Most customers never see an API. Yet they use one every time they log in, make a payment, check an order, open a mobile app, or connect a business service. APIs sit quietly behind these interactions, moving data between applications and systems. That makes them useful—and attractive to attackers.
As companies add cloud platforms, mobile applications, microservices, AI tools, and third-party integrations, the number of APIs keeps growing. Each one can become another point that needs to be secured. For technology leaders, API security is no longer just a developer concern. It is part of managing business risk.
What Exactly Is an API?
An API, or Application Programming Interface, allows different software systems to communicate with each other. Think of it as a controlled doorway.
A mobile banking app, for example, might use an API to request an account balance from a backend system. The API receives the request, checks permissions, retrieves the required information, and sends a response. The problem starts when that doorway is not properly protected. An attacker may try to access information they should not see, perform actions they are not authorized to perform, or overwhelm the system with requests.
Where API Security Problems Begin
API vulnerabilities are often less obvious than a traditional login attack. According to the OWASP API Security Top 10, authorization failures, authentication weaknesses, excessive data exposure, and unrestricted resource consumption are among the risks organizations need to consider when securing APIs. (OWASP API Security Project)
Broken Authorization
A user may successfully log in but still shouldn’t have access to everything. Imagine a customer viewing their invoice through an API. If changing an identifier in the request allows them to view another customer’s invoice, the authentication worked—but the authorization failed.
This type of problem is commonly known as Broken Object Level Authorization (BOLA). The system knows who the user is. It simply fails to check what that user is allowed to access.
Weak Authentication
APIs often depend on passwords, tokens, API keys, or other credentials. If these mechanisms are poorly implemented, attackers may steal or manipulate credentials and access systems as legitimate users. Authentication should therefore be treated as more than a login screen. It needs to cover how credentials are issued, stored, validated, expired, and revoked.
Too Much Data
Sometimes an API returns more information than the application actually needs. A customer-facing application might require a name and order status, but the API could accidentally return internal identifiers, account details, or other sensitive fields. The safer approach is simple: Return only what the application actually needs.
Too Many Requests
APIs consume computing resources with every request. An attacker can exploit that by sending a large number of requests or repeatedly triggering expensive operations. This can slow down an application, increase infrastructure costs, or even cause an outage. Rate limits, request controls, and monitoring can help reduce this risk.
The API Inventory Problem
Security teams cannot protect APIs they don’t know exist. Modern organizations may have APIs for:
- Web applications
- Mobile applications
- Internal services
- Payment systems
- Cloud platforms
- AI services
- Business partners
- Legacy applications
The problem is that APIs don’t always disappear when a product changes.
An older API version may remain online long after developers stop using it. A forgotten test endpoint may still be accessible. A third-party integration may introduce another API that security teams don’t regularly monitor.
OWASP identifies Improper Inventory Management as one of its API security risks. Keeping track of API versions, endpoints, hosts, and deprecated interfaces is therefore an important part of security. (OWASP API Security Project)
Why API Security Is a Business Problem
A vulnerable API doesn’t stay inside the development team. It can affect customers, revenue, operations, and reputation. Consider an API connected to a payment system. If an attacker can manipulate an authorization check, the result could involve unauthorized transactions. Or consider a healthcare, financial, or customer-management application. An API exposing sensitive records can create privacy and compliance concerns.
The technical vulnerability may be small. The business consequences may not be. That is why CTOs, CIOs, security teams, and operations managers need visibility into the APIs supporting their business.
How Businesses Can Strengthen API Security
There is no single tool that solves API security. It requires several practices working together.
Know what you have- Maintain an inventory of APIs, including old versions and third-party integrations.
Check authorization on every sensitive action- Don’t assume that an authenticated user is automatically authorized to access every resource.
Minimize returned data- Only expose the information required for the specific operation.
Control request volume- Use rate limiting and other controls to prevent excessive or abusive traffic.
Test before and after deployment- Security testing should cover authentication, authorization, input validation, business logic, and API configuration.
Monitor API activity- Unexpected traffic patterns, repeated failed requests, unusual access patterns, and sudden spikes can provide early warning signs.
Security Has to Follow the API
API security is not something that can be added once and forgotten. It change as businesses change.
A new mobile feature introduces new endpoints. A third-party integration adds another connection. An old application gets replaced but its API remains active. A development team changes how data is returned. Every change can introduce a new security question.
The most useful questions are simple:
Who is making this request?
What are they allowed to access?
What are they allowed to do?
How much data should we return?
What happens if they make thousands of requests?
If an organization can answer those questions consistently, it has a much stronger foundation for managing API risk.
Key Takeaways
- APIs are now part of the infrastructure behind many critical business services.
- Authentication alone does not determine whether a user should access a resource.
- Broken authorization can expose data belonging to other users.
- APIs should return only the information an application actually needs.
- Rate limiting can help protect systems from excessive requests.
- Organizations need an accurate inventory of active, deprecated, and third-party APIs.
- API security should be treated as an ongoing business risk-management process, not a one-time development task.
