Last Updated on May 15, 2026 by Arnav Sharma

OWASP API Security Top 10: Complete Guide for 2024

The OWASP API Security Top 10 represents the most critical security risks facing APIs in modern applications. As APIs become the backbone of digital infrastructure across Australian organisations, understanding these vulnerabilities is essential for security architects and DevOps teams. This comprehensive guide examines each vulnerability with practical prevention strategies and real-world examples from the field.

According to the 2023 State of API Security Report by Salt Security, API attacks increased by 117% year-over-year, with 94% of organisations experiencing API security incidents. For Australian practitioners working under ACSC guidelines and Essential Eight requirements, API security has become a critical compliance and operational concern.

Understanding the OWASP API Security Framework

The OWASP API Security Top 10 emerged from extensive analysis of real-world API vulnerabilities reported by security researchers, penetration testers, and incident response teams globally. Unlike generic security checklists, this framework reflects actual attack patterns observed in production environments.

The current API Security Top 10 includes:

• API1:2023 Broken Object Level Authorization
• API2:2023 Broken Authentication
• API3:2023 Broken Object Property Level Authorization
• API4:2023 Unrestricted Resource Consumption
• API5:2023 Broken Function Level Authorization
• API6:2023 Unrestricted Access to Sensitive Business Flows
• API7:2023 Server Side Request Forgery
• API8:2023 Security Misconfiguration
• API9:2023 Improper Inventory Management
• API10:2023 Unsafe Consumption of APIs

For Australian organisations, these vulnerabilities pose particular risks given the Notifiable Data Breaches (NDB) scheme requirements and increasing regulatory scrutiny under the Privacy Act amendments.

API1: Broken Object Level Authorization

Broken Object Level Authorization occurs when APIs fail to verify that authenticated users should access specific objects they request. This vulnerability consistently ranks first due to its prevalence and severe impact on data confidentiality.

A typical attack scenario involves modifying object identifiers in API requests. For example, an authenticated user accesses /api/accounts/12345 but changes the ID to 12346 to access another user’s account data. The API validates authentication but skips object-level authorization checks.

During a 2023 security assessment of a major Australian financial services API, researchers discovered that 78% of endpoints with object references lacked proper authorization controls, potentially exposing customer financial data across multiple accounts.

Prevention Strategies:

• Implement authorization checks for every object access, not just endpoint access
• Use indirect object references instead of exposing database IDs
• Validate user permissions against requested resources using access control matrices
• Implement role-based access controls tied to specific data ownership
• Log all object access attempts for security monitoring

API2: Broken Authentication

Broken Authentication encompasses various authentication mechanism failures that allow attackers to compromise user accounts or assume other users’ identities. This includes weak password policies, predictable session management, and bypassable authentication logic.

Common manifestations include APIs accepting default credentials, session tokens following predictable patterns, or authentication flows that can be circumvented through parameter manipulation. The 2022 LastPass breach demonstrated how authentication weaknesses in APIs can lead to widespread credential compromise.

Australian organisations face particular challenges here due to the government’s Strong Customer Authentication requirements for financial services and the ACSC’s authentication guidelines for government systems.

Implementation Requirements:

• Enforce multi-factor authentication for sensitive operations
• Generate cryptographically secure, unpredictable session tokens
• Implement account lockout mechanisms after failed attempts
• Use proper password hashing algorithms (bcrypt, Argon2)
• Set appropriate session timeouts and secure logout procedures

API3: Broken Object Property Level Authorization

This vulnerability combines aspects of excessive data exposure and mass assignment, occurring when APIs fail to control which object properties users can read or modify. It represents a more granular authorization failure than traditional object-level issues.

Consider a user profile API where authenticated users should modify their name and email but not their account balance or administrative privileges. Broken property-level authorization might allow users to read sensitive properties in API responses or modify restricted fields through API requests.

A recent penetration test of an Australian e-commerce platform revealed that customer APIs returned internal pricing tiers and supplier information alongside standard product data, exposing commercially sensitive information to competitors.

Control Mechanisms:

• Implement field-level permissions controlling readable and writable properties
• Use data transfer objects (DTOs) to explicitly define allowed properties
• Validate all input properties against allow-lists
• Apply different property access rules based on user roles
• Monitor for unexpected property access patterns

API4: Unrestricted Resource Consumption

Unrestricted Resource Consumption replaces the previous “Lack of Resources and Rate Limiting” category, encompassing broader resource abuse scenarios. This includes traditional denial-of-service attacks, resource exhaustion through expensive operations, and business logic abuse.

Modern attacks target APIs through automated scraping, credential stuffing campaigns, and resource-intensive operations like file uploads or database queries. Without proper controls, attackers can overwhelm infrastructure or generate excessive costs in cloud environments.

Australian government agencies must consider this vulnerability carefully under the ACSC’s Guidelines for System Monitoring, particularly for citizen-facing services that must remain available during high-demand periods.

Resource Type	Attack Vector	Mitigation Approach
Network Bandwidth	Large payload flooding	Request size limits, payload validation
CPU Processing	Complex query operations	Query complexity analysis, timeouts
Memory Usage	Large response sets	Pagination, response caching
Storage Space	Unlimited file uploads	File size limits, quota management

API5: Broken Function Level Authorization

Function Level Authorization failures occur when APIs don’t properly verify whether users should access specific functions or endpoints. This differs from object-level authorization by focusing on operational permissions rather than data access rights.

