What is API Gateway Security?
API Gateway Security acts as a centralized, front-line defense for microservices, providing essential protection such as authentication (OAuth/JWT), authorization, rate limiting, and threat protection against attacks like DDoS and SQL injection. It acts as a unified entry point, enforcing consistent security policies and logging traffic before requests reach backend services.
Key API gateway security functions:
- Authentication and authorization: Validates user identity using OAuth 2.0, OpenID Connect, API keys, or mTLS, ensuring only authorized clients access specific resources.
- Rate limiting and throttling: Controls traffic volume to prevent denial-of-service (DoS) attacks and ensure system stability.
- Encryption in transit: Enforces HTTPS/TLS to protect data integrity and confidentiality between the client and the gateway.
- Web application firewall (WAF) and validation: Inspects incoming payloads for malicious content, such as injection attacks (SQL, XSS), and validates against API schemas.
- Logging and monitoring: Records all transactions to provide audit trails, analytics, and visibility into security events.
In this article:
A secure API gateway sits at the edge of the system and handles incoming traffic, making it a high-value target. Weaknesses at this layer can expose multiple backend services at once:
- Centralized protection: The gateway enforces security policies in one place.
- Prevents unauthorized access: Strong authentication and authorization at the gateway stop invalid or malicious requests before they reach internal systems.
- Mitigates common attacks: Gateways can block threats like injection attacks, credential stuffing, and distributed denial-of-service attacks using rate limiting and filtering.
- Protects sensitive data: Data masking, encryption, and validation at the gateway reduce the risk of leaking sensitive information.
- Improves visibility and monitoring: Logging and analytics at the gateway provide insight into traffic patterns, anomalies, and potential threats.
- Simplifies security management: Updating policies at the gateway is faster than changing multiple backend services.
- Supports compliance requirements: Centralized controls and audit logs help meet regulatory standards such as GDPR, HIPAA, and PCI DSS.
- Reduces backend load: By filtering bad traffic early, the gateway prevents unnecessary strain on internal services.
Broken Authentication
Broken authentication occurs when the API gateway fails to verify the identity of clients or users. This can happen due to weak credential management, flawed token validation, or improper session handling. Attackers exploit these weaknesses to impersonate legitimate users and gain unauthorized access to sensitive data or functions. Inadequate authentication at the gateway level can undermine the security of connected backend services.
APIs often rely on tokens, API keys, or OAuth mechanisms for authentication. If these methods are not securely implemented or validated, attackers may reuse stolen credentials, predict tokens, or exploit session fixation vulnerabilities.
How to address:
Addressing broken authentication requires strong credential management, secure token handling, and regular reviews of authentication flows.
Broken Object Level Authorization
Broken object level authorization arises when the API gateway does not enforce access control over specific resources or objects. Attackers can exploit this by manipulating requests to access or modify data they are not authorized to interact with. This risk increases in APIs that expose object identifiers in URLs or payloads without verifying the requester's permissions. The lack of fine-grained authorization checks enables attackers to enumerate or tamper with data belonging to other users or systems.
How to address:
To reduce this risk, API gateways must enforce strict authorization policies at the object level, verifying that each requester has permission to access or modify the targeted resource. Regular audits and security testing help identify authorization gaps.
Excessive Data Exposure
Excessive data exposure occurs when the API gateway returns more data than necessary in responses. This often results from backend services sending full objects while the gateway fails to filter out sensitive or irrelevant fields before forwarding the data to clients. Attackers can exploit this to collect confidential information such as internal identifiers, configuration details, or personal data.
How to address:
API gateways should expose only the minimum data required by clients, applying response filtering and data masking where appropriate. Reviewing response schemas and conducting security assessments can help identify overexposed data. Minimizing data exposure reduces the risk of sensitive information leakage.
Rate Limit Abuse and DDoS Attempts
APIs are vulnerable to rate limit abuse and distributed denial-of-service (DDoS) attacks when gateways do not control the volume of incoming requests. Attackers can overwhelm backend services by sending excessive requests, consuming resources, and causing legitimate traffic to be dropped or delayed. This impacts availability and can cause financial and reputational damage.
