third-party integrations, API cybersecurity strategies must address increased attack surfaces and operational complexity. Implementing API management platforms (e.g., Kong, Apigee, MuleSoft) and API gateways helps enforce consistent security policies across diverse environments.
Standards and guidelines for API security
Organizations developing API security strategies should align with established frameworks and industry standards:
OWASP API Security Top 10 (2023): Identifies the most critical API-specific vulnerabilities, including broken object level authorization (BOLA), broken authentication, and server-side request forgery (SSRF)
NIST SP 800-204: Provides microservices API security guidelines tailored to multi-cloud and SaaS environments
NIST SP 800-207: Outlines Zero Trust principles that apply to API security, emphasizing continuous verification and least privilege access
ISO/IEC 27001: Includes controls relevant to API security as part of broader information security management systems (ISMS)
Shifting boundaries in API security
As organizations embrace hybrid work models, BYOD policies, and multi-cloud infrastructures, the distinction between internal and external APIs has blurred. This shift has led to a shared responsibility model where security teams and developers collaborate to protect APIs from emerging threats. Zero Trust principles further reinforce the need for consistent authentication, authorization, and data protection across all API requests, regardless of origin.
Zero Trust and API security
Zero Trust principles mandate that every API request be treated as potentially malicious, regardless of the source. This approach eliminates the distinction between “internal” and “external” requests, enforcing continuous verification and least privilege access.
Zero Trust API security practices include:
Authentication and authorization for every request, using OAuth 2.0 with PKCE, OpenID Connect, or mTLS
Input validation and payload inspection to mitigate injection attacks and data tampering
Rate limiting to prevent resource exhaustion and denial of service attacks
Continuous monitoring to detect anomalous patterns that indicate malicious activity
API security in multi-cloud environments
Managing APIs across multi-cloud and hybrid environments introduces significant security challenges. Distributed architectures increase API endpoints, data flows, and potential attack vectors. Security teams must adopt API gateways and management platforms to enforce consistent security policies and monitor API traffic across cloud environments.
Key multi-cloud API security requirements:
Deploy API gateways to centralize policy enforcement, monitoring, and threat detection
Implement API management platforms for centralized visibility and governance
Encrypt data in transit using TLS 1.3 and field-level encryption
Apply rate limiting, circuit breakers, and failover mechanisms to prevent service disruptions
Why APIs are prime attack vectors
APIs are targets for attackers seeking to exploit application vulnerabilities.
Common threats include:
Excessive data exposure: APIs unintentionally return sensitive data in responses due to improper filtering.
Injection attacks: Malicious inputs exploit query parameters, headers, or payload vulnerabilities.
Inadequate authorization: Insufficient access controls allow unauthorized users to access restricted endpoints.
Unsecured endpoints: Unprotected endpoints allow attackers to exfiltrate data or manipulate services.
Why API security matters now more than ever
Many organizations leverage APIs to integrate and establish communication pathways between internal and third-party services across spatial boundaries (on-premises, multiple clouds) and logical boundaries (microservices). Without proper API protection mechanisms, these critical interfaces are vulnerable to denial-of-service attacks and data breaches.
Vulnerable APIs create considerable risks that vary by sector:
Financial services: APIs powering payment processing and account management require rigorous security to prevent fraud and maintain regulatory compliance.
Healthcare: Patient data accessed through APIs requires protection to ensure HIPAA compliance and patient privacy.
E-commerce: APIs handling transaction data and customer information must be secured to maintain consumer trust and prevent revenue loss.
Manufacturing: Industrial APIs controlling production systems need protection from threats that could impact physical operations.
