API Security Testing for UK Businesses: What It Is and Why It Matters

API security testing for UK businesses: what it is and why it matters

APIs — Application Programming Interfaces — are the invisible infrastructure of the modern web. When your website loads your account details, processes a payment, retrieves your order history, or sends a notification, it is almost certainly making API calls to do so. Most modern web applications are built around APIs, and mobile apps are almost entirely API-driven.

This makes API security one of the most important and most neglected areas of web application security. The vulnerabilities that cause the largest data breaches are increasingly API vulnerabilities rather than traditional web application issues.

Why APIs are particularly vulnerable

APIs are often developed and deployed faster than traditional web interfaces. Development teams under pressure to ship features quickly may skip security reviews, leave debug endpoints accessible, or implement authentication inconsistently across different API endpoints.

APIs also tend to expose more data than web interfaces. A web interface shows you what you are supposed to see. An API endpoint often returns the full data object, including fields that the interface does not display — and those hidden fields may include sensitive information about other users.

The OWASP API Security Top 10 — the authoritative list of the most critical API vulnerabilities — includes broken object level authorisation, where an attacker can access another user's data by changing an ID in the request; broken authentication, where API tokens are poorly implemented or validated; excessive data exposure, where APIs return more data than the application needs; and lack of rate limiting, which enables brute force and enumeration attacks.

Broken object level authorisation — the most common API vulnerability

BOLA — also called IDOR in the context of APIs — is the most frequently exploited API vulnerability. It works like this: your API endpoint is /api/orders/12345, and it returns the details of order 12345. If the API does not verify that the requesting user is actually the owner of order 12345, an attacker can change the number to 12346, 12347, and so on, accessing every other customer's orders.

This vulnerability is endemic in APIs because it requires a specific authorisation check on every single endpoint for every single request. Developers who implement authentication — verifying who you are — but not authorisation — verifying what you are allowed to access — create APIs that are authenticated but not secured.

API authentication weaknesses

API authentication commonly uses tokens — strings of characters that identify and authorise the caller. Weak token generation, tokens that never expire, tokens transmitted over unencrypted connections, and tokens stored insecurely in client applications are all common findings in API security assessments.

JWT vulnerabilities — where the tokens used for API authentication can be forged or manipulated — are particularly prevalent in modern APIs.

What API security testing covers

A thorough API security assessment maps all the endpoints your application exposes, tests each one for authorisation weaknesses, checks authentication implementation, looks for excessive data exposure, tests rate limiting, and probes for injection vulnerabilities in API parameters.

Yrzo AI includes API security testing as part of its 44 automated checks, probing your application's API endpoints for the most common and impactful vulnerabilities. Starting at £399 with a full report in under 20 minutes.