API Endpoint Security: 10 Risks, Key Controls & Best Practices

• Strong API authentication: Verifies users, applications, and services before allowing access to protected endpoints.
• Fine-grained authorization: Restricts access to individual functions, objects, and resources based on roles, scopes, ownership, or other attributes.
• API schema and request validation: Rejects requests with unexpected methods, parameters, data types, values, or payload structures.
• Rate limiting and throttling: Controls request frequency, quotas, and concurrency to reduce abuse and resource exhaustion.

• Encryption in transit: Uses TLS to protect API requests and responses as they travel between clients, gateways, and services.
• API gateway security: Centralizes controls such as authentication, token validation, rate limiting, routing, and security logging.
• Web application and API protection (WAAP): Inspects traffic for injection, malformed requests, reconnaissance, and other API threats.
• Bot and automated abuse protection: Detects and controls credential stuffing, scraping, account enumeration, fake account creation, and other automated attacks.

• What are the Most Common API Endpoint Security Risks?
• How Does API Endpoint Security Work?
• Key API Endpoint Security Controls

• API Endpoint Security Best Practices
• Securing API Endpoints with Radware API Security Service

Broken Object Level Authorization (BOLA)

BOLA occurs when an API accepts an object identifier but does not verify that the authenticated user is allowed to access that specific object. For example, an endpoint such as /orders/1234 might return an order based only on its ID. If changing the ID to 1235 exposes another customer's order, the endpoint has an object-level authorization flaw.

Authentication alone does not prevent BOLA because the attacker may be a legitimate user. APIs must check ownership, tenant boundaries, roles, or other authorization rules whenever an operation accesses an object. These checks should apply to read, update, and delete operations rather than relying on identifiers being difficult to guess.

Broken Authentication

Broken authentication occurs when weaknesses in identity or session controls allow attackers to impersonate users. Problems can include weak credential policies, insecure password recovery, predictable or long-lived tokens, missing token validation, and credentials exposed in URLs or logs. Credential stuffing can also compromise accounts when APIs do not limit repeated login attempts.

Protected endpoints should validate authentication credentials or tokens on every request. Tokens should have appropriate expiration periods and be checked for properties such as issuer, audience, and signature where applicable. Sensitive authentication operations should also use rate limiting and stronger controls such as multi-factor authentication when the risk warrants it.

Broken Function Level Authorization

Broken function level authorization occurs when an API does not verify whether a user has permission to execute a particular operation. A normal user might discover an administrative endpoint such as /admin/users and successfully call it even though the application's interface never displays that function.

Hiding endpoints or buttons in the client does not provide authorization because clients can send API requests directly. Each sensitive operation should perform server-side permission checks based on the authenticated identity and required role or privilege. APIs should also deny access by default when no explicit authorization rule applies.

Broken Object Property Level Authorization (BOPLA)

Broken object property level authorization occurs when an API exposes or accepts object properties that a user should not be permitted to access or modify. For example, a user profile endpoint might return internal fields such as account status or permissions, or allow a client to change a property such as role by adding it to an update request.

APIs should explicitly define which properties each operation and user type can read or modify. Response filtering can prevent sensitive fields from being exposed, while allowlists for writable fields can block unauthorized property changes. APIs should not rely on clients to omit protected fields or assume that undocumented properties cannot be discovered.

Injection Attacks

Injection attacks occur when untrusted API input reaches a database, command interpreter, template engine, or another parser without safe handling. Depending on the backend technology, attackers may attempt SQL injection, NoSQL injection, operating system command injection, or similar attacks.

Input validation helps reject values that do not match expected formats, but it should not be the only defense. Database operations should use parameterized queries or equivalent safe interfaces, and applications should avoid constructing commands from raw input. Backend accounts should also receive only the permissions they need, limiting the impact of a successful injection.

API Abuse and Automated Attacks

Attackers can automate valid API functions at a scale or frequency that the application did not intend. Examples include credential stuffing, account enumeration, mass account creation, content scraping, inventory hoarding, spam, and repeated attempts to exploit promotional or business workflows.

Traditional security checks may not block these requests because each individual call can be syntactically valid. APIs can combine rate limits, quotas, behavioral analysis, bot detection, and monitoring to identify suspicious patterns. Controls should consider user accounts, API keys, devices, and other signals rather than relying only on IP addresses.

Related content: Read our article about API abuse.

Unrestricted Access to Sensitive Business Flows

Unrestricted access to sensitive business flows occurs when an API exposes legitimate operations without controls that prevent automated or excessive use. Attackers may exploit workflows such as purchasing limited inventory, reserving appointments, submitting referrals, creating accounts, or redeeming promotional offers at a scale that harms the business or other users.

