What is API Security? Key Threats, Tools & Best Practices

API security is the practice of protecting Application Programming Interfaces from attacks, misuse, and unauthorized access. It focuses on how APIs are built, deployed, and managed to prevent data leaks and system exposure. The goal is to keep APIs functioning safely without risking sensitive information or service integrity.
API-to-API security addresses the protection of interactions between two or more APIs. These exchanges often occur behind the scenes between internal services, making them harder to observe and control. Strong authentication, encrypted communication, and strict access policies are essential to prevent unauthorized data sharing or tampering between connected APIs.
APIs are important for modern software, but without proper security, they expose critical systems and data to serious risks. Here’s why API security matters:
While both aim to protect systems from malicious activity, application security and API security operate at different layers and require distinct approaches. Understanding their differences helps prioritize the right controls and tools based on where the risks lie. Here’s how they compare across key dimensions:
The OWASP API Top 10 is a widely recognized list of the most critical API security threats. Updated in 2023, it helps teams identify common weaknesses in API design and prioritize remediation efforts to reduce risk.
Here are the OWASP top 10 API vulnerabilities as of 2023, in order of severity:
Explore the comparison between OWASP and Pynt API Top 10 Vulnerabilities for 2023. While both lists address common API risks like authorization flaws and misconfigurations, Pynt also identifies emerging threats such as Missing Authentication, Injection, and Local File Access.
While the OWASP API Top 10 highlights critical risks, APIs also face additional threats beyond that list. These issues often target operational gaps, business logic, and evolving technologies.
API vulnerabilities have led to serious data breaches across industries. These incidents highlight how poor authentication, missing access controls, or exposed endpoints can open the door to major compromise.
T-Mobile confirmed in 2023 that a malicious actor exploited one of its APIs to collect personal data from over 37 million customer accounts. The exposed information included names, emails, phone numbers, and billing details. The breach stemmed from an unauthenticated API that allowed access to customer data without proper rate limiting or identity checks.
In 2021, Peloton’s public API was found to expose user account data, including location, gender, and workout metrics, even for profiles marked as private. The API failed to enforce proper authentication or authorization, which allowed anyone to query and retrieve information from millions of user accounts. The issue raised serious concerns about privacy controls and access validation across fitness platforms.
In 2018, Facebook disclosed a vulnerability in its Graph API that allowed attackers to steal access tokens and scrape personal profile data. The issue arose from overly permissive access controls, allowing attackers to pivot from one account to another in their network. Over 50 million users were affected.
Google identified a critical vulnerability in its People API back in 2018 that exposed private profile fields - such as emails, occupations, and gender - to 438 third-party applications. Approximately 500,000 users had their data exposed, even though it was not marked as publicly accessible.
Data classification involves categorizing the data handled by the APIs based on its sensitivity and then applying appropriate security measures based on these categories.
The first step in data classification is to understand what data the APIs handle. This involves analyzing the API's specification and the data it processes. Once the data is understood, it can be categorized into different sensitivity levels, such as public, internal, confidential, or restricted.
Once the data is classified, appropriate security measures can be applied based on its sensitivity. For example, public data may not require any special security measures, while confidential data may require encryption, strict access control, and rigorous auditing.
Implementing robust access control involves ensuring that only authorized users can access the APIs and that they can only perform actions they are permitted to.
Access control can be achieved through various means, such as using OAuth or OpenID Connect for authentication and authorization, implementing Role-Based Access Control (RBAC) or Attribute-Based Access Control (ABAC) to control what actions a user can perform, and using API keys to identify and authenticate API users.
Related content: Read our guide to api exposure
Parameter validation involves checking the data sent to the APIs (the parameters) to ensure they are correct and safe.
Parameter validation can help prevent various API attacks, such as SQL Injection or Cross-Site Scripting (XSS). These attacks involve sending malicious data to the APIs in an attempt to exploit potential vulnerabilities. By validating the parameters, you can ensure they do not contain any harmful data.
Parameter validation should be implemented for all APIs, regardless of their exposure level or functionality. It should also be applied to all types of parameters, whether they are sent in the URL, the query string, the headers, or the body of the API requests. By validating the parameters, you can significantly enhance your API security, preventing potential attacks and maintaining the integrity and reliability of your APIs.
Learn more in our detailed guide to api attacks
Security teams cannot secure what they cannot see. Building an accurate inventory of all API assets is a foundational step in protecting the API landscape. This includes every known and unknown API across environments, covering legacy services, third-party integrations, and internal tools. A reliable inventory helps identify exposed API endpoints, track the full API lifecycle, and align protection strategies with the level of data sensitivity each interface manages. Keeping this catalog current reduces blind spots and supports compliance, testing, and audit efforts.