Types of API security
Aspect | REST API security | SOAP API security | GraphQL API security |
Protocol | HTTP/HTTPS | XML over HTTP | Query language over HTTP |
Key security features | Token-based auth, HTTPS, stateless validation | WS-Security, XML encryption, SAML | Query analysis, depth limiting |
Primary strengths | Simplified architecture, widespread adoption | Built-in security standards, strict validation | Flexible data retrieval, single endpoint |
Security challenges | Resource protection, stateless nature | Complexity, performance overhead | Query-based attacks, resource exhaustion |
Best for | Modern web applications, mobile apps | Enterprise environments with stringent security standards | Frontend-driven applications requiring data flexibility |
REST API security
Representational state transfer (REST) APIs require specific security approaches. REST API security focuses on protecting stateless communication using HTTP methods (GET, POST, PUT, DELETE) and resource-oriented URLs. REST API security practices include:
Token-based authentication: REST APIs typically rely on JWT or OAuth tokens over session-based authentication.
HTTPS implementation: All REST API communications must use TLS/SSL encryption.
Stateless validation: Each request must contain all authentication information since REST doesn't maintain session state.
Resource-based permissions: Access controls must align with REST resource-oriented architecture.
Cache controls: Proper HTTP headers prevent sensitive data from being cached.
REST APIs benefit from their simplified architecture but require careful implementation of authentication mechanisms and resource protection to prevent common vulnerabilities, including broken object level authorization (BOLA).
SOAP API security
Simple object access protocol (SOAP) APIs provide built-in security standards that offer advantages for enterprise applications. SOAP security features include:
WS-security framework: Provides standardized approaches to message integrity, confidentiality, and authentication
XML encryption: Enables granular encryption of specific XML elements within SOAP messages
SAML integration: Supports federated authentication through security assertion markup language (SAML)
Strict schema validation: XML schemas enforce strict message validation
Built-in error handling: Standardized fault handling improves security response
While less common in new applications, SOAP APIs continue to serve crucial roles in enterprise environments where comprehensive security standards and guaranteed delivery are essential. Organizations maintaining SOAP APIs benefit from these built-in security features but must manage their increased complexity and performance overhead.
GraphQL API security
Due to their flexible query structure, GraphQL APIs present unique security challenges. Unlike REST APIs with fixed endpoints, GraphQL typically exposes a single endpoint where clients can request precisely the data they need. GraphQL security considerations include:
Query complexity analysis: Preventing resource exhaustion from complex nested queries
Depth limiting: Restricting how deeply nested a query can be to prevent denial of service attacks
Result limiting: Controlling the size and quantity of data that a single query can return
Persisted queries: Using pre-registered queries rather than accepting arbitrary queries
Field-level permissions: Implementing granular access controls for each queryable field
GraphQL APIs require specialized security approaches beyond traditional API security patterns. Their flexibility offers advantages for frontend developers but introduces challenges for security teams monitoring and controlling data access. Comprehensive GraphQL security requires standard API security controls and GraphQL-specific protections against query-based attacks.
Fundamental API security concepts
Authentication: Verifying identity
Authentication addresses the fundamental question: “Who or what is making this API request, and can we verify it as legitimate?” Effective API security implementation begins with strong authentication, ensuring only legitimate users and systems can access your interfaces through properly secured API endpoints.
In a Zero Trust approach to API security, developers must validate two distinct identities in every API communication: the software calling the API and the end user of that software. For instance, API keys typically identify the calling software, while OAuth bearer tokens identify the end user. Modern API security solutions implement multiple authentication factors to ensure complete verification.
Today’s API developers increasingly adopt enhanced authentication protocols to address evolving threats. For example, security experts recommend Proof Key for Code Exchange (PKCE) for OAuth 2.0 implementations to prevent authorization code interception attacks. Organizations can enhance API security by integrating multi-factor authentication (MFA) into API authentication flows for sensitive operations, while implementing mutual TLS (mTLS), which provides stronger security for machine-to-machine communications than traditional API keys.
Authorization: Controlling access
Authorization focuses on the critical question: "What actions can the authenticated entity perform, and on which resources?" After completing identity verification, API security systems determine the precise extent of access granted to the authenticated entity.