How to address:
Implementing rate limiting and throttling at the API gateway helps reduce these risks by enforcing request quotas and detecting abnormal traffic patterns. Gateways should integrate with DDoS protection services and provide real-time monitoring to identify and block abusive clients. Regular testing and tuning of rate limits help balance user experience and security.
Injection and Malicious Payloads
Injection attacks occur when malicious data is sent through the API gateway to backend services, exploiting insufficient input validation. Common types include SQL injection, command injection, and script injection. Attackers use these techniques to execute unauthorized commands, access sensitive data, or disrupt service operations.
How to address:
API gateways must enforce strict input validation and sanitization to prevent malicious payloads. Integrating with a web application firewall (WAF) and using schema validation can help detect and block injection attempts before they reach backend systems. Regular security assessments and updates to validation logic help address new attack vectors.
Uri Dorot
Uri Dorot is a senior product marketing manager at Radware, specializing in application protection solutions, service and trends. With a deep understanding of the cyber threat landscape, Uri helps companies bridge the gap between complex cybersecurity concepts and real-world outcomes.
Tips from the Expert:
In my experience, here are tips that can help you better secure and operationalize API gateways:
1. Treat the gateway as a policy enforcement point, not the only security layer: Backend services must still validate authentication, authorization, and input. Attackers often bypass gateways through internal routes, forgotten endpoints, or misconfigured services.
2. Separate north-south and east-west gateway policies: Internet-facing APIs and internal service traffic have different trust assumptions, latency needs, and threat models. Avoid reusing identical policies everywhere.
3. Prevent "gateway drift" across environments: Staging, regional, and emergency deployments often run weaker policies than production. Continuously compare configurations to detect disabled WAF rules, missing scopes, or inconsistent rate limits.
4. Validate JWT claims at the gateway and downstream: The gateway should verify signatures, issuer, audience, expiration, and scopes, but sensitive services should still validate critical claims independently.
5. Use adaptive rate limiting instead of static quotas: Attack patterns evolve dynamically. Adjust thresholds based on user behavior, endpoint sensitivity, token reputation, and real-time risk scoring.
1. Authentication and Authorization
Authentication and authorization ensure that only verified and permitted users or systems can access backend services. Authentication verifies the identity of a requester using mechanisms like API keys, OAuth tokens, or certificates, while authorization determines what actions or data the authenticated user can access. The gateway acts as a centralized enforcement point, supporting consistent access control across APIs.
A strong authentication and authorization setup blocks unauthorized access and supports auditing and compliance by logging access attempts and enforcing least privilege. Proper implementation reduces the attack surface and helps prevent privilege escalation or unauthorized data manipulation. Regular reviews and updates are necessary as user roles, applications, and threats change.
2. Rate Limiting and Throttling
Rate limiting and throttling help maintain API availability and protect backend resources from abuse. Rate limiting sets a maximum number of requests that clients can make in a given time period, while throttling controls the rate of requests to smooth traffic spikes. These mechanisms help prevent overload from legitimate users and deliberate abuse.
API gateways implement these controls by tracking client request patterns and enforcing defined limits, returning error responses when limits are exceeded. Tuning rate limits based on user roles, endpoints, and usage patterns helps balance usability and security.
3. Encryption in Transit
Encryption in transit protects data as it moves between clients, the API gateway, and backend services. This is typically achieved using protocols like TLS, which encrypt requests and responses to prevent interception or tampering. Without encryption, sensitive data such as credentials, tokens, or personal information can be exposed to man-in-the-middle attacks.
API gateways enforce encryption by requiring HTTPS and managing certificates. They may also support mutual TLS (mTLS) for stronger client and server authentication. Updating cryptographic libraries and protocols helps maintain protection against emerging threats. Encryption in transit is a baseline requirement for API security and regulatory compliance.