Protecting these flows requires controls based on how the operation is expected to be used. APIs can enforce transaction limits, quotas, velocity checks, and workflow-specific rules, while monitoring for abnormal automation patterns. High-risk actions may also require additional verification or human interaction when automated abuse is detected.

Unrestricted Resource Consumption

API operations can consume CPU, memory, network bandwidth, storage, database connections, or paid third-party services. An attacker can exploit endpoints that permit large payloads, expensive searches, unlimited pagination, excessive file uploads, or large numbers of concurrent requests.

APIs should set limits according to the cost of each operation. Relevant controls include request and response size limits, pagination boundaries, execution timeouts, upload restrictions, rate limits, and concurrency limits. Monitoring resource usage can also reveal endpoints whose normal-looking requests create disproportionate backend workloads.

Security Misconfiguration

Security misconfiguration covers insecure settings in API servers, frameworks, gateways, cloud services, and supporting infrastructure. Examples include overly permissive cross-origin resource sharing, verbose error messages, unnecessary HTTP methods, default credentials, exposed debugging interfaces, weak TLS settings, and publicly reachable management endpoints.

Configuration should follow a documented secure baseline across development, testing, and production environments. Automated configuration and infrastructure scanning can identify deviations from that baseline. Teams should also remove unused features and restrict administrative interfaces because every unnecessary service or capability increases the attack surface.

Shadow and Zombie APIs

Shadow APIs are endpoints that operate outside the organization's approved inventory or security processes. They can appear when development teams deploy services independently, create temporary endpoints, or bypass normal API management. Because security teams may not know these APIs exist, they may receive inadequate testing, monitoring, or access controls.

Zombie APIs are outdated endpoints or API versions that remain accessible after they are supposedly retired. They may contain vulnerabilities already fixed in newer versions. API discovery, centralized inventory management, version tracking, and traffic monitoring can help identify both types, while a defined decommissioning process ensures obsolete endpoints are actually disabled.

Step 1: API Discovery and Inventory

Security starts with knowing which API endpoints are accessible. API discovery identifies endpoints across:

• Gateways
• Application environments
• Cloud infrastructure
• Network traffic

The resulting inventory should record information such as API versions, owners, authentication requirements, exposed operations, and data sensitivity. Maintaining this inventory also helps identify shadow and zombie APIs. Teams can compare discovered endpoints with approved specifications and deployment records to find undocumented or obsolete services. The inventory should be updated as APIs are added, changed, and retired.

Step 2: Authentication and Identity Verification

Authentication establishes the identity of a user, service, or application making an API request. Depending on the architecture, APIs can use mechanisms such as:

• API keys
• OAuth 2.0 access tokens
• OpenID Connect
• Signed tokens
• Mutual TLS

The API must validate credentials before allowing access to protected resources. Token-based systems may need to verify signatures, expiration times, issuers, audiences, and scopes. Credentials should also be transmitted over TLS and protected from exposure in source code, URLs, and logs.

Step 3: Authorization and Access Control

After authentication, authorization determines what the verified identity can do. The API evaluates permissions based on factors such as:

• Roles
• Scopes
• Ownership
• Tenant membership
• Attributes associated with the user and requested resource

Authorization checks should occur on the server for every protected operation and object. For example, permission to call an order endpoint does not automatically mean a user can access every order. This distinction helps prevent both object-level and function-level authorization vulnerabilities.

Step 4: Request Validation

Request validation checks whether incoming data conforms to what the endpoint expects before the data reaches application logic. APIs can validate:

• HTTP methods
• Content types
• Headers
• Parameter types
• Allowed values
• Payload sizes
• Request body schemas

Validation should reject malformed or unexpected input rather than attempting to process it. However, validation does not replace context-specific protections such as parameterized database queries. Both are needed to reduce injection risks and prevent unexpected input from reaching sensitive backend components.

Step 5: Traffic Inspection and Threat Detection

API gateways, web application firewalls, and dedicated API security controls can inspect traffic for signs of attacks. They can identify patterns associated with:

• Injection attempts
• Malformed requests
• Credential attacks
• Reconnaissance
• Access to prohibited endpoints

Detection becomes more effective when it considers behavior across multiple requests. A single request might appear legitimate, while hundreds of similar requests across accounts or resources can indicate enumeration or automated abuse. Detection systems can alert security teams or block traffic according to configured policies.

Step 6: Rate Limiting and Abuse Prevention

Rate limiting controls how frequently clients can call an endpoint within a defined period. Limits can be applied by identifiers such as:

• Account
• API key
• Token
• IP address
• Endpoint

More resource-intensive operations can have stricter limits than inexpensive requests. Abuse prevention goes beyond simple request counts. APIs can enforce quotas, concurrency limits, payload limits, and restrictions on sensitive workflows such as login or password recovery. These controls help reduce credential attacks, scraping, denial-of-service attempts, and excessive consumption of backend resources.