Administrative functions represent prime targets for this vulnerability. Attackers might discover endpoints like /api/admin/users/delete or /api/reports/financial and attempt access without proper authorization checks server-side.

During a 2023 security review of Australian university student information systems, researchers found that 34% of administrative API functions relied solely on client-side access controls, allowing privilege escalation through direct API calls.

Authorization Architecture:

• Implement role-based access control (RBAC) consistently across all endpoints
• Validate permissions server-side for every function call
• Apply principle of least privilege for function access
• Document and regularly audit function-level permissions
• Implement centralized authorization services for complex applications

API6: Unrestricted Access to Sensitive Business Flows

This new category addresses automated abuse of legitimate business functionality. Unlike traditional DoS attacks, these attacks use normal API functions in ways that harm business operations or violate business logic.

Examples include automated ticket purchasing for resale, bulk account creation for spam, or rapid property inquiry submissions to gather market intelligence. These attacks often appear legitimate individually but cause harm at scale.

Australian retail APIs frequently encounter this during product launches or sales events, where automated systems overwhelm genuine customer access. The competition and consumer protection implications make this particularly relevant for ACCC compliance considerations.

Business Flow Protection:

• Implement business logic rate limiting beyond technical rate limits
• Use behavioral analysis to identify automated vs. human usage patterns
• Apply progressive challenges for suspicious activity (CAPTCHA, phone verification)
• Monitor business metrics alongside technical metrics
• Implement fraud detection algorithms for high-risk business flows

API7: Server Side Request Forgery (SSRF)

Server Side Request Forgery vulnerabilities allow attackers to manipulate APIs into making requests to unintended destinations. This can expose internal infrastructure, bypass network segmentation, or access cloud metadata services.

SSRF attacks often target cloud metadata endpoints like http://169.254.169.254/ to extract AWS credentials or instance information. In containerized environments, attackers might access Docker sockets or Kubernetes API servers through SSRF vulnerabilities.

For Australian organisations using Azure services, SSRF vulnerabilities pose particular risks to managed identity tokens and Key Vault access, potentially compromising entire cloud environments.

SSRF Prevention Measures:

• Validate and sanitize all user-supplied URLs
• Implement allow-lists for permitted destinations
• Use network segmentation to isolate API infrastructure
• Disable unnecessary HTTP methods and URL schemes
• Monitor outbound requests for suspicious patterns

API8: Security Misconfiguration

Security Misconfiguration encompasses various configuration failures that expose APIs to attack. This includes default credentials, unnecessary HTTP methods, verbose error messages, and missing security headers.

Common misconfigurations include leaving debug modes enabled in production, using default API keys, or failing to implement proper CORS policies. The Optus data breach in 2022 highlighted how configuration weaknesses can lead to massive data exposure.

Australian organisations must address security configuration as part of Essential Eight implementation, particularly regarding application hardening and system patching requirements.

Configuration Security Checklist:

• Remove or disable unused API endpoints and HTTP methods
• Implement security headers (HSTS, CSP, X-Frame-Options)
• Configure proper CORS policies for cross-origin requests
• Disable debug modes and verbose error messages in production
• Use configuration management tools to ensure consistent security settings
• Regular security configuration audits and vulnerability scanning

API9: Improper Inventory Management

Improper Inventory Management refers to insufficient visibility and control over API assets. Organizations often lose track of API versions, endpoints, and their security status, creating blind spots for attackers to exploit.

This includes outdated API versions running alongside current ones, undocumented APIs deployed by development teams, and APIs accessing sensitive data without proper oversight. The complexity of microservices architectures exacerbates this challenge.

A 2023 survey of Australian enterprise organizations found that 67% couldn’t accurately enumerate all their public-facing APIs, with many discovering previously unknown endpoints during security assessments.

API Inventory Best Practices:

• Maintain automated API discovery and inventory tools
• Implement API lifecycle management with proper deprecation processes
• Use API gateways to centralize API management and monitoring
• Regular security scanning of all API endpoints
• Document API ownership and responsibility for security updates

API10: Unsafe Consumption of APIs

Unsafe Consumption of APIs occurs when applications trust third-party APIs without proper validation or security controls. This includes consuming malicious data from compromised APIs or failing to validate responses from external services.

Modern applications frequently integrate multiple APIs, creating dependency chains where compromise of one API can impact others. Supply chain attacks increasingly target API integrations to access downstream systems.

Australian government agencies must consider this carefully when integrating with third-party services, particularly under the Protective Security Policy Framework (PSPF) requirements for information and communications technology security.

Secure API Consumption:

• Validate and sanitize all data received from external APIs
• Implement proper error handling for API failures
• Use mutual TLS authentication for sensitive API integrations
• Monitor third-party API security posture and incident notifications
• Implement fallback mechanisms for critical API dependencies

Implementation Strategy for Australian Organizations

Addressing the OWASP API Security Top 10 requires systematic implementation across development lifecycles. Australian organisations should integrate these controls with existing security frameworks and compliance requirements.

Start with automated security testing in CI/CD pipelines, implement API gateways for centralized security controls, and establish regular security assessments. The ACSC’s Information Security Manual provides additional guidance for government organisations implementing API security controls.

Success requires collaboration between security teams, developers, and operations staff. Regular training on API security principles and threat modeling exercises help teams identify vulnerabilities early in development cycles.

By systematically addressing each OWASP API Security Top 10 vulnerability, Australian organizations can significantly improve their API security posture and protect against the evolving threat landscape targeting API infrastructure.