Continuous visibility into API activity is critical for detecting suspicious behavior. Logging each API call with its associated metadata, including the endpoint accessed, the requesting user, and the time of the call, creates a valuable audit trail. These logs make it easier to uncover signs of API abuse, such as excessive call volumes or unauthorized data access attempts. By centralizing and analyzing these records - often using tools like Postman, Kong, or runtime observability platforms - security teams can improve incident response, reduce dwell time, and reinforce web API security policies in real time.
High-frequency API traffic often signals attack attempts rather than legitimate use. Without rate limiting, malicious actors can overwhelm APIs with automated traffic or flood sensitive endpoints with repeated API calls. Throttling API access according to user roles, origin, and request type adds an important layer of control. This practice helps prevent API abuse, protects resource availability, and supports REST API security standards. Enforcing rate controls also reduces the impact of denial-of-service attacks and narrows the window for credential stuffing campaigns to succeed.
Encrypting the data sent to and from the APIs is an effective way to prevent unauthorized access or tampering. Encryption can be achieved through various means, such as using HTTPS for secure API communication, implementing Transport Layer Security (TLS) to encrypt the data in transit, and using encryption algorithms such as AES or RSA to encrypt the data at rest.
Encrypting API requests and responses not only protects the data from potential eavesdropping or tampering but also helps maintain the privacy and integrity of the data. By encrypting your API communication, you can ensure the security of your data, even if it is intercepted or accessed by unauthorized parties.
Lastly, continuous security is an overarching best practice in API security. It involves continuously monitoring, testing, and improving the API security measures to ensure they remain effective in the face of evolving threats and changing API usage patterns.
Continuous security can be achieved through various means, such as continuously monitoring and analyzing API security events, regularly conducting API security testing to uncover and fix potential vulnerabilities, and integrating automated security tools into CI/CD pipelines to continuously check and enforce the API security measures.
Continuous security requires constant vigilance, regular reviews, and continuous improvement to ensure the APIs remain secure. It can help keep your APIs secure, even as the threat landscape evolves and your APIs grow and change.
Learn more in our detailed guide to API security best practices
Back-end APIs often serve as the core infrastructure for internal services, data pipelines, and microservice communication. While not exposed directly to end users, these APIs still face serious security risks. Misconfigured API endpoints, missing authentication layers, and unchecked API calls can lead to unauthorized access, data leakage, or full system compromise.
Securing them requires deliberate design choices and proactive controls:
Different API architectures come with varying models of security, strengths, and risks. Comparing them side by side helps teams choose the right protocol based on their use case and security requirements.
API security management is the process of protecting APIs from threats, ensuring they function securely while handling sensitive data. It involves implementing security measures to prevent unauthorized access, data breaches, and cyberattacks.
An API gateway helps enforce these security measures, acting as a protective layer between clients and APIs.
There are many tools and solutions available to help organizations enhance their API security. These tools provide functionalities such as vulnerability scanning, threat modeling, and security monitoring, among others.
API security tools can be broadly categorized into two types: static and dynamic:
There are several other important aspects of API security:
Related content: Read our guide to api compliance
Let’s explore the key capabilities of API security solutions in more detail.
One of the most crucial aspects of API security is having an accurate inventory of all your APIs because you can't protect what you don't know. Many organizations have hundreds or even thousands of APIs, making it challenging to keep track of them all. This is where API inventory and discovery tools come into play.
API inventory and discovery tools help you identify all your APIs, both public and private. They provide a centralized view of all your APIs, along with detailed information such as their endpoints, methods, and data types, among others. This not only helps you understand your API landscape better but also enables you to identify potential security risks and take appropriate measures to mitigate them.
These tools also help you keep your API inventory up to date. As your organization grows and evolves, so do your APIs. New APIs are developed, existing ones are modified, and old ones are deprecated. API inventory and discovery tools automatically detect these changes and update your API inventory accordingly.
Pynt performs API inventory and discovery primarily through:
Learn more about Pynt’s API Inventory and Discovery
API posture management involves assessing your APIs' security status and implementing measures to improve it. This involves various activities such as vulnerability scanning, threat modeling, and compliance monitoring, among others.
API posture management tools help you automate these activities. They continuously scan your APIs for vulnerabilities, model potential threats, and monitor your APIs' compliance with various security standards and regulations. This helps you identify and fix security issues before they can be exploited, thereby enhancing your API security.
These tools provide detailed reports and dashboards, giving you a clear view of your APIs' security posture. This allows you to track your APIs' security status over time, understand trends, and make informed decisions to improve your API security.
Related content: Read our guide to api scanning
API runtime protection involves monitoring and controlling API requests and responses in real-time to prevent unauthorized access or data breaches. This layer of security is essential because APIs, by their very nature, expose an application's internal workings to the outside world.