API logging records security-relevant events such as:

• Authentication failures
• Authorization denials
• Endpoint access
• Validation errors
• Administrative actions
• Unusual request volumes

Logs should contain enough context for investigation without recording passwords, access tokens, or other sensitive secrets. Continuous monitoring analyzes these events to detect changes in API behavior and emerging attacks. Security teams can establish alerts for patterns such as repeated access failures, unexpected traffic spikes, or calls to deprecated endpoints. Logs also support incident investigation, auditing, and improvement of security policies.

Strong API Authentication

Strong authentication ensures that protected endpoints accept requests only from verified users, applications, or services. Common approaches include OAuth 2.0 access tokens, OpenID Connect for user identity, API keys for defined application use cases, and mutual TLS for service-to-service authentication.

Authentication mechanisms should use short-lived credentials where practical and validate tokens completely, including signatures, expiration, issuer, and audience. Secrets and API keys should be stored securely, rotated when necessary, and never embedded in public client code or exposed through URLs and logs.

Fine-Grained Authorization

Fine-grained authorization determines which resources and operations an authenticated identity can access. Policies can use roles, scopes, resource ownership, tenant membership, or other attributes to make access decisions.

Checks should occur at both the function and object level. For example, permission to use an /accounts endpoint should not automatically grant access to every account record. Server-side authorization must be enforced for each sensitive request instead of relying on restrictions implemented in the client.

API Schema and Request Validation

Schema validation checks incoming requests against the API's expected structure. An OpenAPI or similar specification can define permitted paths, HTTP methods, parameters, data types, required fields, and acceptable values.

Requests that do not conform to the expected schema should be rejected before reaching sensitive application logic where possible. Applications should also enforce size and format restrictions and safely process accepted values. Schema validation reduces malformed input but does not replace parameterized queries or other injection defenses.

Rate Limiting and Throttling

Rate limiting restricts how many requests a client can make during a given period. Limits can apply by endpoint, user, token, API key, IP address, or another identity. Sensitive or computationally expensive endpoints often require stricter limits.

Throttling can slow requests when clients approach or exceed configured thresholds rather than immediately blocking all traffic. Quotas and concurrency controls provide additional protection. Together, these mechanisms help contain credential attacks, scraping, resource exhaustion, and accidental traffic spikes.

Encryption in Transit

Encryption in transit protects API requests and responses while they travel between clients, gateways, services, and other infrastructure. APIs should use HTTPS with properly configured TLS to prevent network observers from reading or modifying sensitive traffic.

TLS should be enforced rather than offered as an optional connection method. Certificate validation and modern protocol configurations are also important. For high-trust service-to-service environments, mutual TLS can additionally authenticate both sides of a connection.

API Gateway Security

An API gateway provides a centralized enforcement point between clients and backend API services. It can handle functions such as authentication, token validation, rate limiting, routing, request size restrictions, TLS termination, and security logging.

Centralized enforcement helps teams apply consistent baseline controls across many endpoints. However, gateway protection does not replace security inside the application. Backend services still need object-level authorization, business logic validation, and controls for threats that require application context.

Web Application and API Protection (WAAP)

WAAP platforms combine controls for web applications and APIs, commonly including web application firewall capabilities, API protection, bot management, and denial-of-service defenses. They inspect incoming traffic and can block requests matching known attack patterns or configured security policies.

For APIs, WAAP can complement gateway controls by detecting threats such as injection attempts, reconnaissance, malformed traffic, and suspicious usage patterns. Effective deployment requires policies that reflect actual API behavior so that malicious traffic is blocked without disrupting legitimate clients.

Bot and Automated Abuse Protection

Bot protection addresses automated activity that may use technically valid API requests for malicious purposes. Examples include credential stuffing, account enumeration, scraping, fake account creation, inventory hoarding, and repeated abuse of promotional or transactional workflows.

Detection can combine request rates with signals such as account behavior, device characteristics, request patterns, and interaction history. Responses can include throttling, additional verification, temporary blocking, or alerts. Using multiple signals is important because attackers can distribute requests across many IP addresses and accounts.

1. Maintain a Complete API Inventory

Maintain an up-to-date inventory of all APIs, including public, partner, internal, and third-party endpoints. Record details such as owners, versions, environments, authentication methods, exposed operations, and the types of data each API processes.

Combine documentation with automated discovery because specifications and asset lists can become outdated. Regularly compare observed API traffic with the approved inventory to identify shadow APIs, undocumented endpoints, and obsolete versions. Retired APIs should be disabled rather than simply removed from documentation.

Key actions:

• Inventory public, partner, internal, and third-party APIs.
• Record owners, versions, environments, authentication methods, and data exposure.
• Use automated discovery to find undocumented and shadow APIs.
• Disable obsolete endpoints and retired API versions.

