What is API Security?

Discover the essence of API security: Learn key concepts, best practices, and tools to safeguard your digital assets effectively.

API security, part of Web Application Security, refers to the protection of the integrity, confidentiality, and availability of Application Programming Interfaces (APIs). They allow different software systems to communicate with each other and exchange data, and are a crucial part of modern applications. However, because APIs often provide access to sensitive data and functionality, securing them is of utmost importance.

APIs are essentially a set of rules that define how applications can interact with each other. They provide a standardized way for systems to communicate, and enable developers to more efficiently build complex applications by leveraging the functionality of other software.

However, the very nature of APIs - exposing application logic and sensitive data endpoints - makes them a prime target for attackers. The goal of API security is to address these risks by implementing a multi-layered defense strategy, involving people, processes, and technology.

What Are the Most Common API Security Risks?

The Open Web Application Security Project (OWASP) maintains a “Top 10” list of the main security risks faced by APIs. The latest edition, called “OWASP API Security Top 10 2023”, includes the following:

Broken Object Level Authorization: APIs often expose object IDs, creating a wide attack surface for access control issues.

Broken Authentication: Incorrectly implemented authentication, weak cryptographic algorithms, missing or ineffective multifactor authentication, and other flaws can allow attackers to assume other users’ identities.

Broken Object Property Level Authorization: Lack of proper authorization at the object property level can lead to data exposure or unintended modification.

Unrestricted Resource Consumption: Without restrictions on resource (CPU, memory, storage, or requests to integrated services) consumption, APIs are susceptible to Denial of Service (DoS) attacks.

Broken Function Level Authorization: Complex access control policies with different roles and groups can lead to authorization flaws if not properly implemented.

Unrestricted Access to Sensitive Business Flows: APIs that expose sensitive business flows, like purchasing or posting comments, without compensating controls are vulnerable to abuse. Attackers can exploit these to perform actions at a scale and speed not possible through the UI, causing business harm.

Server Side Request Forgery (SSRF): These flaws allow an attacker to induce the API server to make HTTP requests to an arbitrary domain. They can be used to bypass firewalls, access unreachable services, or perform port scanning to disclose sensitive information.

Security Misconfiguration: Insecure default configurations, misconfigured HTTP headers, unnecessary HTTP methods, permissive Cross-Origin Resource Sharing (CORS), and verbose error messages containing sensitive information can expose APIs to attack.

Improper Inventory Management: With larger and more complex APIs, it’s easy to lose track of exposed API endpoints, versions, and which clients/apps are accessing them. Lack of visibility makes it harder to detect and fix vulnerabilities.

Unsafe Consumption of APIs: Vulnerabilities or misconfigurations in third-party APIs or web services used by the API can introduce vulnerabilities in your applications. Excessive data exposure, SSRF, SQL injection, and other flaws can result from unsafe consumption without proper user input validation and security controls.

What Are the API Security Best Practices?

API security best practices are a set of guidelines and techniques that organizations should follow to protect their APIs from unauthorized access, misuse, and attacks. By adhering to these and continuously reviewing and improving their API security posture, organizations can ensure the confidentiality, integrity, and availability of their APIs and the data they handle. They include:

Design APIs with security in mind from the start: integrate security into every phase of the API lifecycle, from design and development to testing and deployment. Follow secure coding practices, use security frameworks and libraries, and conduct regular code reviews to catch vulnerabilities early.

Use strong authentication protocols like OAuth 2.0: implement OAuth 2.0 for authentication to securely manage API access tokens. Use strong cryptographic algorithms for token signing, validation and expiration enforcement on the server side.

Implement proper authorization at object and function level: ensure every API endpoint authorizes requests based on the user’s permissions. Use role-based or attribute-based access control to enforce fine-grained permissions at the object and function level. Regularly audit and test authorization controls.

Encrypt sensitive data in transit and at rest with TLS: use HTTPS/TLS for all API communications to encrypt data in transit. Verify server certificates and use strong cipher suites. Encrypt sensitive data stored in databases or files using strong encryption algorithms and manage keys securely.

Validate and sanitize all API inputs: treat all client-supplied data as untrusted and validate it thoroughly. Sanitize inputs to prevent injection attacks, enforce schema validation, and use type-safe parameterized queries. Implement input validation on the server side, not just in client applications.

Use API gateways to manage and monitor API traffic: deploy API gateways to centrally manage and monitor API traffic. Use gateways to enforce authentication, rate limiting, and other security policies. Monitor API usage and performance to detect anomalies and potential attacks.

Enforce rate limiting to prevent abuse and DoS attacks: implement rate limiting to restrict the number of API requests a client can make in a given time period. This prevents abuse, protects against DoS attacks, and helps maintain API availability. Use techniques like throttling and spike arrest.

