What is API security?

A strong API security posture helps ensure that only authorized users and applications access APIs. It functions as a subset of web security but with a specific focus on APIs, which are increasingly vital to enterprise IT management.¹

APIs connect applications, services, systems and databases across the digital world. They enable companies to integrate on-prem and cloud-based databases, connect core legacy systems with modern platforms, and connect deployments in different environments. They also enable organizations to offer services to external developers and partners, and facilitate more connected user experiences.

Developers can, for example, connect new apps and services with customer relationship management (CRM) platforms, enterprise resource planning (ERP) and other systems. These systems are often deployed in different environments, and they rely on APIs for data synchronization.

The proliferation of low-code and no-code tools has also made it easier for both experienced development teams and non-IT personnel to build apps, access APIs and perform API management tasks. But as APIs proliferate, so do the security issues that often accompany them. Nearly all organizations (99%) have experienced API-related security issues in the last year, with more than one-third (34%) of security incidents exposing sensitive or private data.²

Both internal and external APIs and API endpoints can be compromised, but the public nature of external APIs makes them more vulnerable to malicious actors and various types of API attacks. Vigilant API security practices help businesses secure exposed endpoints and protect enterprise data and networks.

APIs are everywhere. The average enterprise-sized business saw roughly 1.5 billion API calls in 2023, a year in which API calls accounted for 71% of total internet traffic.³ And, nearly every application uses at least one API. As such, APIs are foundational elements of modern computer networking, cloud computing and SaaS deployments.

However, their interconnected nature creates unique security challenges that traditional security measures can’t handle. APIs are often used across cloud, on-premises and hybrid setups, and each environment has its own distinct security needs. Security controls that work in one environment might not translate to another, making unified enforcement an ongoing challenge.

APIs also serve as the connective tissue between microservices, each with its own security profile. A single weakness in one API can put an entire system at risk. For example, in the energy sector, API security measures protect data exchanges between meters, monitoring systems and maintenance platforms, helping ensure the integrity of preventive maintenance programs.

Furthermore, most applications use numerous API endpoints, and each endpoint presents a possible entry point for attackers. Endpoints that process sensitive information (medical or financial data, for instance) are particularly lucrative attack vectors. API endpoints significantly expand the attack surface, and without careful monitoring, can leave private data vulnerable to malicious actors.

And because APIs support agile development and CI/CD pipelines, they’re often built and deployed quickly. If security isn’t seamlessly integrated into DevOps workflows, security assessments and testing can lag behind development. Comprehensive API security protocols can minimize and mitigate these issues.

Secure APIs prevent data manipulation during transmission and processing, and they help ensure that only authenticated, authorized users can access key functions and data. In today’s complex computing environments, API security is an indispensable tool for creating trustworthy data interactions, high-availability services and high consumer trust in digital ecosystems.

Unsecured API endpoints can enable malicious actors to gain unauthorized access to sensitive data and disrupt service operations, with potentially calamitous consequences. Common threats include:

• Authentication-based attacks—where hackers try to guess or steal user passwords or use weak authentication mechanisms to gain access to API servers. Today, the majority (95%) of cyberattacks come from authenticated users.²

• Man-in-the-middle attacks—where a bad actor steals or modifies data (login credentials or payment information, for example) by intercepting API requests or responses.

• Code injections and injection attacks—where a hacker transmits a harmful script (to insert false information, delete or reveal data, or disrupt app functionality) through an API request. These scripts display weaknesses in the API interpreters that read and convert data.

• Security misconfiguration—where inadequate default configurations, overly permissive cross-origin resource sharing (CORS) or incorrect HTTP headers expose sensitive user information or system details.

• Denial-of-service (DoS) attack—these attacks send scores of API requests to crash or slow down a server. DoS attacks can often come from multiple attackers simultaneously in what’s called a distributed denial-of-service (DDoS) attack.

• Broken object-level authorization (BOLA) attacks—where cybercriminals manipulate object identifiers at API endpoints to widen the attack surface and gain unauthorized access to user data. BOLA attacks are especially common because implementing proper object-level authorization checks can be difficult and time-consuming.

API security testing verifies that essential security measures (such as user access controls, encryption protocols and authentication mechanisms) are in place to prevent attackers from exploiting APIs. Security tests often involve actively attempting to exploit vulnerabilities in a running application or scanning source code to identify known security flaws. Security teams send assorted requests to API endpoints and check the responses for weaknesses, unexpected behavior and code bugs.

Depending on the type of vulnerability they’re testing for, teams can choose to conduct manual tests, rely on automated testing tools or use a combination of the two.

For example, engineers can use manual penetration testing—or pentesting—to simulate real-world attacks and identify security issues. If a security weakness appears only when an application is running, they might run a Dynamic Application Security Testing (DAST) tool, which can perform security tests on live systems. If they want to scan for flaws or weaknesses in the source code, they can use a Static Application Security Testing (SAST) tool.