Role-based access control (RBAC) and Attribute-based access control (ABAC) have become prominent models for defining API security access policies. However, OAuth 2.0 scopes are the most commonly implemented authorization mechanism specifically for APIs in modern implementations. These combined approaches enable organizations to implement granular access management tailored to user roles, data attributes, and specific API operations, addressing key vulnerabilities identified in the OWASP API Security Top 10.
Data protection and validation
Effective API security requires validating each request against the API schema, verifying that all expected fields are present, correctly formatted, and free from unexpected or malicious data. Even when inputs pass basic validation, comprehensive API security solutions implement additional security checks to verify they contain no malicious payloads that could exploit vulnerabilities.
Schema validation tools and libraries have become essential components for preventing injection attacks. Organizations implementing strict validation protocols reduce the risk of malicious payloads compromising vulnerable API endpoints and prevent distributed denial of service attacks targeting validation weaknesses.
Resource protection
APIs consume computing resources to serve requests and often impact external systems or real-world operations. While normal operations require these effects, malicious actors frequently exploit them to launch attacks. As part of a comprehensive API security strategy, organizations can mitigate abuse, prevent denial-of-service attacks, and protect system integrity by implementing rate limiting and continuous usage monitoring.
Common API security vulnerabilities
The OWASP API security top 10
The Open Web Application Security Project (OWASP) API Security Top 10 provides the industry-standard framework for understanding and addressing the most critical API security risks. The 2023 list includes:
ID | Risk | Description | Real-World Impact |
API1:2023 | Broken object level authorization (BOLA) | Attackers manipulate requests to access data objects without proper authorization checks | Unauthorized data access, including customer records and financial information, leads to breaches and regulatory violations |
API2:2023 | Broken authentication | Weak authentication mechanisms enable attackers to compromise tokens or exploit implementation flaws | Account takeovers, session hijacking, and credential stuffing can result in financial loss and reputational damage |
API3:2023 | Broken object property level authorization | APIs inadvertently expose data attributes that should remain restricted, relying on clients to filter sensitive data | Sensitive user data and internal system details may be exposed, increasing the risk of data leaks and unauthorized data mining |
API4:2023 | Unrestricted resource consumption | APIs lack rate limits or quotas, allowing attackers to overwhelm servers with excessive requests | Service disruptions, degraded performance, and increased operational costs due to resource exhaustion |
API5:2023 | Broken function level authorization | Missing function-level authorization checks let attackers access restricted endpoints | Privilege escalation and unauthorized administrative access can lead to data manipulation and potential system breaches |
API6:2023 | Unrestricted access to sensitive business flows | APIs lack protections against automated abuse of business functions, allowing attackers to exploit legitimate functionality at scale | Unauthorized modifications of critical data compromise data integrity and enable privilege escalation |
API7:2023 | Server side request forgery | APIs process user-supplied URLs without validation, allowing attackers to make the server request internal resources inaccessible to the attacker | Unauthorized internal network access, data exposure, and increased risk of internal asset compromise |
API8:2023 | Security misconfiguration | Incomplete or default configurations expose sensitive data and services to attackers | Unauthorized data exposure, unauthorized system access, and easier attack vectors for exploiting known vulnerabilities |
API9:2023 | Improper inventory management | Untracked or deprecated APIs remain accessible, creating potential attack vectors | Unpatched vulnerabilities in legacy or outdated endpoints expand the attack surface and increase the risk of exploitation |
API10:2023 | Unsafe consumption of APIs | APIs consume untrusted or poorly validated data, leading to downstream vulnerabilities | Delayed breach detection, prolonged attacker presence, and increased risk of data exfiltration |
API security implementation
API security implementation requires a multi-layered strategy that addresses authentication, authorization, encryption, monitoring, and incident response.