4. Web Application Firewall (WAF) and Validation
A web application firewall (WAF) inspects API traffic for known attack patterns, blocking malicious requests before they reach backend systems. Combined with input validation, the gateway can detect and reject requests containing malicious payloads, malformed data, or policy violations. WAF rules are updated to address new threats.
Input validation at the gateway enforces expected formats, data types, and value ranges, preventing injection and data corruption attacks. Centralizing validation and WAF functions at the gateway allows consistent protection and reduces the risk of vulnerabilities reaching backend services. Regular testing and tuning of WAF rules and validation schemas help maintain protection.
5. Logging and Monitoring
Logging and monitoring support detection, investigation, and response to API security incidents. API gateways generate logs for requests, including authentication attempts, errors, and policy violations. These logs provide visibility into usage patterns and anomalous behavior.
Continuous monitoring enables real-time alerting and automated responses, such as blocking suspicious clients or escalating incidents to security teams. Integrating API gateway logs with SIEM (security information and event management) systems supports threat detection and compliance reporting. Effective logging and monitoring support incident response.
Organizations should consider these practices to improve security when using an API gateway.
1. Use Mutual TLS (mTLS)
Mutual TLS (mTLS) requires both the client and the server to authenticate each other using digital certificates during the TLS handshake. This ensures that only trusted clients can communicate with the API gateway. mTLS is especially useful for internal service-to-service communication within microservices architectures.
To implement mTLS:
- Manage and rotate certificates.
- Configure gateways and clients to validate certificates.
- Monitoring certificate status for expiration or revocation.
While mTLS adds operational complexity, it strengthens authentication and confidentiality where required.
2. Apply Fine-Grained Access Control
Fine-grained access control ensures that users and systems can perform specified actions on specified resources. Instead of broad permissions, the API gateway enforces policies based on roles, scopes, attributes, or context such as IP address or device. This reduces over-privileged access and limits the impact of compromised credentials.
To implement granular access control:
- Define clear access policies.
- Mapping these policies to endpoints and methods.
- Integrate gateways with identity providers to evaluate tokens and enforce scopes.
- Use attribute-based access control (ABAC) with dynamic conditions such as time of access or request origin.
3. Use Short-Lived Tokens
Short-lived tokens reduce the window of opportunity for attackers if a token is leaked or stolen. Limiting token lifespan to minutes or hours forces frequent re-authentication or token refresh. API gateways should validate token expiration and reject expired tokens. They often integrate with identity providers to support secure refresh flows, allowing users to obtain new tokens without repeatedly exposing credentials.
Combining short-lived tokens with rotating refresh tokens adds another layer of defense. If a refresh token is compromised, rotation prevents indefinite reuse. This approach balances usability and session security.
To implement short-lived tokens:
- Configure access tokens to expire within minutes or hours based on risk requirements.
- Use secure refresh token flows with refresh token rotation and revocation capabilities.
- Validate token expiration, issuer, audience, and scopes at the API gateway for every request.
4. Regularly Rotate API Keys
API keys that remain static for long periods are a common attack vector. Regular rotation limits exposure if a key is leaked and ensures compromised keys become unusable after a defined period. Gateways should support automated key rotation and allow multiple active keys during transition periods to avoid service disruption.
Monitoring key usage is also important. Unusual patterns, such as spikes in traffic or access from new locations, can indicate compromise. Immediate revocation and regeneration of affected keys should be part of the response process.
To ensure proper key management:
- Automate API key rotation on a defined schedule and enforce expiration policies.
- Monitor key usage for unusual activity, geographic anomalies, or traffic spikes.
- Support rapid key revocation and replacement through centralized key management processes.
5. Sanitize and Validate Inputs
Input validation prevents malformed or malicious data from reaching backend services. The API gateway should enforce strict schemas, data types, and value constraints for incoming requests. Sanitization removes or neutralizes harmful content, reducing the risk of injection attacks. This includes stripping unexpected characters, normalizing inputs, and rejecting payloads that do not match expected formats.
Combining schema validation with a WAF provides layered protection. Validation rules should evolve alongside the API to ensure new fields and endpoints are covered. Consistent enforcement at the gateway reduces reliance on backend validation alone.
