I Reviewed 50 API Vulnerabilities — They All Shared This One Flaw

Three weeks into 2023, we were already contending with the second major API breach of the year, one that exposed data for 37 million people. If you feel like you’re hearing about API breaches constantly, you’re not alone. In the past year, I’ve personally reviewed 50 real-world API vulnerabilities — from public bug bounty reports to private security audits — and each time I had a front-row seat to yet another “oops” moment in someone’s code. These incidents spanned industries and tech stacks, but by about the tenth one I started getting a strange sense of déjà vu. Different APIs, different bugs, yet a single pattern kept emerging across all of them. By the time I hit vulnerability number 50, the déjà vu was screaming. It turns out all 50 failures boiled down to the same fatal oversight. And it’s an oversight that’s far more common than any of us would like to admit.

APIs Far and Wide — None Safe

One thing that struck me was the variety of APIs involved. We’re talking every flavor you can imagine: classic REST endpoints, shiny new GraphQL queries, internal microservice calls, mobile app backends, even third-party partner APIs. These weren’t “hello world” toy apps either. They lived in cloud-based SaaS products, fintech platforms moving money around, healthcare systems handling personal records, and gritty internal corporate networks. In other words, anywhere you find software, you find APIs — and these vulnerabilities were cropping up everywhere. It didn’t matter if the API was powering a banking app or a pizza delivery service; I saw similar mistakes in places that handled ultra-sensitive data and in places that should have been trivial. It was equal-opportunity insecurity.

In reviewing these cases, I’d sometimes pause and double-check: Is this really a modern GraphQL endpoint in a fintech startup, or am I reading a post-mortem from 2008? The sad truth is that API security best practices aren’t keeping up with API proliferation. One day I’d be looking at a mobile backend API for a healthcare app that leaked appointment details; the next, it was a third-party vendor API in a cloud app that let me invoke admin actions from a regular user account. Big tech, small startup, legacy enterprise — no one was immune. When it comes to APIs, we’ve built a…