API Security: The Underestimated Attack Surface of Modern Enterprises

APIs are the backbone of modern software architectures — and at the same time, the fastest-growing attack vector. By 2024, 40 percent of all web attacks will occur via APIs. Most companies do not protect their APIs nearly as rigorously as their web applications.

TL;DR

Attack Surface: APIs account for 83% of all web traffic — and are attacked three times more frequently than classic web applications.
Main Risk: Broken Object Level Authorization (BOLA) is the most common API vulnerability and allows unauthorized access to other users’ data.
Dark Figure: The average company has 30% more APIs exposed than documented — Shadow APIs represent a massive security risk.
Protection: API Gateway + Runtime Protection + Shift-Left-Testing form the three lines of defense.
Standard: The OWASP API Security Top 10 (2023) is the definitive reference framework for securing APIs.

Why APIs Are the New Entry Point

Every modern application communicates via APIs – with other applications, cloud services, partners, and mobile apps. Akamai reports that APIs make up 83 percent of all web traffic. Yet they’re often far less protected than the applications they serve.

Why? Web applications have benefited from two decades of hard-won defenses: WAFs, Content Security Policies, and browser-level security features. APIs rarely enjoy comparable protection. They’re direct conduits to business logic and databases – making them attackers’ most attractive target.

High-profile breaches underscore the danger: In 2022, Optus (Australia’s second-largest telecom) exposed data from 10 million customers through an unprotected API. In 2023, T-Mobile US was compromised via an API vulnerability – affecting 37 million customer records.

OWASP API Security Top 10

The OWASP API Security Top 10 (updated in 2023) defines the most critical risks:

1. Broken Object Level Authorization (BOLA): The API fails to verify whether the calling user is authorized to access the requested object. An attacker simply modifies an ID in the request and gains access to another user’s data. It’s the most prevalent vulnerability – and trivial to exploit.

2. Broken Authentication: Weak or missing authentication mechanisms – such as unrotated API keys, absent rate limiting, or unchecked tokens.

3. Broken Object Property Level Authorization: The API returns more data fields than the user should see. Mass Assignment lets users modify fields they shouldn’t control.

4. Unrestricted Resource Consumption: No limits on API calls, data volume, or compute resources – enabling DoS attacks and runaway cloud costs.

Three Lines of Defense

Line 1: API Gateway. A centralized entry point for all API traffic. Handles authentication, rate limiting, request validation, and TLS termination. Tools include Kong, Apigee, AWS API Gateway, and Azure API Management.

Line 2: Runtime Protection. Real-time monitoring of API traffic to detect anomalies, BOLA attempts, and unusual data access patterns. Specialized tools like Salt Security, Noname Security, or 42Crunch analyze behavioral signals – catching attacks that rule-based systems miss.

Line 3: Shift-Left-Testing. Embed API security testing directly into the development pipeline: OpenAPI spec validation, SAST for API code, and automated DAST scans against staging environments. Finding flaws early slashes remediation costs.

Shadow APIs: The Invisible Risk

Salt Security reports that the average enterprise exposes 30 percent more APIs than it documents. These Shadow APIs emerge from forgotten test environments, deprecated endpoints left running, and internal APIs accidentally exposed to the public internet.

They’re especially dangerous because they operate outside governance: no authentication, no monitoring, no patching. So the first step in any API security initiative must be a comprehensive, automated API inventory – built from live traffic analysis, not developer surveys.

Key Facts at a Glance

API Attack Share: 40% of all web attacks (Akamai, 2024)

API Traffic Share: 83% of all web traffic (Akamai)

Most Common Vulnerability: BOLA – found in 68% of all API penetration tests (Salt Security)

Shadow APIs: 30% more exposed APIs than documented (average)

Source: OWASP, Akamai, Salt Security, Gartner, 2023/24

Frequently Asked Questions

What is the difference between API security and web security?

Web security protects the user interface; API security protects the programmatic interfaces behind it. APIs expose business logic and data more directly than web applications – requiring specialized safeguards like BOLA detection and strict schema validation.

Is an API Gateway sufficient for API security?

No. While gateways provide foundational controls – authentication, rate limiting, basic request filtering – they can’t defend against business-logic attacks like BOLA or mass assignment. That requires dedicated runtime protection.

How do I find Shadow APIs?

Through network perimeter traffic analysis. Tools like Salt Security or Noname Security automatically discover APIs by inspecting HTTP traffic. Supplement with cloud log analysis and periodic external scanning.

How much does API security cost?

API Gateway: starting at €500/month. Runtime Protection: €2,000-€10,000/month, scaled to API volume. Shift-Left tools: often open source or from €200/month. The return on investment becomes clear with the first prevented data breach.

Are GraphQL APIs more secure than REST?

Not inherently. GraphQL introduces its own risks – introspection leaks, query depth attacks, and batching abuse. Core security principles remain identical; only implementation details differ.