To implement input sanitization and validation:
- Enforce request schemas, data types, field lengths, and allowed values at the gateway.
- Sanitize inputs to remove unexpected characters and potentially malicious content.
- Reject malformed requests and log validation failures for monitoring and investigation.
6. Discover and Inventory All APIs
Untracked or undocumented APIs, often called shadow APIs, create security blind spots. Maintaining a complete inventory ensures exposed endpoints are known, monitored, and protected by the gateway. Automated discovery tools can scan traffic, code repositories, and infrastructure to identify unmanaged APIs and detect deprecated endpoints that remain accessible.
Keeping an up-to-date catalog allows teams to apply consistent security policies, enforce versioning, and retire unused APIs. This reduces the overall attack surface and improves governance across the API lifecycle.
To implement a complete API inventory:
- Use automated discovery tools to identify exposed, undocumented, and shadow APIs.
- Maintain a centralized catalog of APIs, versions, owners, and security requirements.
- Regularly review and retire deprecated or unused endpoints to reduce attack surface.
7. Protect Against Business Logic Abuse
Business logic abuse occurs when attackers exploit valid API workflows in unintended ways, such as bypassing limits or manipulating sequences of calls. These attacks often use legitimate requests. API gateways can reduce this risk by enforcing behavioral rules, such as sequence validation, workflow-based rate limits, and anomaly detection.
To prevent abuse:
- Restrict how often sensitive operations can be performed within a session.
- Monitor usage patterns over time to identify anomalies.
- Integrate with analytics and fraud detection systems to support detection and response to logic abuse that bypasses traditional controls.
8. Add Bot Protection for API Traffic
Automated bots can abuse APIs for scraping, credential stuffing, or denial-of-service attacks. Basic rate limiting is often insufficient to distinguish between legitimate users and bots. Bot protection mechanisms analyze behavior, request patterns, and signals such as device fingerprints to identify non-human traffic. Machine learning models can improve detection by adapting to changing bot techniques.
Integrating bot management with the API gateway enables real-time responses such as blocking, rate limiting, or issuing challenges. This preserves backend resources and supports fair usage for legitimate clients.
To implement short-lived tokens:
- Analyze request behavior, device fingerprints, and traffic patterns to distinguish bots from legitimate users.
- Apply adaptive rate limiting, blocking, or challenge mechanisms for suspicious traffic.
- Integrate bot detection with security analytics and threat intelligence platforms for continuous monitoring.
Securing the API gateway is only effective when it is paired with protection that follows your APIs wherever they run. Radware API Security continuously discovers and protects your APIs and business logic in real time as part of Radware's Cloud Application Protection Service. Using AI-based analysis, it automatically discovers API endpoints, learns each API's business logic, and generates accurate policies so APIs are protected against sophisticated, AI-driven attacks while staying compliant with PCI DSS 4.
Key capabilities of Radware API Protection:
- Automated API discovery: Finds API endpoints and undocumented changes, then generates tailored security policies to eliminate the blind spots created by shadow and undocumented APIs.
- Business logic attack prevention: Continuously learns from real-time transactions and stops business logic attacks as they occur, automatically and accurately.
- Positive security model: Validates requests against the defined API schema and scans for embedded attacks before they reach backend services.
- Bot and account takeover protection: Blocks bad bot and ATO activity targeting APIs, such as credential stuffing and scraping.
- Data leakage prevention: Inspects API responses and masks sensitive data such as credit card numbers and PII to prevent excessive data exposure.
- API quotas: Limits the number of API calls per timeframe, per endpoint, and per source to prevent abuse and rate-limit-based attacks.
- API DDoS protection: Mitigates API DDoS attacks by automatically generating accurate attack signatures in real time.
- Consistent security everywhere: Enforces consistent, architecture-agnostic protection across any environment as part of Cloud Application Protection Services.
- PCI DSS 4 compliance: Addresses the requirement to detect and protect against business logic vulnerability-based attacks.