Critical API Security Failures That Could Break Your Business (And How to Prevent Them)

APIs have become the connective tissue of modern software ecosystems, driving integrations, enabling automation, and powering digital experiences behind the scenes. But as their role expands, so does their appeal to attackers.

Poorly secured APIs don’t just expose data — they expose businesses to operational, reputational, and regulatory risk. In this post, we’ll break down the most common security pitfalls seen in real-world projects and share actionable strategies to close those gaps — before they become costly incidents.

What Are the Main Security Gaps in APIs?

The list of security gaps and ways to expose an API can be extensive. Below, I’ll focus on the most common things I’ve found during my time working as an IT professional in the projects I’ve participated in. I’ll review these areas and how they map to OWASP’s 2023 top ten list for API risks.

Weak Authentication Mechanisms

Examples of this kind of failure include leaving simple API keys in plain text without encryption or the absence of any authentication method, leaving the API completely unprotected and “public,” allowing anyone to make requests and enabling unauthorized access.

The latter is also the second-ranked vulnerability in OWASP’s list (to be more exact, API2:2023 Broken Authentication). Attackers easily detect this gap, and the business impact is severe for those who suffer this kind of vulnerability.

Insufficient Authorization Controls

Authentication and authorization are two different things. Even if an authentication mechanism is implemented to access the API, is the caller actually authorized to make that request?

For example, a system or user authenticates using a valid token assigned to a system or personal user, but how do we know they’re truly allowed to access this API? What about specific underlying resources?

Unauthorized access is a severe vulnerability since it can expose sensitive data, critical functionalities that not everyone should have access to, and statistics that should remain private.

About severity, realize that this can be related to two Security Risks from OWASP 10 (API5:2023 Broken Function Level Authorization and API1:2023 Broken Object Level Authorization), both the first and the second most common vulnerability explored by an attacker.

Also read: What Is Broken Object Level Authorization? (And How To Fix It) Injection Attacks

Just like in web applications, APIs are also susceptible to injection attacks (SQL injection, command injection, cross-site scripting (XSS)). Payloads or parameters (path and query parameters) received by APIs can contain malicious code or calls that lead to dangerous and failure-prone situations.

This is one of the easiest vulnerabilities to exploit and fits really close to the risk called API10:2023 Unsafe Consumption of APIs from OWASP 10. The successful exploitation may lead to sensitive information exposure to unauthorized actors, many kinds of injections, or denial of service.

Insecure Data Transmission

APIs that transmit sensitive data over insecure channels without encryption (lacking HTTPS or Mutual SSL) are at risk of interception and data spying, commonly known as sniffing. In this scenario, returned data or even authentication information becomes vulnerable.

From the perspective of risk, guided by the OWASP 10 list, this vulnerability can be addressed as API3:2023 Broken Object Property Level Authorization and leads to another risk called PI3:2019 Excessive Data Exposure.

This strongly points to the need for proper cryptographic controls during data transmission, which is a key aspect of preventing sensitive data exposure.

Incorrect CORS Configuration

Cross-origin resource sharing (CORS) is a security mechanism implemented by web browsers that controls how web pages from one domain (origin) can request resources from a server at a different domain (origin). It’s designed to prevent malicious websites from making unauthorized requests to your APIs on behalf of a user.

Misconfigured CORS settings can allow unauthorized requests from untrusted origins, potentially exposing sensitive data or enabling attackers to perform unauthorized actions. This is linked to the API8:2023 Security Misconfiguration risk from the OWASP 10 list.

For example, a misconfigured CORS policy might fail to specify which frontends or devices are allowed to access your API or which HTTP methods they’re permitted to use.

Lack of Rate Limiting and Flow Control

APIs that do not implement rate limiting or throttling controls are vulnerable to abuse, such as excessive resource consumption (either from the API itself or backend systems) and a flood of requests that may reveal architectural weaknesses.

Although this is not directly listed on the last version of OWASP 10, during the 2019 ranking, there was a specific category for this kind of vulnerability (API4:2019 Lack of Resources & Rate Limiting).

Related: Different Algorithms to Implement Rate Limiting in APIs Denial-of-Service (DoS) Attacks

Closely related to rate limiting, APIs can be targeted by DoS attacks that disrupt service availability by overwhelming the system with a high volume of requests.

Exploitation requires simple multiple concurrent API requests and can be performed from a single local computer or by using cloud computing resources. Most of the automated tools available are designed to cause DoS via high loads of traffic, impacting an API’s service rate.

This is the fourth most common vulnerability according to the OWASP top ten list (aka API4:2023 Unrestricted Resource Consumption).

Inadequate Logging and Monitoring

Without well-configured logs (in terms of both content and level) and proper monitoring tools, it becomes difficult to detect and respond to security incidents or unusual activity. Observability is essential for APIs today.

In the OWASP 10 rank from 2019, this vulnerability had an exclusive topic (API10:2019 Insufficient Logging & Monitoring), and apart from not being on the last list, it’s still dangerous and easy to explore.

