API Security

OWASP Top 10 API Security Risks & Mitigations


In the ever-evolving landscape of cybersecurity, APIs (Application Programming Interface)s have become a fundamental component of modern applications, facilitating seamless communication between different software systems. However, with great power comes great responsibility, and as APIs become more prevalent, the risk of security vulnerabilities increases. The OWASP identifies and ranks the top 10 API security vulnerabilities that organizations should be aware of and address to fortify their systems against potential threats.

1. Broken Object Level Authorization

With this issue attackers exploit API endpoints that are vulnerable by manipulating the ID of an object (object being some kind of resource in your app - this could be representation of a user’s record in a database, for example), leading to unauthorized access to sensitive data. Such attacks are common and give access to other users’ objects which could lead to full account takeover.

Mitigation Strategies:

  • Implement fine-grained access controls to ensure users can only access objects they are authorized to access. Use role-based access control (RBAC) or attribute-based access control (ABAC) mechanisms.
  • Use randomly generated IDs to prevent attackers from guessing object IDs.
  • Validate and sanitize user inputs, especially object IDs, to prevent injection attacks or unauthorized object manipulation.

2. Broken Authentication

This is an issue where misconfigured authentication mechanisms are exploited which can allow attackers to compromise authentication tokens or impersonate other users, resulting in potential data breaches and identity theft.

Mitigation Strategies:

  • Implement well-established and secure authentication methods, such as OAuth 2.0, OpenID Connect, or SAML, based on the specific requirements of your application.
  • Ensure that API tokens and secrets are securely stored in a secure system like Secret Manager or KMS and not exposed in client-side code or public repositories.
  • Avoid exposing whether a user account exists through error messages. Always use generic error messages for login failures.
  • Implement rate limiting and account lockout mechanisms to prevent brute force attacks on user accounts. Limit the number of login attempts allowed within a certain time period and temporarily lock user accounts after multiple failed attempts.

Best Practices:

  • Enforce strong password policies, including requirements for length, complexity, and regular password changes. Encourage the use of password managers and multi-factor authentication (MFA) where possible.

3. Broken Object Property Level Authorization

Broken Object Property Level Authorization combines the vulnerabilities addressed in Excessive Data Exposure and Mass Assignment from the 2019 report[1] and focuses instead on the lack of or improper authorization validation at the object property level (think of a user’s email address on a "user" object). This vulnerability can lead to unauthorized parties gaining access to sensitive information or manipulating data.

Mitigation Strategies:

  • Ensure that users have access to only the object properties they should access.
  • Limit exposure of sensitive properties by only exposing necessary information to authorized users.
  • Validate user input and enforce strict data validation to prevent unauthorized modification of object properties.
  • Encrypt sensitive properties at rest and during transit to protect against unauthorized access and data breaches.

4. Unrestricted Resource Consumption

This risk identifies APIs that do not limit client interactions or resource consumption behind the scenes. Exploitation of this vulnerability can lead to DoS due to resource starvation and increased operational costs (e.g., higher CPU demand, increased cloud storage needs). In today’s Cloud-based pay-as-you-go model, this issue can cripple businesses by pushing operational expenditure through the roof.

Mitigation Strategies:

  • Implement rate limiting based on business needs to control how often clients can interact with the API within defined timeframes.
  • Implement throttling mechanisms to control the rate of API requests based on predefined thresholds, ensuring that resources are allocated fairly among users.
  • Set resource quotas to limit the maximum number of resources (such as memory, CPU, or storage) that a single API request can consume, preventing resource exhaustion attacks.

5. Broken Function Level Authorization

Exploitation of this risk involves sending legitimate API calls to endpoints that should not be accessible and allow attackers unauthorized access to important functionality which may lead to data disclosure, data loss, or data corruption.

Mitigation Strategies:

  • Deny access by default to all resources and require explicit grants to specific roles.
  • Implement authorization checks for administrative functions inside regular controllers.
  • Implement granular access controls at the function level to restrict access to specific functions based on user roles, privileges, or attributes.

6. Unrestricted Access to Sensitive Business Flow

This is where attackers manually identify what resources (e.g. endpoints) are involved in the workflow of a targeted API and how they work together so that they can bypass important steps. Exploitation of this vulnerability may not always have a direct technical impact but can harm the business in various ways, such as preventing legitimate users from purchasing products or causing economic inflation within a system (e.g., a game’s virtual economy).