The central aspect of API runtime protection is ensuring that only authorized users have access to the APIs. This is typically achieved through authentication and authorization mechanisms such as OAuth or OpenID Connect. Additionally, protection against API-specific attacks such as SQL Injection, Cross-Site Scripting (XSS), or Denial-of-Service (DoS) is crucial.
Protecting APIs at runtime also involves monitoring and limiting the rate of API requests. This not only prevents potential DoS attacks but also helps maintain the application's performance and stability by preventing overuse or abuse of the APIs.
Unlike traditional security testing methods that focus on the user interface level, API security testing probes deeper into the application, examining the APIs for potential security vulnerabilities.
The first step usually involves understanding the API's structure and functionality. This requires analyzing the API's specification (such as the OpenAPI Specification) and the data it handles.
Once the API's workings are understood, various testing techniques can be employed. These include fuzz testing (sending random, unexpected data to the API to see how it reacts), boundary value analysis (testing the API's response to values at the extremes of what it should accept), and penetration testing (attempting to 'hack' the API to uncover potential vulnerabilities).
Pynt's API security testing incorporates:
Learn more about Pynt’s API Security Testing
API governance is an overarching component of API security. It involves defining and implementing policies, procedures, and standards for API usage and management. This not only helps maintain API security but also ensures the APIs are used effectively and efficiently, delivering maximum value to the organization.
API governance policies typically cover various aspects of API usage, such as authentication and authorization, rate limiting, data privacy, and error handling. Also important is monitoring and enforcing these policies. This can be achieved through various means, such as logging and auditing API usage, implementing API gateways to control and monitor API traffic, and using API management platforms to manage and enforce the API governance policies.
Learn more in our detailed guide to api governance
Pynt's approach to API security emphasizes a 'shift-left' methodology, focusing on early discovery and resolution of vulnerabilities. This proactive stance in the software development life cycle allows for:
These aspects collectively enhance the overall security posture by addressing API vulnerabilities at their inception, rather than as an afterthought.
Related content: Read our guide to API discovery
APIs are at the core of modern digital services, but their expanding complexity demands stronger security measures. Misconfigurations, weak authentication, and unmonitored endpoints can expose systems to serious threats that affect data integrity, service availability, and customer trust.
Organizations can strengthen their API defenses by applying proven security best practices, maintaining a complete and accurate API inventory, and using specialized tools for monitoring, testing, and access control. Securing APIs is not a one-time task but an ongoing effort that must evolve alongside the technologies and threats shaping the software ecosystem. As APIs continue to power AI systems, mobile applications, and cross-platform integrations, protecting them is more than a technical necessity. It is a foundational step toward building lasting digital trust and ensuring resilience in a constantly shifting threat landscape.
API security standards guide how APIs should be secured across their lifecycle, from design to deprecation. Key standards include:
A zombie API is an outdated or deprecated API endpoint that remains publicly accessible despite no longer being maintained or documented. These forgotten interfaces often arise from microservice sprawl or incomplete decommissioning in CI/CD pipelines. Since they typically escape version control and security testing, they become high-risk targets for exploitation.
Securing an API without authentication is only appropriate for low-risk scenarios, such as open data feeds or internal systems that do not handle sensitive information. In these cases, security relies on layered compensating controls. Rate limiting, throttling, and IP filtering can restrict traffic volume and origin, while limiting endpoints to read-only access ensures that no data can be modified. Input validation and schema enforcement help prevent injection and misuse.
Logging every request adds visibility into usage patterns and supports anomaly detection. Finally, using API keys or allow lists—even without full authentication—can help control access in a basic but effective way.
The API security lifecycle involves securing APIs across all phases of development and use:
APIs are protected using TLS (the modern version of SSL) through the following:
API gateways serve as centralized points of enforcement for API traffic. They help secure APIs by:
APIs use encryption to protect data both in transit and at rest:
API security scanning is the process of testing APIs to identify security flaws throughout their lifecycle. It combines early-stage testing during development with continuous monitoring in production environments.
One method focuses on shift-left testing, where simulated attacks are used during the build phase to identify issues such as broken authentication, excessive data exposure, or insecure logic. The other involves real-time scanning of live API traffic to detect threats such as abuse patterns, unauthorized access attempts, or anomalous behavior.
Together, these approaches reduce risk, prevent data leaks, and help ensure APIs remain secure from development through deployment and beyond.
See Additional Guides on Key Application Security Topics
Together with our content partners, we have authored in-depth guides on several other topics that can also be useful as you explore the world of application security.
Authored by Pynt
Authored by Pynt
Authored by Imperva