# API Security: Common Risks and How to Prevent Them Modern applications heavily rely on APIs. They allow applications, services and systems to communicate with each other. They are used within websites, mobile applications, payment platforms, cloud services and many other technologies. For example, a mobile application may make an API call to retrieve the users profile information. However, they often contain sensitive information and important functions, so if not secured properly can allow exposure of data or users doing things they shouldn’t be able to do. Therefore, **API Security** is an important part of developing modern applications. In this article, we will look at some common API security issues, why they are important and how developers can reduce the risk. ## 1. What is API Security? API Security is the set of practices, technologies and policies that are used to secure APIs. This ensures: - Only authorised users and applications can access secure endpoints. - Users can only access the information they should be able to. - Sensitive data is kept safe during transfer. - Requests to the API are validated. - Unusual or excessive activity can be spotted. - APIs are configured securely. API security should be considered during development. ## 2. Why is API Security Important? APIs often provide a link between users, applications and backend services. This means if there is a security issue with your API it can cause issues across different areas of your application. Some common issues include: - **Sensitive Data Exposure** – The API may return data that shouldn’t be available to the user. - **Broken Authentication** – Poor authentication can allow unauthorised users to gain access to accounts. - **Broken Authorisation** – Users can access resources for other users. - **Excessive Requests** – Poor resource management can cause issues with availability of the application. - **Security Misconfiguration** – Misconfigured settings can expose services or sensitive data. - **Third Party** – The application may be using third party APIs. The OWASP API Security Top 10 provides a good reference. ## 3. Common API Security Issues ### 3.1 Broken Object Level Authorization (BOLA) This occurs when the API doesn’t validate if the user has access to a specific object. For example, an application may allow users to view their profile using an endpoint which requires a user ID. However, if the backend only checks if the user is logged in and doesn’t check if they are the owner of the profile, this could expose information. How to prevent: - Validate if the user owns the resource on the server side. - Ensure all requests for secured objects are checked for permissions. - Never trust client side IDs. - Include authorisation checks during development. Authentication is used to verify who a user or application is. Poor authentication can leave your API vulnerable to account compromise. Common issues include: - Poor password policies. - Poor token management. - No Multi-Factor Authentication for sensitive accounts. - Incorrect session management. - Tokens are valid for too long. How to prevent: - Use standard authentication methods. - Secure your authentication tokens. - Ensure tokens expire after a certain time. - Secure session management. - Use Multi-Factor Authentication. ### 3.3 Broken Object Property Level Authorization This occurs when an API returns or allows changes to properties for an object without checking if the user has permission. For example, a profile endpoint may return internal account information which should only be seen by admins. How to prevent: - Only return the fields required. - Validate the properties users can change. - Add permissions to properties. - Don’t automatically return whole objects from the database. ### 3.4 Unrestricted Resource Consumption APIs use resources such as CPU, Memory, Storage and Bandwidth. If you don’t restrict how much resources are being used, you can have excessive requests which may impact availability. How to prevent: - Rate limit. - Limit how much data can be sent in a request. - Pagination. - Set appropriate timeouts. - Monitor resource usage. ### 3.5 Broken Function Level Authorization This occurs when users can access functions that should be restricted to other roles. For example, a standard user shouldn’t automatically have access to admin functions. How to prevent: - Enforce permissions on the server. - Implement Role Based Access Control. - Check authorisation for sensitive functions. - Test different user roles have the correct access. ### 3.6 Security Misconfiguration Misconfigured APIs can cause unnecessary security risks. Examples include: - Debug information being exposed in production. - Unnecessary endpoints enabled. - Incorrect CORS configuration. - No security headers. - Too many permissions. How to prevent: - Check configurations in production. - Disable any unnecessary services. - Keep dependencies up to date. - Don’t expose internal error details. - Regularly check API security settings. ## 4. Authentication vs Authorisation Authentication and authorisation are closely related but serve different purposes. **Authentication** - Verifies Identity Example: Who are you? - Often uses passwords, tokens or MFA - Happens before protected access is granted **Authorisation** - Determines Permissions Example: What can you access? - User roles, policies, and permissions - Determines which actions are allowed For example, a user may successfully authenticate to an application but still be denied access to an administrator endpoint. This is why both authentication and authorisation are necessary. ## 5. Best Practice As a developer you can implement the following to improve API security: - **Use HTTPS:** Protect data while it travels between clients and servers. - **Validate input:** Check incoming data before processing it. - **Enforce authorisation:** Verify permissions for every protected operation. - **Use secure authentication:** Follow established authentication standards. - **Apply rate limiting:** Reduce excessive or abusive requests. - **Protect sensitive information:** Avoid returning unnecessary personal or internal data. - **Manage API keys securely:** Do not expose secrets in public repositories or frontend code. - **Maintain an API inventory:** Know which endpoints and versions are active. - **Monitor API activity:** Record relevant security events. - **Update dependencies:** Address known vulnerabilities in libraries and frameworks. ## 6. Testing Testing should be done during development. Testing can include: - Authentication. - Authorisation. - Validation. - Rate limiting. - Error handling. - Dependencies and configurations. - Different user roles. As a developer you should also check the documentation for your API to make sure it is accurate. Only test in systems you have permission to. ## 7. OWASP The Open Worldwide Application Security Project publish guidelines to help developers understand security risks within their applications. The OWASP API Security Top 10:2023 lists 10 important security issues for APIs: - Broken Object Level Authorization. - Broken Authentication. - Broken Object Property Level Authorization. - Unrestricted Resource Consumption. - Broken Function Level Authorization. - Unrestricted Access to Sensitive Business Flows. - Server Side Request Forgery. - Security Misconfiguration. - Improper Inventory Management. - Unsafe Consumption of APIs. This is a good starting point for developers looking to improve their API security. This isn’t an exhaustive list of all vulnerabilities. ## 8. Future of API Security APIs will continue to be an important part of applications. With the rise of microservices, cloud platforms, mobile applications and third party integrations, it is important to ensure you have secure communication between services. Developers will need to focus on: - Strong identity and access management. - Automated security testing. - Inventory management. - Secure communication between services. - Monitoring and anomaly detection. - Securing sensitive business functions. API security will continue to be an important responsibility for developers and security professionals. ## Conclusion APIs are an essential part of modern software, but can introduce security risks. Poor authentication, broken authorisation, excessive resource usage and security misconfiguration can expose your application and sensitive data. By following best practice and using resources like the OWASP API Security Top 10 you can create more secure and reliable APIs. API security should never be an optional feature, it should be considered at all stages of application development. ## References [OWASP API Security Project](https://owasp.org/www-project-api-security/) [OWASP API Security Top 10](https://owasp.org/API-Security/) [OWASP REST Security Cheat Sheet](https://cheatsheetseries.owasp.org/cheatsheets/REST_Security_Cheat_Sheet.html)