Traditionally, the security testing process relied on penetration testing or manual scanning carried out by enterprise security teams. Today, organizations often integrate automated API security tests directly into DevOps pipelines. Regardless of approach, vigilant API security testing enables developers to proactively identify security risks and address them before they expose enterprise data or affect customers.

Both API security and application security are designed to protect data, but they approach data security in different ways.

API security is a subset of application security that prioritizes securing individual endpoints and managing access with fine-grained permissions so that every data exchange is protected. Application security takes a more holistic approach, protecting the entire application stack—from the user interface to data storage and backend systems—to help secure the entire environment.

API security is built for flexibility and speed. It uses real-time monitoring and anomaly detection to quickly identify and respond to threats on every API call. Application security, by comparison, uses a more structural strategy. It employs techniques such as static code analysis and secure coding practices to address vulnerabilities throughout the application.

For authentication, APIs typically use token-based mechanisms such as OAuth and JSON Web Token (JWT), which provide precise, short-lived access to resources. Application security, meanwhile, implements broader controls such as role-based access control (RBAC) to manage user permissions across multiple layers of the system.

App security offers protection against a broad range of threats, and API security provides granular protection against threats that target exposed endpoints. So, teams need both tools to achieve comprehensive data security. Integrating API security measures into a larger application security framework can help businesses create a more secure, resilient software environment and maintain trust with users and partners.

In a dynamic digital economy, APIs are critical to business agility, but their open nature poses significant data security risks. API security breaches have led to massive data leaks, even for large, reputable corporations like John Deere, Experian and Peloton.⁴

And in such a global tech environment, security vulnerabilities can threaten all major service providers, regardless of industry or geographical location. As one example, a 2022 API attack on Australian telecoms company, Optus, exposed the names, phone numbers, passport details and driver’s license information of nearly 10 million customers.⁵  These incidents underscore the importance of API protection.

An increase in API abuse has also accelerated the development of comprehensive API security strategies and tools. Implementing stringent API security protocols protects the data, apps and services that API endpoints make available, while also protecting their availability to legitimate users.

API security isn’t just about protecting endpoints, though. It also prioritizes the security of network interactions such as data transmissions, user requests and inter-app communications across the API lifecycle. Some of the most common API security solutions for safeguarding IT infrastructures include:

Authentication is the process of verifying the identity of a user, system or process. In the context of APIs, it refers to user authentication tokens and protocols—such as OAuth 2.0, API keys and JSON Web Token (JWT specifications)—that make sure that a requester is who they claim to be.

Authorization is the process of verifying what an authenticated user has access to. When a user is authenticated, role-based access controls can limit user access strictly to the resources they need or request.

With encryption, plain text and other types of data are converted from a readable form to an encoded version that can be decoded only by users with a decryption key. Encryption technologies (transport layer security [TLS], SSL connection and TLS encryption protocols, for instance) help security teams ensure that bad actors and unauthorized users can’t intercept or alter API traffic.

Input validation protocols protect APIs against malicious data—such as SQL injection attacks and cross-site scripting—by making sure inputs meet length, type, format and range criteria before they’re processed. Using web application firewalls (WAFs) or XML and JSON schema validation can help security teams automate validation processes, preemptively analyzing incoming requests and blocking malicious traffic before it reaches the server.

Rate limiting secures API resources against brute force and DoS attacks by restricting the number of calls a user or IP address can make within a particular timeframe. Rate limits ensure that all API requests are processed promptly, and that no user can swarm the system with harmful requests.

Like rate limiting, throttling restricts the number of API calls a system receives. However, instead of operating at the user-client level, throttling works at the server-network level. Throttling limits and quotas help secure API backend bandwidth by limiting the number of calls and messages an API can receive per second.

Security headers can be particularly effective for preventing clickjacking attacks, where bad actors disguise malicious hyperlinks under actionable content to trick users into interacting with sites they don’t intend to.

The “content-security-policy” header, for example, tells the browser which resources it can request from the server. The “x-content-type-option” header stops browsers from trying to MIME-sniff content types, and the “strict-transport-security” header enforces secure (HTTPS over HTTP) connections to the server.

API gateways provide a centralized interface for API access, acting as a single point of entry for all of the API requests a system receives. They help organizations manage API access and add an additional layer of network security, especially for open APIs. An API gateway can standardize API interactions and provide features such as caching, analytics, API composition, rate limiting, encryption, logging and access control.

However, an API gateway also presents a single point of failure and introduces additional complexity into the architecture.

Maintaining comprehensive, up-to-date audit logs (and reviewing them often) helps organizations track data access and usage, and maintain records of every API request. Given the complexity of API ecosystems, staying on top of API activity can be labor-intensive. But, auditing and logging procedures can save time when teams need to retrace their steps after a data breach or compliance lapse.

