What Is REST API Security?

REST APIs are widely used today, but their popularity makes them prime targets for cyberattacks. Securing REST APIs is essential to protect sensitive information and ensure the reliability of web applications. This guide explores various security measures, including encryption, access control, rate limiting, and API monitoring, to help secure REST APIs and mitigate vulnerabilities.

For a variety of reasons, securing REST APIs is a critical undertaking for enterprise cybersecurity practitioners. Because APIs expose applications and sensitive data to external access, they are a favorite target of malicious actors that cause data breaches. Naturally, organizations must invest in API security tools to protect their REST APIs. API security comprises a range of countermeasures that include encryption, rate limiting, access tokens, and more. We’ll explore these security controls and how they can enhance your REST API security.

The REST architectural style was defined in Dr. Roy Fielding’s dissertation published in 2000. The goal of this paper was to define a uniform and consistent architectural approach for machine-to-machine communication on the web. A REST API is an API that uses the REST (REpresentational State Transfer) architectural style to send and receive data and procedure calls. A REST API also needs a transport protocol and a programming language to function. REST APIs communicate over Hypertext Transfer Protocol (HTTP), and the preferred data format for messages transmitted is JavaScript Object Notation (JSON). Thus, the term “API” almost always refers to a REST API that uses JSON over HTTP.

The REST API became the predominant mode for APIs for several reasons. For one thing, it is free and standards-based, so there are almost no barriers to its adoption. RESTful programming is also “stateless,” which makes it easy to manage. A RESTful interface is uniform. Query parameters are standardized. As a result, it is quite easy for an entity that creates an API to publish instructions for developers to use when invoking the API, e.g., Here’s how to get data from the API, which will be returned in JSON. Other types of responses are possible, too, including Extensible Markup Language (XML), documents, and images.

Without proper safeguards, REST APIs represent an extensive, vulnerable attack surface. While organizations could previously rely on “security through obscurity,” wherein hackers would have to work hard to find data inside a network with an API, the organization literally publishes instructions on how to find the data and steal it.

REST API security practices have matured. The most effective countermeasures include:

It’s not uncommon to have APIs that no one knows about. Most organizations have little to no visibility into a large percentage of their API traffic, often because they assume all of their APIs are routed through an API gateway. But that is not the case. Your enterprise is exposed to a range of risks without a complete and accurate inventory. Core capabilities needed:

• Locating and inventorying all of your APIs, regardless of configuration or type
• Detecting dormant, legacy, and zombie APIs
• Identifying forgotten, neglected, or otherwise unknown shadow domains
• Eliminating blind spots and uncovering potential attack paths

With a complete API inventory in place, it’s critical to understand what types of data flow through your APIs and how that affects your ability to comply with regulatory requirements. API posture management provides a comprehensive view of traffic, code, and configurations to assess your organization’s API security posture. Core capabilities needed:

• Automatically scanning infrastructure to uncover misconfigurations and hidden risks
• Creating custom workflows to notify key stakeholders of vulnerabilities
• Identifying which APIs and internal users are able to access sensitive data
• Assigning severity rankings to detected issues to prioritize remediation

You’re no doubt familiar with the concept of “assume breach.” API-specific breaches and attacks are reaching that same degree of inevitability. For all of your APIs that are live in production, you need to be able to detect and block attacks in real time. Core capabilities needed:

• Monitoring for data tampering and leakage, policy violations, suspicious behavior, and API attacks
• Analyzing API traffic without additional network changes or difficult-to-install agents
• Integrating with existing workflows (ticketing, SIEMs, etc.) to alert security/operations teams
• Preventing attacks and misuse in real time with partially or fully automated remediation

API development teams are under pressure to work as quickly as possible. Speed is essential for every application developed, making it easier for a vulnerability or design flaw to happen and subsequently go undetected. Testing APIs in development before they are released into production greatly reduces both risk and the cost of fixing an API that is vulnerable. Core capabilities needed:

• Running a wide range of automated tests that simulate malicious traffic
• Discovering vulnerabilities before APIs enter production, reducing the risk of successful attacks
• Inspecting your API specifications against established governance policies and rules
• Running API-focused security tests that run on demand or as part of a CI/CD pipeline

This comprehensive approach works as a complement to an enterprise’s existing API protection capabilities, which may include:

• The communication channel for API calls and responses needs to be secure. A best practice is to use Transport Layer Security (TLS), which used to be known as Secure Socket Layer (SSL). A TLS certificate uses end-to-end encryption to protect API data and access credentials while they are in transit. TLS protects your information sent via your API through encryption of all messages sent through that API.
• If your URL begins with https rather than http, you will know that your website supports TLS. Without TLS, an attacker can intercept information from the transit server and access it without permission. All authentication methods are undermined by it. TLS requires certificates from certificate authorities that let the user know that your API is legal and protected.

API keys are unique strings that function as API access credentials. They are used for authentication of clients calling on the API.

• API tokens are unique digital identifiers that authenticate API users. Tokens make it possible to avoid burdensome authentication processes like two-step verification and single sign-on (SSO). API admins can grant and revoke API tokens from API users, providing control over API access.
• Tokens are usually issued by the server hosting the API for use by client-side apps. The token mechanism differs from cookie-based session management in that it’s normally stateless. There is no need for the server to store session details — making it easier to scale out infrastructure that uses APIs.

This is a secure standards-based authentication mechanism based on tokens. It works for API user authentication and authorization.

API authentication is a critical barrier to keep malicious actors and threats at bay. A JWT is a digitally signed authentication token that contains data about the API user in JSON. The advantage of a JWT is that it can hold more data than an API key.

• APIs are targets of distributed denial-of-service (DDoS) attacks. An attacker can flood an API with requests and cause it to shut down. To prevent this from occurring, an API security tool can implement rate throttling, e.g., shutting off access if a client tries to invoke the API too often in a given time period.

• It is possible to establish user identities for API clients by integrating API management with identity and access management (IAM) systems. This way, an admin can gain control over who is permitted to use an API, which prevents unauthorized access.

• Hackers may try to trick an API by modifying JSON request data and URL parameters. By validating these parameter-based inputs, it is possible to stop this type of attack before it starts.

This countermeasure establishes a list of permitted HTTP methods for the API, e.g., POST, GET, PUT. By default, this control blocks methods that should not be allowed by a public API user, such as DELETE.

• It is critical to keep track of API usage and performance, ideally in real time. By monitoring APIs, admins can flag anomalous behavior that could indicate an attack in progress. This might include logging failed requests and looking for suspicious patterns.

Given the critical role of API endpoints in REST API architecture, endpoint protection is paramount. Implementing endpoint security solutions ensures that each endpoint is safeguarded against unauthorized access and malicious activities. This includes using API gateways to manage and secure API traffic, enforce policies, and provide a centralized point of access control.

Securing REST APIs is integral to protecting web applications. REST APIs often serve as the backbone of web applications, enabling communication between the client and back-end servers. Implementing security measures, such as application control and access control, helps safeguard both the APIs and the web applications they support.