The API security lifecycle:
Design: Define security requirements, perform threat modeling, and establish governance
Development: Implement secure coding practices, validate API schemas, and conduct code reviews
Deployment: Configure runtime protections, establish monitoring, implement API gateways, and deploy web application firewalls (WAFs) to detect common attack patterns (e.g., SQL injection, cross-site scripting)
Operation: Monitor for threats, respond to incidents, regularly test and validate controls
API security testing methods
API security testing requires multiple methods to assess vulnerabilities thoroughly:
Static analysis (SAST): Analyzes source code for hardcoded credentials, insecure functions, and improper error handling
Dynamic analysis (DAST): Tests running APIs against simulated attacks to identify runtime vulnerabilities
Fuzz testing: Submits random or malformed data to detect parsing errors and crashes
Contract testing: Validates API behavior against OpenAPI or Swagger specifications to identify deviations or unexpected responses
Penetration testing: Identifies business logic flaws and real-world exploitation scenarios through manual testing
Essential API security controls
Discover and inventory all APIs
Identify all APIs using automated discovery tools, including shadow and deprecated endpoints.Implement strong authentication
Deploy OAuth 2.0 with properly signed JWTs (RS256 or ES256) and comprehensive validation controls.Enforce proper authorization
Apply least privilege principles and conduct regular permission audits.Deploy API gateway protection
Centralize security controls through API gateways to enforce consistent policies.Validate inputs and encode outputs
Prevent injection attacks through strict parameter validation and parameterized queries.Encrypt and protect data
Implement TLS 1.3 for transport security, apply field-level encryption for sensitive data, and establish secure key management practices.Monitor and analyze traffic
Deploy behavioral analytics and anomaly detection to identify suspicious patterns, unusual access patterns, and potential attacks.Test and scan regularly
Conduct ongoing API-specific penetration testing and vulnerability scanning.
Complete API protection requires security controls throughout the entire API lifecycle. Development teams should apply pre-runtime protections during design and development (schema validation, security testing), then complement these with runtime protections (request validation, monitoring).
API security frequently asked questions
What are the most common API security risks?
Security vulnerabilities when implementing APIs include:
Authentication and authorization risks
Broken authentication mechanisms exposing credentials
Insufficient authorization checks allowing unauthorized access
Data exposure risks
Excessive data in API responses revealing sensitive information
Inadequate encryption of sensitive data in transit
Resource management risks
Missing rate limits allowing denial of service attacks
Improper API inventory leading to shadow and zombie APIs
Implementation risks
Injection vulnerabilities in API parameters
Security misconfigurations in API deployments
How is API security different from web application security?
While both protect digital assets, API security and web application security focus on different aspects of the technology stack and threat landscape:
API security
Protects direct machine-to-machine communications
Secures structured data exchanges between services
Controls access to backend resources and databases
Emphasizes authentication between systems and services
Web application security
Protects user-facing interfaces and interactions
Secures browser-based sessions and state management
Defends against browser-specific attacks like XSS and CSRF
Emphasizes human user authentication and activity monitoring
What authentication methods are used for APIs?
API authentication varies depending on security requirements:
Basic authentication methods
API keys for simple identification
Basic authentication for straightforward use cases
Token-based authentication
JWT tokens provide signed identity information
OAuth 2.0 enables delegated authorization
OpenID Connect for standardized authentication flows
Advanced authentication methods
Certificate-based authentication (including mutual TLS) for secure machine-to-machine connections
MFA for high-security operations
Mutual TLS for encrypted bidirectional authentication
How is rate limiting implemented for API security?
Rate limiting protects API availability and prevents abuse by controlling request volumes:
Implementation approaches
Request counting per user, application, or endpoint
Time-based windows (per second, minute, hour)
Incremental backoff for repeated violations
Technical controls
HTTP 429 responses for exceeding limits
Request queuing for traffic smoothing
Different thresholds based on the authentication level
Deployment strategies
Gateway-level limits for broad protection
Service-level limits for specific endpoint protection
Distributed rate limiting for large-scale deployment
Simplify API security with centralized authorization management
Streamline policy creation and enforcement across all your APIs. Implement OAuth 2.0 and modern authorization frameworks without the complexity, while giving developers more time to focus on building great applications.