2. Apply Least-Privilege Access

Grant users, applications, and services only the API permissions required for their tasks. Authorization policies should restrict both the functions an identity can execute and the individual resources it can access.

Use roles, scopes, attributes, or resource ownership rules to make authorization decisions. Avoid broad permissions that apply across an entire API when narrower access is possible. Permissions should also be reviewed as roles and applications change so unnecessary access does not accumulate over time.

Key actions:

• Grant only the permissions required for each task.
• Enforce authorization at both function and resource levels.
• Use roles, scopes, attributes, or ownership rules to restrict access.
• Review permissions regularly and remove unnecessary access.

3. Validate Every API Request

Treat all API input as untrusted, even when requests originate from internal systems or authenticated clients. Validate paths, query parameters, headers, content types, request bodies, data types, allowed values, and payload sizes against clearly defined expectations.

Schema validation can reject malformed requests early, while application-level checks enforce business rules that schemas cannot express. Use parameterized queries and safe parsing methods when passing validated input to databases or other interpreters. Validation should also reject unexpected fields where they could change application behavior.

Key actions:

• Treat requests from both external and internal clients as untrusted.
• Validate parameters, headers, content types, payloads, and allowed values.
• Reject unexpected fields and malformed requests.
• Use parameterized queries and safe parsing methods for accepted input.

4. Rotate and Protect API Credentials

API keys, tokens, certificates, client secrets, and signing keys should be protected throughout their lifecycle. Store secrets in dedicated secret-management systems rather than source code, configuration repositories, client-side applications, or logs.

Use short-lived credentials where possible and establish processes for rotation and revocation. Rotation is particularly important after suspected exposure or personnel and application changes. Monitoring credential use can help detect leaked keys, unexpected locations, or credentials that remain active after they should have been retired.

Key actions:

• Store credentials in dedicated secret-management systems.
• Keep secrets out of source code, client applications, and logs.
• Use short-lived credentials where possible.
• Rotate and revoke credentials when required.
• Monitor for leaked, unexpected, or obsolete credential use.

5. Test APIs Throughout the SDLC

Security testing should begin during API design rather than waiting until production. Review API specifications for unsafe access patterns, test authentication and authorization logic, and use automated testing to identify common implementation flaws during development and continuous integration.

Testing should include cases that normal functional tests may miss, such as changing object identifiers, calling privileged functions with low-privilege accounts, sending unexpected input, and exceeding resource limits. Periodic penetration testing can further evaluate business logic and authorization weaknesses that automated scanners may not detect.

Key actions:

• Review API specifications for security issues during design.
• Test authentication and authorization controls during development.
• Automate API security testing in continuous integration.
• Test object access, privileged functions, unexpected input, and resource limits.
• Use penetration testing to identify business logic and authorization weaknesses.

6. Protect Production APIs Against Runtime Attacks

Predeployment testing cannot identify every vulnerability or prevent abuse of legitimate API functionality. Production APIs therefore need runtime controls such as API gateways, WAAP, rate limiting, bot protection, threat detection, and continuous monitoring.

Runtime protection should establish normal traffic patterns and detect anomalies such as credential attacks, enumeration, unusual request volumes, and access to unexpected endpoints. Security teams should correlate API events with identity and application context, investigate alerts, and update controls as APIs and attack techniques change.

Key actions:

• Deploy API gateways, WAAP, rate limiting, and bot protection.
• Monitor production traffic for abnormal behavior.
• Detect credential attacks, enumeration, and unusual request volumes.
• Correlate API events with identity and application context.
• Investigate alerts and update runtime controls as threats change.

1. Continuous API discovery: Discovers APIs across environments, providing complete visibility into third-party, outdated, shadow, and deprecated APIs, along with the full API catalog to identify trends, anomalies, and application issues.
2. Runtime posture management: Analyzes live production traffic to uncover real risks that traditional tools can't see, helping teams prioritize and manage risk according to actual API runtime behavior.
3. Complete runtime protection: Protects against all types of API attack vectors, including embedded attacks, business logic attacks, and API-focused bot attacks, with coverage of the OWASP API Top 10.
4. Business logic attack mitigation: Automatically maps API workflows, then generates and enforces rules to detect and block sophisticated business logic attacks in runtime.

5. Contextual API testing: Runs fully automated API security testing that adapts to application business logic, integrates into CI/CD pipelines, and helps teams find and fix issues before release.
6. HTTPS DDoS protection for API endpoints: Automatically generates behavior-based signatures in real time to mitigate HTTPS floods on API endpoints without blocking legitimate traffic.
7. AI-based rule automation: Generates and continuously adapts security rules based on runtime production traffic, improving detection accuracy and reducing false positives.
8. Single-portal experience: Combines discovery, management, risk assessment, and runtime protection in one portal, reducing tool sprawl and silos between development and security teams.