The 5 Biggest API Security Threats You Must Know in 2025

Introduction

As APIs become the core interface for businesses, they are increasingly the primary attack vector. The OWASP API Security Top 10 lists the most critical risks. Here are the 5 threats that continue to cause the biggest breaches in 2025.

1. Broken Object Level Authorization (BOLA)

This is the most common and devastating vulnerability. It occurs when a user can access a resource they shouldn't by simply changing the ID in the API call. For example, changing /api/v1/users/123 to /api/v1/users/456 and successfully accessing another user's private data. This is a failure to properly validate the user's **authorization** for the specific resource requested.

2. Broken User Authentication

A weakness in the identity management mechanisms. This includes weak password policies, poor implementation of JWTs, allowing brute-force attacks against login endpoints, or not expiring session tokens properly. The goal of the attacker is to compromise user accounts through credential stuffing or brute force.

3. Excessive Data Exposure

APIs often return more data than the client actually needs. For example, an API might return a full user object including private fields like internal_id or social_security_number, relying on the client-side code to filter it. An attacker intercepting this response gets everything. The solution is **server-side data filtering** to only return necessary fields.

4. Lack of Resources & Rate Limiting (B04)

When there are no limitations on the rate or size of requests, attackers can exploit APIs to drain computational resources, overwhelm databases, or exhaust available memory, leading to a Denial of Service (DoS). This is often an architectural failure, as rate limiting should be enforced at the **API Gateway** layer.

5. Broken Function Level Authorization (BFLA)

Similar to BOLA, but applied to functions or roles. This happens when a standard user can access an administrative endpoint, such as /api/v1/admin/delete_user, simply because the API logic didn't verify their **role** or **privilege level**. Authorization must be checked for every single function called.

Conclusion: Prevention is Foundational

The majority of these threats are preventable with a strong API Gateway security posture and a "deny by default" approach. Always assume the client is malicious and validate every piece of data, every authorization, and every rate limit on the server side.