Maintain an up-to-date inventory of all APIs: keep a complete inventory of all APIs, including versions, endpoints, and access permissions. Use API management tools to automate discovery and documentation. Regularly review the inventory to identify deprecated or unused APIs that should be removed.

Regularly audit APIs and remediate vulnerabilities: conduct regular security audits and penetration tests to identify vulnerabilities in APIs and their underlying infrastructure. Prioritize and remediate found vulnerabilities based on risk severity. Continuously monitor for new threats and vulnerabilities.

Monitor API activity for anomalies and potential threats: implement real-time monitoring and logging of API activity. Use security information and event management (SIEM) tools to correlate and analyze logs for anomalies and potential threats. Set up alerts for high-risk events and suspicious behavior.

Have an incident response plan for API security breaches: develop and regularly test an incident response plan specific to API security breaches. Define roles and responsibilities, communication channels, and containment and recovery procedures. Conduct post-incident reviews to identify root causes and improvement areas.

What Is the Relation Between API Security and Mobile App Security?

API security has a significant impact on mobile app security because mobile apps rely heavily on APIs to function. Most mobile apps interface with multiple backend APIs to access data, enable features, and power the app’s functionality.

This means the security of the mobile app is directly tied to the security of the APIs it uses. If an API has vulnerabilities or is misconfigured, it can jeopardize the security of the mobile app and the sensitive data it handles.

APIs expand the attack surface of mobile apps because each API a mobile app uses represents a potential entry point for attackers. The decentralized nature of mobile apps and their reliance on client-side processing amplifies this risk. Attackers can exploit vulnerabilities in APIs to gain unauthorized access to data, perform malicious actions, and disrupt service.

Many high-profile mobile app security breaches in recent years resulted from API vulnerabilities. The Parler social media app data breach in 2021 occurred because of a weak API that allowed scraping of user data. This highlights the real-world impact of API security on mobile apps.

How to Implement an API Security Strategy?

Implementing a comprehensive security modernization strategy requires a holistic approach involving people, processes, and technology. It should be an ongoing program integrated into the entire API lifecycle, not a one-time project.

The foundation of an effective strategy is establishing clear API security policies and standards based on industry best practices and compliance requirements. These policies guide all aspects of API security. Equally important is educating and training all stakeholders - developers, testers, operations, and business users - on API security risks and their roles in mitigating them.

Integrating security measures into the API development lifecycle is crucial. Security requirements should be defined early and continuously validated through automated testing. Robust processes are needed for auditing APIs, managing credentials, and handling incidents.

Leveraging secure coding practices, data encryption, strong authentication and authorization, API gateways, and real-time monitoring solutions is key to protecting APIs. Continuous review and improvement are essential as APIs and threats evolve.

API Security Tools and Technologies

API gateways and management platforms play a crucial role in securing APIs. These tools act as a central point of control, enabling organizations to enforce security policies, manage traffic, and monitor API usage. By routing API requests through a gateway, companies can apply authentication, authorization, and rate limiting consistently across all APIs.

Web Application Firewalls (WAFs) are a key technology for protecting APIs. While traditionally used for securing web applications, some WAFs have evolved into WAAP (Web Application and API Protection) solutions capable to understand and inspect API traffic. They can detect and block common API attacks like SQL injection, cross-site scripting (XSS), and XML external entities (XXE) by analyzing API requests and responses for malicious patterns.

Authentication and authorization frameworks are foundational for API security. Standards like OAuth 2.0 and OpenID Connect provide secure mechanisms for granting API access and validating client identities. JSON Web Tokens (JWTs) are often used in conjunction with these frameworks to securely transmit authentication information in API requests.

Encryption and digital signature solutions are essential for protecting sensitive data transmitted via APIs. Transport Layer Security (TLS) encrypts API traffic in transit, preventing eavesdropping and tampering. JSON Web Encryption (JWE) and JSON Web Signature (JWS) can be used to encrypt and sign API payloads, ensuring confidentiality and integrity of sensitive data.

Security testing and vulnerability scanning tools are indispensable for identifying weaknesses in APIs before they can be exploited. Dynamic application security testing (DAST) tools can automatically probe APIs for common vulnerabilities, while static application security testing (SAST) analyzes API code for security flaws. Regular penetration testing and bug bounty programs can further strengthen API security posture.

By leveraging these various tools and technologies in a layered approach, organizations can significantly enhance the security of their APIs.


As APIs become increasingly critical to business, securing them properly is essential. By understanding the common API security risks and implementing best practices, organizations can protect their APIs from abuse and attack. Remember: API security is an ongoing process that requires constant vigilance and adaptation as the API landscape continues to evolve.

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