Proactive error handling in API environments can prevent cybercriminals from revealing sensitive information about API processes. Ideally, any API error will return HTTP status codes that broadly indicate the nature of the error, providing sufficient context for teams to address the problem without risking excessive data exposure.

As with any software application or system, vigilant real-time monitoring and maintenance are essential to maintaining API security. It’s important to keep a watchful eye for any unusual network activity and update APIs with the latest security patches, bug fixes and new features.

Organizations should also adopt timely security standards like the Open Web Application Security Project (OWASP)’s API security recommendations. The OWASP API Security Top 10 list, for instance, offers a framework for understanding and mitigating the most critical and common API security threats (such as broken authentication, mass assignment and server-side request forgery).

Every new version of API software comes with security updates and bug fixes that fill in security gaps from earlier versions. But without proper versioning practices, users can accidentally (or intentionally) deploy an outdated version of the API and put sensitive data in harm’s way.

Attentive versioning and documentation practices enable companies to accelerate API development. It helps them phase out older API versions without disrupting services, pushing users toward newer, more secure iterations.

For instance, if a team discovers a security flaw in v1 of an API, they can fix it in v2. And with versioning, security teams can encourage users to migrate from v1 to v2 at their own pace, while making it clear in the version documentation that v1 has a known security vulnerability.

Security testing requires developers to submit standard requests using an API client to assess the quality and correctness of system responses. Conducting regular security tests to identify security gaps helps teams fix API vulnerabilities before attackers have the chance to exploit them.

Zero-trust security practices operate on the principle that no network traffic—whether it comes from inside or outside the organization—should be automatically trusted. Both the user and the device are presumed untrustworthy by default. So, before any traffic can enter or move through the network, user credentials must be thoroughly authenticated.

With a zero-trust approach, businesses can secure their data and APIs so that only authorized individuals gain access, even if an attacker tries to impersonate a legitimate user on a previously approved device.

Securing APIs is critical to IT infrastructure health and data security. API security is poised to remain a key focus area in the coming years, especially as API usage and distribution challenge existing API management solutions.

For instance, the proliferation of open source and no-code APIs is increasing the security risks posed by shadow APIs, which operate outside official oversight. To combat this issue, security teams are adopting more thorough API inventory, documentation, governance and multifactor authentication practices to protect data against emerging API threats.

Security-minded enterprises are also investing in:

Fortifying API gateways has become a growing priority for software developers.⁶ Unlike API endpoints, which are specific interaction points within an API, API gateways are centralized access points for all API requests. They provide protocol translation services for various API protocols, languages and styles—including GraphQL, REST APIs and SOAP APIs—and route calls to backend services.

Modern API gateways offer dynamic rate limiting and threat detection features, creating an additional layer of API security for today’s cloud-native app deployments and microservice-driven IT environments.

Businesses aiming to keep pace with digital innovation will also need to adopt an API security approach that incorporates technologies such as artificial intelligence (AI) and machine learning (ML). AI- and ML-driven security features can already proactively identify threats by picking up anomalous data patterns in API calls. Such tools can also adapt threat detection and response protocols as threats evolve.

As one example, AI-enhanced security measures can implement adaptive authentication, where security tools automatically adjust data scrutiny based on context and behavioral biometrics.

Enterprises are increasingly adopting zero-trust architectures, which prioritize robust authorization and authentication practices for any device or user attempting to interact with APIs. Zero-trust API security principles are especially useful for protecting vulnerable, public-facing APIs and endpoints.⁷

Agentic AI takes the autonomous capabilities of AI technology to the next level. It uses large language models (LLMs), natural language processing (NLP), and ML to perform autonomous tasks on behalf of human users and another systems. However, AI agents rely on APIs to access data, so API security and agentic AI security are inextricably linked.

As developers continue to embrace agentic AI innovation, they will have to contend with the security risks AI agents create. In response, many businesses are empowering AI agents with advanced monitoring, analysis and blocking features to protect both the agents and the APIs they interact with from cyberattacks.

Strategic partnerships with vendors and API security experts will also be vital for achieving comprehensive API protection into the future. Strategic collaborations can help businesses cover every stage of the API security process, from API discovery and threat detection to runtime analysis and incident response.

Data sharing partnerships prioritize the exchange of security data between platforms (sharing vulnerability details and threat intelligence, for instance). This exchange helps consolidate information so that businesses get a clear, unified view of their API security posture. And alliance partnerships enable individual security entities to merge unique strengths and complementary technologies to streamline security management and encourage collaborative development. These strategic partnerships can help businesses benefit from shared security expertise and deliver more resilient digital services to users.

As APIs continue to unlock new networking opportunities, the risks associated with them will evolve in kind (and perhaps even faster). Taking a proactive approach to enterprise API security can help businesses protect sensitive data and develop agile security strategies that fortify their security posture as the threat landscape changes.