Mitigation Strategies:

  • Follow the principle of least privilege, granting users only the permissions they need to perform their specific roles and responsibilities. Avoid granting excessive privileges that could result in unauthorized access to sensitive business flows.
  • Implement protection mechanisms to mitigate business risks, such as rate limiting, device fingerprinting, and human detection. These measures help maintain the integrity of sensitive business flows and prevent exploitation by malicious actors.

7. Server-Side Request Forgery (SSRF)

Modern concepts in software development encourage developers to make secondary requests to third party URLs provided by the user. Without proper validation of those URLs, an attacker can manipulate the application and make it act as a proxy for some other malicious activity. This can cause significant financial losses, operational disruptions, data exposure, and reputation damage.

Mitigation Strategies:

  • Isolate the resource fetching mechanism in your network: usually these features are aimed to retrieve remote resources and not internal ones.
  • Whenever possible, use allow lists of:
    • Remote origins users are expected to download resources from (e.g. Google Drive, Gravatar etc.)
    • URL schemes and ports
    • Accepted media types for a given functionality
  • Disable HTTP redirections.
  • Use a well-tested and maintained URL parser to avoid issues caused by URL parsing inconsistencies.

8. Security Misconfiguration

Misconfiguration can happen in all sorts of places from the network layer to the application layer. They can lead to unauthorized access, data exposure, server compromise, repetitional damage, financial losses, and operational disruptions. Preventive measures include encryption, HTTP verb control, CORS policies, security headers, and consistent request processing.

Mitigation Strategies:

  • Ensure that all API communications from the client to the API server and any downstream/upstream components happen over an encrypted communication channel (TLS), regardless of whether it is an internal or public-facing API.
  • Be specific about which HTTP verbs each API can be accessed by all other HTTP verbs should be disabled (e.g. HEAD).
  • APIs expecting to be accessed from browser-based clients (e.g. WebApp front-end) should, at least:
    • Implement a proper Cross-Origin Resource Sharing (CORS) policy
    • Include applicable Security Headers
  • Restrict incoming content types/data formats to those that meet the business/ functional requirement.

9. Improper Inventory Management

Outdated documentation complicates the process of identifying and addressing vulnerabilities, while the absence of asset inventory and retirement strategies leads to the operation of unpatched systems, resulting in the exposure of sensitive data.

Mitigation Strategies:

  • Maintain an up-to-date inventory of all API versions, including those in development, testing, and production environments. Ensure that all versions are properly documented and tracked.
  • Implement version control systems (e.g. Git) to manage changes to APIs effectively. Use branching and tagging mechanisms to organize and track different versions and enforce code review processes to ensure changes are properly reviewed and approved before deployment.
  • Define clear policies and procedures for the lifecycle management of APIs, including versioning, deprecation, and retirement. Regularly review and update API documentation to reflect changes in versioning and ensure consistency across all environments.
  • Implement access controls to restrict access to non-production API versions. Limit access to development and testing environments to authorized personnel only and enforce authentication and authorization mechanisms to prevent unauthorized access.

10. Unsafe Consumption of APIs

This risk describes how developers trust data received from third-party APIs more than user input, especially if those APIs are offered by well-known companies. This can lead to weaker security practices which allow attackers to identify and potentially compromise other integrated APIs or services, often not publicly disclosed or easily exploitable. The impact varies based on how the target API handles the data, potentially resulting in unauthorized data exposure, various types of injections, or denial of service.

Mitigation Strategies:

  • Evaluate the security posture of service providers before integrating their APIs.
  • Ensure that all API interactions occur over a secure communication channel (TLS).
  • Always validate and properly sanitize data received from integrated APIs before using it.
  • Maintain an allowlist of well-known locations that integrated APIs may redirect to and avoid blindly following redirects to untrusted sources.


Understanding and addressing these OWASP Top 10 API security vulnerabilities is paramount for organizations looking to secure their systems against potential threats.

By implementing robust authentication mechanisms, access controls, and regular security audits, businesses can ensure the integrity, confidentiality, and availability of their APIs, ultimately safeguarding their valuable data and maintaining the trust of users and stakeholders.


1. OWASP API Security Project

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