Incorrect Security Configurations

Improper configurations in API servers, frameworks, or platforms can introduce security vulnerabilities such as default passwords, unnecessary features enabled, or improper access controls. In other words, API gateways, load balancers, or development frameworks can all impact API security if left misconfigured or in their default “factory settings.”

Security misconfigurations can happen at any level of the API stack, from the network level to the application level. This can lead to exposing sensitive user data and system details but also full server compromise.

Data Exposure

APIs can unintentionally expose sensitive information—such as credentials, personally identifiable information (PII), or proprietary data—through verbose responses or error messages.

This is one of the most dangerous vulnerabilities, not only from the technical side but also from business impacts for companies, which can suffer reputational damage, loss of customer trust and loyalty, negative publicity, devaluation of intellectual property, stock price decline, and many others.

Best Practices to Address Security Gaps

Now, I’ll share some simple actions that, at the end of the day, can increase your level of security and avoid headaches for your project and your company. Many of these are obvious actions, but sometimes the obvious is not always on top of your mind during a rushed development process.

Implement Strong Authentication & Authorization

Implement robust authentication mechanisms such as OAuth 2.0, JWT (JSON Web Tokens), or API keys (with proper encryption methods) to verify the identity of clients accessing the API. The basic client_id plus client_secret flow to obtain an access_token already helps resolve many authentication issues.

Also, adjust permissions to define who can access the API and how. Remember that authorization can be configured at both the API level and the resource level. That is, depending on the API, you might enforce general access control and more specific permissions, for example, requiring special authorization for a POST method.

Another recommendation is to implement role-based access control (RBAC) or attribute-based access control (ABAC) as needed.

Use Encryption

Use HTTPS/TLS or Mutual TLS to encrypt data transmitted between clients and the API server, protecting against eavesdropping and tampering. This is one of the simplest and most essential controls to implement.

Validate and Sanitize Input

Create input validation rules for payloads and parameters. Nowadays, many API managers offer built-in payload validation features. However, if such tools are unavailable, you can develop your own validation mechanisms — similar to what is commonly done for [web forms](https://nordicapis.com/form-building-made-easy-10-apis-to-simplify-the-process/ — to help prevent injection-style attacks.

Use Rate Limiting and Flow Control

Implement rate limiting and flow control mechanisms to reduce the risk of abuse, denial-of-service (DoS) attacks, and excessive resource consumption. Also, keep in mind to always review it per API or per HTTP method from time to time, as our business rules change.

Configure CORS Correctly

Properly configure CORS headers to restrict cross-origin requests and prevent unauthorized access. Identify who is calling the API and from where, filtering requests and limiting access accordingly. Tracking this is fundamental to knowing where the request is coming from.

Adopt Security Headers

Use security headers such as Content Security Policy (CSP), X-Content-Type-Options, X-Frame-Options, and X-XSS-Protection to enhance security and mitigate various types of attacks.

Follow The Rule of Least Privilege

Expose only the necessary data through the API. Carefully refine what the API really needs to provide or receive in payloads to reduce the risk of data exposure and limit the impact of security breaches.

Regularly Log and Monitor

Ensure logs are well-structured and appropriately leveled. When deciding what to log, consider the kind of request information to include and what you really need to identify for troubleshooting. Logging and observability tools can help you discover vulnerabilities and understand your API’s health.

Metrics such as request volume, error count, most common errors (by status code), and average response time provide a baseline understanding of API behavior. Based on these metrics, you can take action. For example, an excess of 500 errors or a spike in 403 errors may indicate unauthorized access attempts or someone trying to bypass your API’s authentication.

Perform Security Testing

Conduct regular security assessments, penetration testing, and vulnerability scanning, a black-box test used to discover vulnerabilities from an external perspective.

Secure The Entire SDLC

Integrate security into every stage of the software development lifecycle (SDLC)—from design and development to testing and deployment—ensuring that security is prioritized throughout the entire process.

Some other tips include versioning to manage changes to the API and maintain backward compatibility, allowing clients to gradually upgrade to newer versions with improved security. Another is educating developers, administrators, and users on security best practices, secure coding principles, and common threats to foster a culture of security awareness.

APIs Are Your Brand: Secure Them Accordingly

In today’s digital economy, APIs are the backbone of innovation, integration, and customer experience. But with great connectivity comes great responsibility. When API security is treated as an afterthought, organizations don’t just risk technical failures — they jeopardize their entire business. Data breaches, service disruptions, and unauthorized access can translate into regulatory fines, operational downtime, and, most damaging of all, a loss of customer trust.

The reputational impact of a security incident can be swift and unforgiving. News travels fast, and a single vulnerability left unaddressed can dominate headlines, erode brand credibility, and shake investor and consumer confidence. No product launch or development timeline is worth the cost of a public security failure.

Strong API security is not just about code — it’s about culture. Building secure APIs means embedding security into every phase of the software lifecycle, aligning teams around shared accountability, and treating security as a business enabler rather than a blocker. Organizations that make API security a strategic priority position themselves to innovate with confidence, meet compliance demands, and earn long-term trust.

In the end, your APIs reflect your business. Make sure they reflect a company that takes security — and its reputation — seriously.